Category Archives: Physics Primer

In chemistry, every element is represented by a one- or two-letter symbol¹. The first letter is always capitalized, the second is in small case. You can find the symbols listed in a periodic table, a chart which lists the chemical elements in order of atomic number in such a way that related elements appear in the same columns (that statement is oversimplified, but it will have to do for now)². There are many periodic tables available on the Web, but the one I suggest you take a look at first is Michael Dayah’s Dynamic Periodic Table, which you can view by clicking here. Note that you can amplify the information on any element by moving your cursor over it.

As you can see, most symbols are abbreviations of the element’s name: H for hydrogen, O for oxygen, Cl for Chlorine, and so forth. But quite a few symbols are not that way: Fe for iron, Ag for silver, Au for gold, for example. When I was younger, I wondered why that was. Why not use Ir for iron, Sv for silver, and Gl for gold? Then it dawned on me — not every chemist is an American who speaks English. Most of the elements that have funny symbols have been known to mankind for a very long time, and different languages have different words for these elements. “Iron” is fer in French, hierro in Spanish, Eisen in German, zhyelyezo in Russian, and barzel in Hebrew. Which language should we use for the symbol? It made sense to choose a classical language that is universally recognized but no longer spoken, and in Latin the word for “iron” is ferrum. That is why the chemical symbol for iron is Fe³.

Here are the more common symbols you are likely to encounter in chemical formulas, at least in this blog, ordered by atomic number.⁴:

Note: Average atomic mass refers to the average mass of all atoms of that element found in nature, measured in daltons. It is numerically equal to the molar mass of the element as measured in grams per mole.

Using the element symbols, we can then represent chemicals with a shorthand notation called a chemical formula⁷. Each element that makes up the chemical is represented by its symbol in the periodic table. If two or more atoms of the same element make up the chemical, the number of atoms appears as a subscript following the symbol.

Let’s start by showing how molecules are represented by formulas. The formula shows how many atoms of each element make up the molecule. Hydrogen molecules consist of two hydrogen (H) atoms each, so the chemical formula for hydrogen gas is⁸:

H₂

Water molecules consist of two hydrogen atoms attached to an oxygen (O) atom, so its formula is the familiar⁹:

H₂O

A common form of gasoline is octane, whose molecule consists of a chain of eight carbon (C) atoms surrounded by 16 hydrogen atoms. Its formula is¹⁰:

C₈H₁₆

Chemical formulas can also represent ionic compounds. Here the formula doesn’t describe a molecule, but rather the proportion that each element appears in the compound. By convention, cations always appear before anions. In a previous post, we encountered a chemical called calcium chloride, which consists of two chlorine (Cl) anions for every calcium (Ca) cation. Its chemical formula is¹¹:

CaCl₂

In a previous post, we discussed how molecules can form parts of larger compounds, either as polyatomic ions or as functional groups of larger organic (carbon-based) molecules. When we write a formula for a compound having polyatomic ions or functional groups, we want the formula to show these groups. For example, we came across the compound ammonium nitrate, which consists of two nitrogen (N) atoms, three oxygen atoms, and four hydrogen atoms¹². One might think that its formula should be written:

N₂O₃H₄

but that would obscure the fact that ammonium nitrate is made of two polyatomic ions:

• The ammonium cation, which is a molecule consisting of a nitrogen atom with four hydrogen atoms attached. Its chemical formula is NH₄.
• The nitrate anion, which is a molecule consisting of a nitrogen atom with three oxygen atoms attached. Its chemical formula is NO₃

That is why the accepted formula for ammonium nitrate is¹²:

NH₄NO₃

As you can see, the formula for ammonium nitrate simply puts the formulas for the ions together. The ratio between ammonium and nitrate ions is 1:1.

Acetic acid is the main component of vinegar. Its molecule consists of two carbon atoms, four hydrogen atoms, and two oxygen atoms. As such, its formula is commonly given as¹³:

C₂H₄O₂

But this formula obscures an important part of the acetic acid molecule, the carboxyl group COOH. To show the carboxyl group, its formula is frequently written as¹⁴:

CH₃COOH

(You may ask why I did not represent the carboxyl group as CO₂H, although I’ve seen that notation as well. The COOH formula emphasizes that the carbon atom [C] is bonded to an oxygen atom [O] and to a hydroxyl group [OH]¹⁵.)

Just like elements can appear more than once in a chemical formula, so can polyatomic ions and functional groups. When this happens, the group is enclosed in parentheses. Calcium hypochlorite is a compound used in sanitizing swimming pools. It consists of two ions: the calcium cation (an element, symbol Ca) and the hypochlorite anion (a molecule consisting of a chlorine atom attached to an oxygen atom, formula ClO). There are twice as many hypochlorite ions as calcium ions, therefore the formula is¹⁶:

Ca(ClO)₂

Chemical formulas are used in describing chemical reactions, in which a chemical breaks up into simpler chemicals, or two or more chemicals recombine into new chemicals. We can represent chemical reactions with a notation called a chemical equation. On the left side are the formulas for the chemical or chemicals that start the reaction, on the right side are the symbols for the product or products of the reaction. Plus signs (+) connect the compounds on either side of the equation. Separating the two sides in the middle is a right arrow (→) showing the direction of the reaction¹⁷. There must be as many atoms of each element on the right side of the equation as there are on the left side.¹⁸

For example, carbon burns in the presence of oxygen to form the compound carbon dioxide. This is how we represent the reaction with a chemical equation¹⁹:

C + O₂ → CO₂

A chemical equation can be read in two ways. First, it can show how various atoms, ions, molecules, and functional groups combine and separate to form new molecules and ionic compounds. Second, it specifies the proportions that amounts of chemicals react with each other as measured in moles. By knowing the molar mass of each substance, you can then calculate the masses of the reacting substances and their products²⁰. Bear in mind that the molar mass of a homogeneous chemical is equal to the sum of the molar masses of the elements in the proportions that make it up²¹.

There are two ways to read the equation above describing carbon combining with oxygen:

1. One atom of carbon combines with the two atoms in an oxygen molecule to form one carbon dioxide molecule.
2. One mole of carbon (12 grams) combines with one mole of oxygen gas (32 grams) to form one mole of carbon dioxide (44 grams).

Here’s what happens when hydrogen and oxygen gas combine to form water²²:

2H₂ + O₂ → 2H₂O

Again, you can read this equation in two ways:

1. Two molecules of hydrogen gas combine with one molecule of oxygen gas to form two molecules of water. Note that the same numbers of atoms of both elements appear on both sides of the equation: four hydrogen atoms and two oxygen atoms.
2. Two moles of hydrogen gas (4 grams) combine with one mole of oxygen gas (32 grams) to form two moles of water (36 grams).

Chemical equations can also describe ionic reactions. Sodium metal will combine with chlorine gas to form table salt²³:

2Na + Cl₂ → 2NaCl

Two atoms of sodium metal will react with one molecule of chlorine gas to form table salt. Note that the formula 2NaCl does not represent two molecules since table salt is an ionic compound. The "2" is necessary to keep the number of atoms on each side of equation balanced.

But the second way to read the equation is that two moles of sodium (46 grams) combine with one mole of chlorine gas (about 71 grams) to form two moles of table salt (117 grams). Here the need for the "2" is more obvious.

Finally, polyatomic ions and functional groups can be represented in chemical equations. Calcium hypochlorite is made by mixing calcium hydroxide (hydroxide is a polyatomic anion) with chlorine gas²⁴:

2Ca(OH)₂ + 2Cl₂ → Ca(ClO)₂ + CaCl₂ + 2H₂O

Two calcium cations and four hydroxide anions react with two chlorine gas molecules to form the ionic compounds calcium hypochlorite and calcium chloride, plus two molecules of water.

Alternatively, two moles of calcium hydroxide (148 grams) combine with two moles of chlorine gas (142 grams) to form one mole of calcium hypochlorite (143 grams), one mole of calcium chloride (111 grams), and two moles of water (36 grams).

In the next post, we will discuss the nature of energy.

Footnotes

1. Strictly speaking, there are elements with three-letter abbreviations, but they are all newly discovered elements with half-lives too short to be of any practical value.
2. Freudenrich, Craig, How the Periodic Table Works. HowStuffWorks website. To view, click here. See also Western Oregon University website. A Brief History of the Development of the Periodic Table. To view, click here. See also the American Institute of Physics website, Marie Curie and the Science of Radioactivity: The Periodic Table of the Elements. To view, click here. I discovered a very entertaining periodic table on the web. Gray, Theodore and Whitby, Max. Photographic Periodic Table of the Elements. To view, click here.
3. Our modern system of chemical symbols was invented by the Swedish chemist Jöns Jacob Berzelius (1779 – 1848). van der Krogt, Peter, Development of the chemical symbols and the Periodic Table, on Mr. van der Krogt’s personal website. To view, click here.
4. Information taken from Michael Dayah’s Dynamic Periodic Table, which you can view by clicking here.
5. Lead is the only element in this list that I could not find an average atomic mass accurate to two decimal places. All the sources I looked up listed the average atomic mass of lead as 207.2 daltons. I wonder why.
6. This is not the average atomic mass of plutonium but the mass of its longest-lived isotope. This is because plutonium is not found in nature but only manufactured in nuclear reactors, so it can’t have an average mass of all its atoms found in nature.
7. NDT Resource Center website (operated by the Collaboration for Nondestructive Testing Education). Chemical Formula. To view, click here. For a more in-depth explanation of chemical formulas, see the Washington University at St. Louis website, Chemical Formulas. To view, click here.
8. The Chemical formula website. Hydrogen. To view, click here.
9. The Chemical formula website. Water, H₂O. To view, click here.
10. Helmenstine, Anne Marie, About.com Chemistry website. Octane Chemical Structure. To view, click here.
11. This is the formula for anhydrous calcium chloride, calcium chloride that has not absorbed water into its crystal structure. National Institute of Health’s PubChem website. Calcium chloride anhydrous. To view, click here.
12. Helmenstine, Anne Marie, About.com Chemistry website. Ammonium nitrate. To view, click here.
13. National Institute of Health’s PubChem website. Acetic Acid. To view, click here.
14. Helmenstine, Anne Marie, About.com Chemistry website. Vinegar Chemical Formula. To view, click here.
15. Pearson Prentice Hall website.Concept 6 Review: The Carboxyl Group. To view, click here. Also, see the U.S. Department of Energy’s NEWTON: Ask a Scientist! website. Acetic Acid CH3C00H not C2H4O2. To view, click here.
16. Dictionary.com website. Calcium Hypochlorite. To view, click here. Note that their formula slightly varies from ours in that it shows the hypochlorite anion as OCl rather than ClO: Ca(OCL)₂.
17. Helmenstine, Anne Marie, About.com website. What is a Chemical Equation?. To view, click here.
18. Helmenstine, Anne Marie, About.com website. Balancing Chemical Equations. To view, click here. The art of balancing chemical equations is called stoichiometry. See also the Purdue University Bodner Research Web website, Balancing Chemical Equations. To view, click here.
19. University College Cork website. Combustion of Carbon. To view, click here.
20. This follows from the definition of molar mass. The molar mass is the amount of grams in every mole. If you know how many moles of the substance you have, you just multiply by the molar mass to get the mass in grams. Similarly, if you have a known mass in grams of a certain substance and you know its molar mass, divide the mass by the molar mass to get the number of moles.
21. This also follows from the definition of molar mass. One mole of a substance has as much mass in grams as a molecule of the substance has in daltons (for ionic compounds, treat the proportion of ions as reflected in its chemical formula as if it were a molecule. For example, calcium chloride is CaCl₂). But the mass of a molecule is equal to the sum of the masses of atoms that make it up. Therefore, the molar mass of the substance must equal the sum of the molar masses of the elements in the proportions that they appear in the molecule. In our example, the molar mass of calcium chloride is equal to the molar mass of calcium plus twice the molar mass of chlorine.
22. Purdue University Bodner Research Web website. Chemical Equations. To view, click here.
23. Angelo State University website. Sodium + Chlorine: Pass the Salt, Please. To view, click here.
24. Wikipedia. Calcium Hypochlorite To view, click here.

Every atom has a mass measured in daltons (also called unified atomic mass units, abbreviated as amu or just u¹). Protons and neutrons each have about the same mass equal to about one dalton². Therefore, the mass of an atom is the sum of its protons and neutrons, called its mass number³. Most hydrogen nuclei consist of a lone proton, so the atomic mass of most hydrogen atoms is 1 dalton. Most helium nuclei have two protons and two neutrons, so the atomic mass of most helium atoms is 4 daltons. Most iron nuclei have 26 protons and 30 neutrons, so the atomic mass of most iron atoms is 56 daltons.

While the atoms of any one element all have the same number of protons, the number of neutrons can differ. Each possible number of neutrons in a particular element’s nucleus is called an isotope of that element⁴. Hydrogen has three isotopes:

• regular hydrogen with no neutrons (1 dalton)
• deuterium having one neutron (2 daltons)
• tritium with two neutrons (3 daltons)⁴

The isotopes of hydrogen have individual names, hydrogen, deuterium, and tritium. When distinguishing among isotopes of all other elements, it is common practice to write the mass number after the name of the element. Oxygen has three isotopes:

• oxygen 16 with eight neutrons (16 daltons)
• oxygen 17 with nine neutrons (17 daltons)
• oxygen 18 with ten neutrons (18 daltons)⁵

The two most prominent isotopes of uranium are uranium 238 and uranium 235. Uranium 238, with 146 neutrons, is by far the more common isotope. But only uranium 235, with 143 neutrons in its nucleus, can undergo fission and produce nuclear energy⁶.

Periodic tables list the average atomic mass of each element. This is a weighted average of the masses of all the isotopes for that element as they appear in nature. If an element has three isotopes with atomic masses A, B, and C, and isotope A appears p% of the time, isotope B appears q% of the time, and isotope C appears r% of the time (p + q + r = 100%), then the average atomic mass of the element is⁷:

pA/100 + qB/100 + rC/100

For example, chlorine has two isotopes: 76% of all chlorine atoms and ions in nature are chlorine 35, but 24% are chlorine 37. The average atomic mass of chlorine is:

(.76)(35 daltons) + (.24)(37 daltons)

which gives an average atomic weight of 35.48 daltons for chlorine. (Actually, the real average atomic weight is 35.45 daltons, the difference being due to imprecision in the atomic mass values that I used.

As atoms have their masses, so do molecules. The mass of a molecule is the sum of the masses of the atoms that make it up⁸.

The most common type of water molecule has a mass of 18 daltons: its lone oxygen atom is 16 amu, and the two hydrogen atoms contribute 1 dalton each.

The most common carbon dioxide molecule has a mass of 44 daltons the carbon atom has a mass of 12 amu, and the two oxygen atoms contribute 16 daltons each. If these molecules have heavier isotopes within them, the mass will vary accordingly.

Ionic compounds like table salt also have molecular mass, although they are made up of ions, not molecules. Here what is important is the ratio of ions to each other and the average atomic weight of the ions in the compound. If two ions appear in a compound, ion A and ion B, then consider the following. Ion A has an average mass of m_A and ion B has the average mass of m_B. For every x number of ion A in the compound, there is a number of y ions in the compound (i.e. the ratio of ion A to ion B is x:y). The molecular mass of the compound is then:

xm_A + ym_B

expressed in daltons⁹.

For example, the chemical calcium chloride. This chemical consists of calcium and chlorine ions at a ratio of 1:2 (there are twice as many chlorine ions as calcium ions). If the chemical was taken from nature (as opposed to being produced in the laboratory from unusual isotopes), then the average calcium nucleus has a mass of 40.078 daltons and the average chlorine nucleus has a mass of 35.453 daltons. The molecular mass of calcium chloride is the average weight of a calcium ion added to twice the average weight of a chlorine ion:

40.078 + (2 × 35.453)

which is equal to 110.984 daltons, the molecular mass of calcium chloride.

A very important quantity in chemistry is the mole. We define the mole of a homogeneous substance, a substance consisting solely of one element or one chemical compound, such as pure oxygen or pure water. A mole of such a substance has as much mass in grams as the substance’s average molecular mass measured in daltons¹⁰. One mole of hydrogen has the mass of about one gram. A mole of helium has the mass of about four grams. A mole of water has a mass about 18 grams, and a mole of calcium chloride has a mass of 110.984 grams. The number of grams per mole of a particular substance is called the molar mass of that substance. If the substance is homogeneous, its molar mass in grams per mole will be numerically equal to the average molecular mass of the individual molecules expressed in daltons.

Footnotes

1. Princeton University website. Unified atomic mass unit. To view, click here. Note that the article states that the abbreviation “amu” for atomic mass unit has been deprecated in favor of the abbreviation “u” or the unit Dalton (abbreviation: Da).
2. Texas A & M University, Chemistry website, First Year Chemistry Program, Educator Resources, [Isotopes] Introduction. To view, click here. As you can see on the website, protons and neutrons have nearly but not exactly the same mass. Neutrons have slightly more mass than protons. But the differences are very slight, so for many purposes one dalton is a very good approximation for the mass of both the proton and the neutron, although it is insufficient for exact calculations. Technically, one dalton is defined as exactly ¹/₁₂ of the mass of a carbon-12 nucleus, one that has six protons and six neutrons (see reference in previous footnote). Also note that the mass of the nucleus can be less than the sum of masses of its protons and neutrons — the difference called the mass defect (that is why the mass of a carbon-12 nucleus is exactly 12 daltons but the sum of the masses of six protons and six neutrons is 12.09565 daltons). To learn more, see the Purdue University Department of Chemistry website, Nuclear Binding Energy. For a list of precise masses of various isotopes and the proportion they occur in nature, see the Scientific Instruments Services website, Exact Masses of the Elements and Isotopic Abundance.
3. ChemistryUnderstood.com website. How to Find Mass Number. To view, click here.
4. University of Colorado at Boulder website, Physics 2000. Isotopes. To view, click here
5. Thomas Jefferson National Accelerator Facility website. Isotopes of the Element Oxygen. To view, click here.
6. World Nuclear Association website. What is Uranium? How Does it Work? To view, click here.
7. Helmenstine, Anne Marie, Atomic Weight Calculation: Calculating Atomic Weight of an Element with Isotopes. About.com Chemistry website. To view, click here.
8. Miriam Webster online dictionary. Molecular Mass. To view, click here.
9. I didn’t find this formula anywhere, I derived it on my own. But I tried it the Biological Magnetic Resonance Data Bank Molecular Mass Calculator, and it works. Actually, there is a mental short cut you can use. If you know the chemical formula of the ionic compound (we discuss chemical formulas in the next post), you can treat the formula as if it described a molecule. The chemical formula for calcium chloride is CaCl₂. If this was a molecule, it would have a mass anywhere from 110 to 122 daltons. Based on the natural frequency of isotopes, the average calcium chloride “molecule” would have a mass of 110.984 daltons. But there is no such molecule, only ions. We take this as the molecular mass of calcium chloride nonetheless.
10. Frostburg State University General Chemistry Online website. Moles confuse me — why are they used? To view, click here. Note that the web page first defines the mole in terms of Avogadro’s number: 6.02 × 10²³ molecules. But I was taught to think of a mole as a measure of mass with as many grams as one of its molecules has in daltons, and I find it easier to deal with in this way.

How do atoms, ions, and molecules behave in the three familiar states of matter — solids, liquids, and gases?

In solids, ions and molecules are fixed in place, so that the distance between each molecule and its neighbors does not change much. The molecules are vibrating, however.

In liquids, the molecules are free to move, but they stay in contact with one another, slipping and sliding over each other. This is like a bowl full of round marbles that is constantly being agitated.

in gases, the molecules fly around freely, limited only by gravity and the shape of the container around them¹.

Footnotes

1. Purdue University Department of Chemistry website. States of Matter. To view, click here.

There are currently 114 recognized types of atoms, called elements, the type depending on the number of protons in the nucleus¹. The first element, hydrogen, has only one proton in its nucleus. Hydrogen has two, lithium has three, and so on (the number of protons is called the atomic number of the element)¹. Of these 114 elements, 91 elements make up almost all substances in the universe in various combinations². Many familiar substances are made of just one element, substances like graphite and diamond (carbon), nitrogen gas, oxygen gas, neon, aluminum, iron, copper, silver, gold, mercury, lead, and uranium. But most substances are chemically composed of more than one element, and these substances are known as compounds³.

Atoms can combine into compounds in two ways. In the first way, the atom of one element donates electrons to an atom of another element. The donator now has less electrons than protons and becomes positively charged. The recipient ends up with more electrons than protons and becomes negatively charged. Both the donor and the recipient are known as ions (the donor is called an cation and the recipient is called a anion⁴). Since unlike charges attract, donor and recipient atoms will stick to each other to form a new substance, often a crystal. This is how table salt (chemical name: sodium chloride) is formed: each sodium atom donates one electron to one chlorine atom⁵.

In the second way, groups of atoms will share electrons among themselves resulting in what is called covalent bonding. The sharing of electrons causes the atoms in the group to stick together. Each group is called a molecule. Examples are water (hydrogen and oxygen) and carbon dioxide (carbon and oxygen)⁵.

Atoms of the same element can bind to each other as well. The atoms of non-metallic elements can form covalent bonds with each other. Seven such elements form diatomic (two-atom) molecules: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine⁶. In metals, the atoms in the metal give up their outer electrons to a sea of electrons that bathe the atoms; the electrons are no longer tied to a particular atom and can wander throughout the metal. It is this electron sea that binds the atoms together in the metal, and this bonding is knows as metallic bonding⁷.

Each atomic element has its valence number, the maximum number of atoms with whom an atom of that element can bond⁸. Hydrogen has a valence number of 1 — it can only bond with one other atom at a time. Oxygen has a valence number of 2; it can bond with two atoms. Nitrogen has a valence number of 3, carbon has a valence number of 4. Helium does not bond with other atoms, so its valence number is 0.

Although many molecules are electrically neutral having no net charge, one end of such a molecule can have a positive charge, the other end can have a negative charge. This happens when the electrons in the molecule are spending more time in one atom than they are in another. When this happens, the molecule is called a dipole. Some dipoles are permanent because one atom is attracting electrons more strongly than the others⁹. Other dipoles are temporary, the result of statistical fluctuations where one atom for a split second just happens to have more electrons about it than the others¹⁰. Dipoles give rise to the intermolecular forces that bind molecules together in a solid or in a liquid¹¹. Breaking these intermolecular forces (as occurs during melting and boiling) requires the extra energy known as latent heat. More about latent heat in coming posts¹².

Molecules can exist by themselves or they can become ions (that is, have a net charge), in which case they are referred to as polyatomic ions or molecular ions¹³. An example of this is the fertilizer and explosive ammonium nitrate. It consists of two ions: the ammonium ion, which is the ammonia molecule with an extra hydrogen atom, and the nitrate ion, which is the nitrogen dioxide molecule with an extra oxygen atom¹⁴. Like atomic ions, molecular ions have valence numbers. Both ammonium and nitrate both have a valence number of 1. Carbonate and sulfate both have a valence number of 2¹⁵.

It is interesting that some of the properties that apply to atoms apply as well to molecules. Some atoms are self-contained and electrically neutral. They have little to do with the atoms around them and do not form compounds easily. These are the atoms of the so-called noble gases: helium, neon, argon, xenon, krypton, and radon¹⁶. Likewise, some molecules are self-contained and electrically neutral. They also do not enter easily into reactions with other chemicals around them. Carbon dioxide is an example¹⁷.

At the other end of the spectrum, there are atoms that, although electrically neutral, jump at the chance to react with other atoms. Sodium, potassium, fluorine, chlorine, are good examples of such atoms, to the extent that it is impossible to find these atoms by themselves in their electrical neutral state in nature¹⁸. Likewise, there are electrically neutral molecules that are extremely reactive: the hydroxide molecule for one. These atoms and molecules are known as free radicals¹⁹.

We have seen that both atoms and molecules can exist as ions, carrying a net electrical charge, and that these ions are attracted to ions of the opposite charge. Carbonate, nitrate, and sulfate are examples of negative molecular ions. They combine with positive ions to form such compounds as calcium carbonate, magnesium nitrate, and potassium sulfate²⁰.

Molecules can even form parts of larger molecules. A fine example are the numerous protein molecules in your body. Each protein is made up of smaller molecules called amino acids, strung together in an exact order to form the building blocks and the molecular engines of living cells²¹.

The branch of chemistry that studies carbon-based compounds is called organic chemistry. Organic molecules tend to be much larger than inorganic molecules. Most inorganic molecules do not consist of more than a dozen atoms; organic molecules can consist of thousands of atoms²². A large part of organic chemistry is the study of parts of molecules that tend to give compounds certain specific characteristics, such as alkene, alcohol, ketone, and ester, called functional groups²³. Is it possible to consider a functional group to be a molecule within a molecule? In other words, a molecule that plays the role of an atom within a larger molecule?

Footnotes

1. Georgia State University, Department of Physics and Astronomy, Hyperphysics website, section “Atoms and Elements”. To view, click here. There are actually 118 elements; you can see this on any up-to-date periodic table or by consulting Jefferson Lab’s It’s Elemental website. Four of 118 elements are as yet confirmed — see Wikipedia’s article Timeline of chemical elements discoveries, and scroll down to the section “Unconfirmed discoveries.” This leaves 114 elements confirmed by science. Of these 114 elements, only 91 occur naturally. 23 elements (including technetium, element 43) must be synthesized by humans and last minutes at most before disintegrating into simpler elements.
2. The Free Dictionary website. Chemical Element. To view, click here. Note that the definition claims there are 92 naturally-occurring elements. There are only 91. They forgot that technetium (element 43) does not occur naturally.
3. Chemicool website. Definition of Compound. To view, click here.
4. Note on pronunciation: “Cation” does not rhyme with “nation”, it is pronounced cat-eye-on. “Anion” does not sound like “onion”, it is pronounced an-eye-on.
5. University of California at Davis ChemWiki website. Ionic and Covalent Bonds. To view, click here.
6. Princeton University website. Diatomic molecules. To view, click here. Examples of non-diatomic covalent bonds among non-metals include the allotropes of carbon (graphite, diamond, buckyball) and phosphorus (white, red, violet, black)
7. University of California at Davis ChemWiki website. Metallic Bonds. To view, click here.
8. Frostburg State University General Chemistry Online website. What is the difference between valence, and number of valence electrons? To view, click here.
9. Utah Valley University OChemPal website. Dipole Moment. To view, click here.
10. Master Organic Chemistry website. The Four Intermolecular Forces and How They Affect Boiling Points. To view, click here, then scroll to section 4: “Van der waals Dispersion forces (London forces)”.
11. Master Organic Chemistry website. The Four Intermolecular Forces and How They Affect Boiling Points. To view, click here.
12. This post is not ready yet.
13. Frostburg State University General Chemistry Online website. Polyatomic Ions. To view, click here.
14. Princeton University website. Ammonium Nitrate. To view, click here.
15. Helmenstine, Anne Marie. About.com Chemistry website. List of Common Polyatomic Ions. To view, click here.
16. University of California at Davis ChemWiki website. The Noble Gases. To view, click here.
17. The Columbia Electronic Encyclopedia, published on the Infoplease website. Carbon Dioxide. To view, click here.
18. Sodium and potassium are alkali metals, chlorine and fluorine are halogens. For alkali metals, see Bentor, Yinon, Periodic Table: Alkali Metals. ChemicalElements.com website. To view, click here. For halogens, see the Purdue University website Bodner Research Website, The Chemistry of the Halogens. To view, click here.
19. Australian Research Council, ARC Centre of Excellence for Free Radical Chemistry and Biotechnology website. What Are Free Radicals? To view, click here.
20. General Certificate of Secondary Education science website. Atomic Structure. To view, click here.
21. Bailey, Regina, Amino Acid. About.com Biology website. To view, click here.
22. Personal observation.
23. Fromm, James Richard, The Concept of Functional Groups. Third Millenium Online Website. To view, click here.

It was the 6th century B.C. Greek philosopher and scientist Thales of Miletus who discovered an interesting phenomenon when one rubbed amber (a fossilized secretion of ancient trees) with fur: the amber could attract light objects such as straw¹. In modern parlance, we would say that the both the amber and the straw were electrically charged. No one knows what electric charge actually is or why it exerts force on other charges around it². We can only study its behavior.

Scientists in the 18th century sought to explain why electrically charged objects not only attracted but also repelled one another; they posited two types of electric charge — positive and negative. Two objects with like charge (positive and positive, or negative and negative) repelled each other. Two objects with unlike charge attracted each other³.

Much later it was found that electric charge could be traced to the atom itself. Protons are all positively charged, electrons are negatively charged, and neutrons have no charge. All protons and electrons have the same absolute amount of charge, so an atom with the same number of protons and neutrons is electrically neutral⁴.

When objects having electric charge are at rest, they radiate simple electric fields, which act on other electric charges resembling the way gravity acts on mass. Like the gravitational pull between two masses, the electrical force between two electric charges at rest is inversely proportional to the square of the distance between them. If you move two charges closer together so that the distance between them becomes only a third of what it was, the force between them will increase nine-fold⁵.

Interesting things happen when charges move. Our civilization depends on electric current, which usually consists of free electrons traveling through electric wires forming rivers of electricity⁶. Electric currents generate a second force called the magnetic force, a force that attracts or repels other electric currents⁷. Whenever moving charges speed up, slow down, or change direction, they generate waves in the electric and magnetic fields around them. These waves, known as electromagnetic radiation, form such familiar phenomena as radio waves, visible light, and X-rays⁸. More about electromagnetic radiation in a later post.

Footnotes

1. Watkins, Thayer. The Economic History of Amber, San Jose State University website. To view, click here.
2. Shpenkov, George P., What the Electric Charge Is. To view, click here.
3. This began with the work of the French chemist Charles François du Fey (1689 – 1739) and the American scientist Benjamin Franklin (1706 – 1790). The work of these two men are neatly summarized by the Center for Integrating Research + Learning on the National High Magnetic Field Laboratory website Magnet Lab. Click here to view their summary of Du Fey’s work (starting from the fifth paragraph) and here to view their summary of Franklin.
4. Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “Protons, neutron & electrons”. To view, click here.
5. Hyperphysics website, Department of Physics and Astronomy, Georgia State University, section “Coulomb’s Law”. To view, click here.
6. Hyperphysics website, Department of Physics and Astronomy, Georgia State University, section “Electric Current”. To view, click here.
7. Rensselaer Polytechnic Institute website. Introduction to Magnetism and Induced Currents. To view, click here.
8. Caltech university website. Electromagnetic field of an accelerated charge. To view, click here.

The science of climate is all about the substances that make up our planet: the land, the oceans, the atmosphere, the atmospheric gases that influence climate. All these things are made up of atoms, ions, radicals, and molecules, governed by the laws of chemistry and physics. To understand their behavior, we really need to understand atoms and molecules, and that is where our physics primer begins.

It was the ancient Greeks¹ and Indians² who first suspected that all matter was composed of tiny particles called atoms, but scientific confirmation did not come until the 19th century when the English chemist John Dalton (1766–1844) noticed that substances that combine with each other in chemical reactions always combine in exact ratios (for example, two parts hydrogen always combines with one part oxygen to form water). The only way to explain this was to hypothesize that matter was made up of discrete particles that combined in exact ratios³.

In 1909, two English physicists Geiger and Marsden under the direction of the New Zealand-British physicist Ernest Rutherford (1871–1937) ran an experiment in which they shot tiny positively-charged atomic particles called alpha particles through a gold foil and measured their deflections. Most particles were not deflected at all. A few were deflected a couple of degrees. But a handful were deflected 90° or more. This led Rutherford to conclude that most of the volume of the atom is empty space, with its mass and positive charge concentrated in a very small center called the nucleus⁴. The nucleus is surrounded by much smaller particles, discovered earlier in 1897 by the British physicist J.J. Thompson (1856–1940)⁵, called electrons that buzz about the nucleus like gnats on a summer day⁶. Each electron is about 1/1836 of the mass of a proton⁷.

The nucleus itself is composed of two types of particles: protons⁸ and neutrons⁹. Protons and neutrons have about the same mass (the neutron is slightly heavier)¹⁰, but the number of protons determines an atom’s element whereas the neutrons just add mass¹¹. The number of electrons flying around the nucleus determines the atom’s current chemical state¹². For example, an atomic nucleus might consist of eight protons, ten neutrons, and be surrounded by eight electrons. The eight protons identify the atom as oxygen, the ten neutrons make it heavier than average for an oxygen atom (most oxygen nuclei have only eight neutrons), and eight electrons make the atom electrically neutral but quite ready to react with other atoms.

Footnotes

1. Stanford Encyclopedia of Philosophy website, Ancient Atomism, 2005. To view, click here.
2. Keith, Arthur Berriedale. Indian Logic and Atomism: An exposition of the Nyäaya and Vaicesika Systems, 1921. See Chapter 8: The Philosophy of Nature, p. 208. Viewable at the University of Toronto Libraries website. To view, click here.
3. Childs, Peter E., John Dalton. Chemistry Explained website. To view, click here.
4. University of South Florida website. The Gold Foil Experiment. To view, click here
5. Chemical Heritage Foundation website. Joseph John Thompson. To view, click here.
6. Contemporary Physics Education Project (CPEP), Nuclear Science — A Guide to the Nuclear Science Wall Chart, chapter 2. Lawrence Berkeley National Laboratory website. To view, click here.
7. Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “Protons, neutron & electrons”. To view, click here.
8. Hyperphysics website, Department of Physics and Astronomy, Georgia State University, section “Proton”. To view, click here.
9. Hyperphysics website, Department of Physics and Astronomy, Georgia State University, section “Neutron”. To view, click here.
10. Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “What does an atom look like?”. To view, click here.
11. Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “How many electrons, protons, and neutrons are contained in an atom?”. To view, click here.
12. Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “How does the structure of an atom relate to its properties?”. To view, click here.

To be able to discuss environmental issues intelligently, you don’t have to have a deep science background. But to understand what is happening on a fundamental level, you really do need to know the science. Some time ago, I decided that for my next blog topic, I would tackle the subject of climate change from a scientific perspective. I am writing for a wide, general-interest audience, and I have no idea how familiar my readers are with the scientific principles I want to discuss. (I’m not a professional scientist myself, and my own scientific knowledge leaves a lot to be desired.) I therefore decided to write a physics primer where those readers who lacked a science background could fill themselves in with what they needed to know, and to which I could refer when I discussed a scientific concept that might not be familiar to everybody.

The project proved far more involved than I ever thought it would be. I thought I would just scribble a few posts and be done with it. I’ve ended up so far with 21 posts, and I’ve only finished six of them (not counting this one). I started in January 2014, it is now July, and I am far, far from finishing. I thought I’d better publish what I have now or it would be a long time before I’d have new material on my blog.

These first six posts are a review of the physical and chemical principles behind the existence of matter: atoms, molecules, ions, charge, mass, how to write chemical formulas and equations. Later posts will discuss energy, heat, and Earth’s climate system.

If you came here via a link, you can navigate between posts by clicking on the arrows that appear above the post heading. The right arrow (→) always points to the next post; the left arrow (←) always points to the previous post. In this particular post, the right arrow is labeled A Physics Primer 1: The Atomic Nature of Matter and points to the next post. The left arrow is labeled Welcome to the Environmental Analyst and points to the home page (that was unintentional, it just worked out that way). To return to the home page of the blog from any blog post, click the “Home” tab at the top of the page.

The posts are heavily footnoted. They don’t necessarily show where I got my information, but they do show that what I write has a basis. I also include additional information and observations in the footnotes, so if you have the time, check them out.

At the time of this writing, July 11, 2014, I have not had my posts reviewed by a professional scientist, so the chances are higher that I included some erroneous information. Be aware of this and don’t hesitate to challenge me if something I wrote doesn’t seem right to you.

While I do hold strong views on environment topics, this part of the discussion should be free of any partisan bias. If you find any, or if you have any other comment, please let me know. Feel free to type your comment on the bottom of the post, or send an email to mhkblogs@gmail.com . All constructive criticism is most welcome!