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
- Stanford Encyclopedia of Philosophy website, Ancient Atomism, 2005. To view, click here.
- 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.
- Childs, Peter E., John Dalton. Chemistry Explained website. To view, click here.
- University of South Florida website. The Gold Foil Experiment. To view, click here
- Chemical Heritage Foundation website. Joseph John Thompson. To view, click here.
- 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.
- Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “Protons, neutron & electrons”. To view, click here.
- Hyperphysics website, Department of Physics and Astronomy, Georgia State University, section “Proton”. To view, click here.
- Hyperphysics website, Department of Physics and Astronomy, Georgia State University, section “Neutron”. To view, click here.
- Ohio State University Department of Chemistry and Biochemistry website. Atomic Structure, section “What does an atom look like?”. To view, click here.
- 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.
- 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.
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