Chemical Reactions describe chemical changes. Chemical Equations are shorthand descriptions of chemical reactions that use coefficients, symbols and subscripts to describe the ratios of a reaction. We call the substances before a reaction the reactants and we call the substances that are formed the products.
Antoine-Laurent de Lavoisier (1743-1794) is considered by many to be the father of chemistry. He was the first to clearly state the Law of Conservation of Mass. This states that matter is neither created nor destroyed in a chemical change. We can now add to that the idea that the atoms or building blocks of matter are simply rearranged in a chemical reaction.
John Dalton (1766-1844) took Lavoisier’s ideas further by developing the first basic atomic theory. He stated that an atom is the smallest unit of an element that can exist either alone or in combination with other atoms of the same or different elements.
His supporting evidence:
1. All matter is made up of very small particles called atoms.
2. Atoms of the same element are all chemically alike: atoms of different elements are chemically different.
3. Individual atoms of the same element may not have the same exact mass (isotopes), but for all practical purposes, they all have a definite average mass.
4. The atoms of different elements have different average masses.
5. Atoms are not subdivided in chemical reactions, they unite in simple ratios to form compounds.
He also developed the Law of Multiple Proportions. If two elements combine to form more than one compound, they will combine in distinct whole number ratios.
is the atomic mass/atomic weight the weighted average of the mass numbers of all isotopes of an element?
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