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Chemistry in Quantitative LanguageFundamentals of General Chemistry Calculations$
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Christopher O. Oriakhi

Print publication date: 2009

Print ISBN-13: 9780195367997

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195367997.001.0001

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Atomic Structure and Isotopes

Atomic Structure and Isotopes

3 (p.33) Atomic Structure and Isotopes
Chemistry in Quantitative Language

Christopher O. Oriakhi

Oxford University Press

John Dalton proposed his theory of the atom in 1808 based on experimental data and chemical laws known in his day. The theory states that: 1. All chemical elements are made up of tiny indivisible particles called atoms. 2. Atoms cannot be created or destroyed. Chemical reactions only rearrange the manner in which atoms are combined. 3. Atoms of the same element are identical in all respects and have the same masses and physical and chemical properties. Atoms of different elements have different masses as well as different physical and chemical properties. 4. Combination of elements to form a compound occurs between small, whole-number ratios of atoms. Dalton’s theory resulted in the formulation of the law of conservation of mass and the law of multiple proportions. In a chemical reaction matter is neither created nor destroyed. The mass of products is equal to the mass of the reactants. If two elements form more than one compound between them, the masses of one element that combine with a fixed mass of the second element are in a ratio of whole numbers. Nitrogen and oxygen combine to form different compounds such as NO, NO2, and N2O. According to this law the number of nitrogen to oxygen atoms in these compounds should be a simple ratio of two small whole numbers. This is one of the basic laws of stoichiometry, as we shall see in chapter 9. An atom consists of a central nucleus, which contains roughly 99.9% of the total mass of the atom, and a surrounding cloud of electrons. The nucleus is composed of two kinds of particles, the protons and the neutrons, which are collectively known as the nucleons. The proton is positively charged while the neutron is electrically neutral. The electrons have a negative charge and surround the nucleus in “shells” of definite energy levels. (Note: energy level will be discussed in chapter 10.) In a neutral (unreacted) atom, the number of electrons is equal to the number of protons, so the atom has a charge of zero.

Keywords:   atomic number (Z), neutron, proton

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