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CHAPTER 3: ATOMS AND MOLES By: John Pierce SECTION 1: SUBSTANCES ARE MADE OF ATOMS The law of definite proportions states that two of the same substances that have different sizes have the same proportions by mass. The law of conservation of mass states that mass can’t be formed or destroyed in normal chemical and physical changes. This law also states that the mass of the reactants in a equation equals the mass of the products. The law of multiple proportions states that when two elements merge to create two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers. SECTION 1: SUBSTANCES ARE MADE OF ATOMS Dalton’s Atomic Theory States 1. 2. 3. 4. 5. All matter is made up of atoms, which can’t be divided, created, or destroyed Atoms of a given element are identical in their physical and chemical properties. Atoms of different elements differ in their physical and chemical properties. Atoms of different elements to combine in simple, whole-number ratios to form compounds. In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed ,or changed. SECTION 2: STRUCTURE OF ATOMS The diagram to the left shows the parts of an atom. The nucleus is the center of the atom and houses the protons and neutrons. Protons have a positive charge whereas neutrons have a neutral charge. Shown in the outer field of the nucleus is the electron cloud, where electrons constantly move. Electrons have a negative charge. SECTION 2: STRUCTURE The picture to the left shows uranium isotopes. Isotopes are atoms of the same element that have different numbers of neutrons. OF ATOMS SECTION 3: ELECTRON CONFIGURATION Shown on the top are the shapes and orientations of the s and p orbitals, on the bottom are the different shapes and orientations for the d orbital. Each orbital that is shown can hold a maximum of two electrons. SECTION 4: COUNTING ATOMS The mass of atoms are expressed in Atomic mass Units or AMU. A mole is defined as the number of atoms in exactly 12 grams of carbon- 12. The number of particles present in 1 mole of a substance called Avogadro’s number (6.0221367 X 1023) WORK CITED Meyers, R. Thomas, et al. Ch 3, Pages 74-104 Holt Chemistry Austin, TX: Riehart and Winston, 2004.