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| Law of Definite Composition |
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| A compound always contains the same elements combined in the same proportions by mass. e.g. H2O is 88% oxygen no matter where it is found. |
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| The number of protons plus neutrons in the nucleus of an atom. |
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| Atoms which contain the same number of protons but different numbers of neutrons. e.g. hydrogen has three isotopes with mass numbers of 1, 2, 3. |
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| A group of two or more atoms held together by chemical covalent bonds |
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| An atom or group of atoms having a positive or negative electrical charge. e.g. Na+, Cl-, SO42- |
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| Law of Conservation of Mass |
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| During a physical change or reaction, or a chemical reaction, matter is neither created nor destroyed. |
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| The electrons found in the outermost energy level of an atom |
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| A number, positive or negative, representing the charge on an ion, or the distribution of electrons in an atoms involved in a chemical bond. |
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| The mass of a proton or neutron is equal to one atomic mass unit. symbol is amu 1 amu = 1.66 X 10-24 g |
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| Three postulates of Dalton's Atomic Theory |
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Definition
1. An element is composed of identical atoms.
2. Atoms of different elements have different properties. 3. Compounds are atoms of two or more elements chemically combined. |
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| positively charged ion: Na+, Fe2+, NH4+, Ag+ |
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| negatively charged ion: Cl-, OH-, P3- |
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| Neutron: Location in atom |
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| Electron: Location in atom |
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| electron cloud surrounding the nucleus |
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| 1/1837 amu (sometimes expressed as zero) |
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| Number of protons in the nucleus of an atom of an element. |
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| Describe the research of: Rutherford |
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| Nucleus. Gold foil experiment. Found positively charged atomic nucleus. 1911 |
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| Describe the research of: Millikan |
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Definition
| Electron. Oil drop experiment. Calculated the electric charge and the mass of an electron. 1909 |
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| Describe the research of: J.J. Thomson |
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| Electron. Cathode ray tube experiment. Identified electron paths in cathode ray tubes. 1897 |
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| Law of Multiple Proportions |
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Definition
| The same elements may combine to form more than one compound. The ratios of atoms are in small whole numbers. Proposed by Dalton. e.g. H2O and H2O2 |
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| Which elements exhibit several oxidation states, and why? |
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| The transition elements. Their highest energy sub-levels are close in energy (s and d) and easily become involved in bonding. |
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