Chapter 2 Atomic Theory and Atomic Structure

Chapter 2 Atomic Theory and Atomic Structure - Chapter 2...

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Chapter 2 Atomic Theory and Atomic Structure 2.1 Atomic Theory of Matter Postulates of Dalton’s Atomic Theory – An explanation of the structure of matter in terms of different combinations of very small particles. 1. All matter is composed of indivisible atoms. a. Atom is an extremely small particle of matter that retains its identity during chemical reactions 2. An element is a type of matter composed of only one kind of atom, each atom of a given kind having the same properties. Mass is one such property. Thus, the atoms of a given element have a characteristic mass. 3. A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions. The relative numbers of any two kinds of atoms in a compound occur in simple ratios. 4. A chemical reaction consists of the rearrangement of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction. Atomic Symbols – one- or two- letter notation used to represent an atom corresponding to a particular element. Law of Multiple Proportions – when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in ratios of small whole numbers. 2.2 Structure of the Atom Nucleus – atoms central core – positively charged and contains most of the atom’s mass, and one or more electrons. Electron – very light, negatively charged particle that exists in the region around the atom’s positively charged nucleus. 2.3 Nuclear Structure; Isotopes Atomic Number – each element has a unique nuclear charge that is an integer multiple of the magnitude of the electron charge. The number of protons in the nucleus of an atom. Proton – nuclear particle having a positive charge equal to that of the electron and a mass more than 1800 times that of the electron. Element – Substance whose atoms all have the same atomic number.
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Neutron – Nuclear particle having a mass almost identical to that of the proton but no electric charge. Mass Number – Total number of protons and neutrons in a nucleus. Nuclide – Atom characterized by a definite atomic number and mass number. Nuclide Symbol for Sodium: Mass Number -------- 23 Na Atomic Number ------ 11 Isotopes – atoms whose nuclei have the same atomic number but different mass numbers; that is, the nuclei have the same number of protons but different numbers of neutrons. Sodium has one known isotope called Sodium -23. 2.4 Atomic Masses Dalton found the average mass of one atom relative to the average mass of another Atomic Mass Unit – A Mass unit equal to exactly one-twelfth the mass of a carbon-12 atom. Atomic Mass – The average atomic mass for the naturally occurring element, expressed in atomic mass units.
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