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Chemistry Topic A-C Review

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Western University
Chemistry 1027A/B
Kay Calvin

Chemistry 9/12/2012 9:12:00 AM Topic A: Atoms, Molecules, and Moles A1: Atoms Atoms  Atoms are the building blocks, o Protons, neutrons, and electrons  Protons and neutrons have almost the same mass (each has a mass almost equal to one atomic mass unit [amu])  Electron is only about 1/2000thof the mass of a proton or neutron Atomic Number  All atoms of the same element have the same number of protons in the nucleus Mass Number  The mass number is the total number of protons and neutrons in an atom  Mass number = number of proton + number of neutrons Isotopes  Same number of protons but different number of neutrons therefore different mass number  Same atomic number but different mass number  Isotopic abundance is the percent by number of each of the isotopes of an element Isotopic abundance and average atomic mass  average atomic mass = {SUM} [percent isotopic abundance ]X isotopic mass [ 100 ] Atomic Mass Standard  The atomic mass standard is based on the mass of C-12  The atomic masses of all other elements in the periodic table have been measured using c-12 mass as exactly 12 u  One atomic mass unit is defined as exactly 1/12 the mass of a c-12 atom Ions  Z is also the number of electrons in a neutral atom  Positively charged ion is a cation  Negativity charged ion is a anion  Ion: atom or group of atoms that have gained or lost electrons A2: Molecules and Complex ions  Molecules are atoms bonded together in a specific ration  A compound is a molecule containing more than one element  A molecule with only two of the same atoms is called diatomic  A molecule with more then one type of atom is called poluatomic The Mole and Avogadro’s number  One mole is defined as the number of atoms in exactly 12 grams of pure carbon 12  Avogadro’s number Na = 6.02 X10^23  Moles are represented by an n  One mole of anything would be 6.02 X10^23 of those things  # moles = mass / Molar mass  (number of moles of atoms) X (Avogadro’s number) = number of atoms A.3 Mass, Molecular Mass, and Molar Mass  The mass of one molecule is the sum of the masses of all the atoms in the molecule and is called the molecular mass  The mass of one mole of molecules is called molar mass (MM)(g/mol) Mass Percent Mass percent = mass of one species X100
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