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Chemistry 1027A/B
Felix Lee

General Review A: Atoms, Molecules and Moles -protons and neutrons make up most of the mass of an atom (m =m , mp+1/2n0m e- n -all atoms of the same element have the same number of protons in the nucleus -number of protons in an atom is the atomic number -mass number=#p +#n+ -the notation is often used to show both mass # and atomic # -X represents chemical symbol, A represents mass #, Z represents atomic # -atoms with the same number of protons but different number of neutrons are called isotopes -isotopes have the same atomic number but a different mass number -isotopic abundance is the % by number of each of the isotopes of an element -atomic mass assigned to each element on the periodic table is the average value of the masses of all the isotopes of that element (adjusted to show representation of each element) Average Atomic Mass= -the atomic mass standard is based on the mass of C-12, one atomic mass is defined as exactly 1/12 the mass of a C-12 atom -neutral atoms have an equal # of protons and electrons - -an atom that losses one or more electrons will have a positive charge equal to the number of e lost (becomes a cation) -an atom that gains one or more electrons will have a negative charge equal to the number of e - gained (becomes an anion) -ion is used for atoms that have gained/lost electrons -molecules are atoms bonded together in a specific ration -a compound is a molecule containing more than one element -complex ions are ions of molecules -a diatomic molecule has only two atoms, a polyatomic molecule has more than two atoms -one mole(n) is defined as the number of atoms in exactly 123 of pure C-12 -this # is called Avogadro’s number, N =A.02*10 -Avogadro’s number is used to determine the number of individual atoms, molecules or ions in a sample: (# of moles of atoms)*N =nAmber of atoms -to find the number of atoms in a sample of molecules or ions: (# of moles of molecules or ions)*N =# of molecules or ions A # of molecules or ions*# of atoms per molecule or ion=total # of atoms -mass of one molecule is the sum of all the atoms in the molecule, and is called the molecular mass -the mass of one mole of molecules is called the molar mass and the is the sum of all the atoms used in the molecule N(moles)=m(g)/MM(gmol ) -1 -mass percent=(mass of one species)/(total mass of sample)*100 -the value for a mass percent is always less than 100%, sum of all mass percents for all species involved will be 100% -mass percent can be used to find the empirical or simplest formula for a compound -empirical formula is the simplest ratio of the atoms in the molecule -molecular formula is some multiple of the simplest formula -the molar mass of the formula is used to determine the number of empirical “unit” in the molecular formula -the molecular formula must have an integral number of empirical formula “units” -mole fraction=(number of moles of one species)/(total number of moles) -mole percent= (number of moles of one species)/ total number of moles)*100% -sum of all the mole fractions of all species involved must be one -sum of the mole percents of all species involved must be 100% -the symbol X is used with a subscript of the element or compound to represent mole fractions -mass of one mole of a mixture has a specific ration of components -the relationship to find the average molar mass of a mixture (MM) is: MM=(X +MA )+(X AMM )B(X +MMB)+etC. C -this is the weighted average, the value of the average molar mass will be closer to the component present in the greatest quantity B: Solutions -solution is formed from a solid dissolved in a liquid -substance present in the smallest quantity (usually solid) is called the solute -substance present in the greatest quantity (usually liquid) is called the solvent -a solution can also be made of two liquids, through a process called dilution -most common unit of concentration is molarity (M) -molarity=[amount of solute(moles)]/[volume of solution (in litres)] or M=n/v -molarity must always be in moles/litre (not mn/mL) -deviations (usually negligible): -volume of a solution is affected by temperature (molarity may cha
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