Download Quantity in Chemistry Unit 7 1 Atom is the simplest form of an

Quantity in Chemistry Unit 7 Atom is the simplest form of an element that represents that element. Each element has a unique symbol (ex: Fe) Atomic mass is the weighted average of the mass numbers of all the naturally‐occurring isotopes of that element Atomic element is an element that exists in nature as a single atom 
Fe, He, S, U, Cu... Diatomic element is an element that exists in nature as two atoms covalently bonded together 
There are only 7 (GEN – U – INE) – any element whose name ends in GEN or INE 
H2, N2, O2, F2, Cl2, Br2, I2 Molecule is one unit of a covalent compound or diatomic element (ex: H2O; Br2) Formula Unit is one unit of an ionic compound (ex: NaCl) Formula Mass of a molecule or formula unit is sum of all the atomic masses of the elements of which it is comprised Calculating Formula Mass 
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One molecule of H2O = 2xH + 1xO = (2x1) + 16 = 18amu One formula unit of NaCl = 23 + 35.5 = 58.5amu One molecule of Br2 = 80 + 80 = 160amu Mole is the “chemists’ serving” used to count only the extremely small particles that make up matter. The particles that make up a mole could be: 
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atoms (Fe) molecules (H2O or O2) formula units (NaCl) Avogadro’s Number is the number of particles in one mole ‐ It is exactly 6.02 x 1023 
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The number of atoms in one mole of atoms The number of molecules in one mole of molecules The number of formula units in one mole of formula units 1
Quantity in Chemistry Unit 7 Molar mass is the mass, in grams, of one mole of any substance  1 mole Fe = 56 g  1 mole H20 = 18 g  1 mole NaCl = 58.5 g Molar volume is the volume, in liters, of one mole of any gas at STP (std. temp & pressure)  1 mole He gas = 22.4 L  1 mole N2 gas = 22.4 L  1 mole CO2 gas = 22.4 L Solving Using Ratios – Cross Multiplication by Comparison 1) You will create a ratio that reflects the information and “ask” in the problem. How many moles in 150g of NaCl? 2) Create an equivalent ratio using either molar mass, molar volume or Avogadro’s number 150 58.5 1
3) Solve for X X = 2.56 mol NaCl Solving Using Ratios – EXAMPLES 1) How many molecules are in 5.5 moles of CO2? . .
X =3.31 x1024 molecules 2) How many moles are in 50L of N2? .
X = 2.23 moles 3) How many grams are in 3.8 moles of Al2(CO3)3? . X =889.2 grams Percent Composition The mass of each element in a compound compared to the entire mass of the compound and multiplied by 100 100 2