2 Chemical CompoundsA compound is when 2 or more elements chemically combine.They are formed by chemical bonds between atoms.The properties of a compound are often very different from the elements themselves.
3 Chemical FormulasFormulas that use chemical symbols and numbers to represent what makes up a substance.Examples:NaCl – Sodium chloride (salt)Na – Sodium, Cl - ChlorineH2O – Dihydrogen monoxide (water)H – Hydrogen, O - OxygenCO2 – Carbon dioxideC – Carbon, O - Oxygen
4 SubscriptsNumbers written below and to the right of a chemical symbol in a formula.H2O – 2 Hydrogen, 1 OxygenTells how many atoms of an element are in each molecule.Only used if more than one atom is present.
5 Let’s Practice: C9H8O4How many atoms of each element are in this compound?C = Carbon – 9 atomsH = Hydrogen – 8 atomsO = Oxygen – 4 atomsHow many elements are there? How many total atoms?3 elements total atoms
6 H2SO4 How many atoms of each element are in this compound? H = Hydrogen – 2 atomsS = Sulfur – 1 atomO = Oxygen – 4 atomsHow many elements are there? How many total atoms?3 elements atoms
7 Coefficients # placed in front of a chemical symbol or formula Identifies the # of molecules of a substance2H2O = 2 molecules of H2O3FeO3 = 3 molecules of FeO3
8 Coefficients X Subscripts To determine the number of atoms using coefficients you multiply the coefficient with the subscript.Example:3H2O - 3 molecules of H2OH = 3 x 2 = 6 Hydrogen atomsO = 3 x 1 = 3 Oxygen atoms (remember: when there isn’t a subscript after the element, there is an invisible ‘1’)
9 Let’s Practice: 2Fe2O3 2 Molecules of Fe2O3 = 2 X 2 = 4 Fe (iron) atoms2 X 3 = 6 O (oxygen) atoms
10 Using ParenthesesMultiply the subscript outside the parenthesis with each element inside parentheses only.Example:Al2(SO4)3Al = 2 atoms of AluminumS = 3 X 1 = 3 atoms of SulfurO = 3 X 4 = 12 atoms of Oxygen
11 Let’s Practice: (CH3)2CHOH C = 2 x 1 = = 3 carbon atomsH = 3 x 2 = = 8 Hydrogen atomsO = only 1 Oxygen atom
12 Chemical ReactionsOccurs when one or more substances change to produce one or more different substances.Atoms are rearranged to form a totally new substance with properties that are completely differentIndicators of a chemical reactionGas formationSolid formation – precipitateEnergy change – light, heat, or soundColor change
13 Chemical EquationsUses chemical symbols and formulas to represent a chemical reaction.Example:2H2 + O2 → 2H2OReactants Yield ProductsSignElements are rearranged to form new substances
14 Chemical EquationsReactants – starting materials in a chemical reaction (left side)Products – substances formed in a chemical reaction (right side)
15 Let’s Practice: C12H22O11 + H2O → H2O + C12H22O11 Does this equation show the atoms rearranged to form NEW substances?Reactants = C12H22O11 and H2OProducts = C12H22O11 and H2ONo! No new substances have been formed.
16 Zn + 2HCl → ZnCl2 + H2Does this equation show elements rearranged to form new substances?Reactants = Zn and 2HClProducts = ZnCl2 and H2Yes! – New substances are formed.
17 Law of Conservation of Mass The mass of atoms and molecules is neither created nor destroyed in chemical reactions.The # of atoms for each element in the reactants must equal the # of atoms for each element in the products in a chemical reaction.Chemical Equations must be balanced.
18 Let’s Practice: CH4 + O2 → H2O + CO2 Is the equation above balanced? ReactantsCarbon = 1Hydrogen = 4Oxygen = 2NOT BALANCED!ProductsCarbon = 1Hydrogen = 2Oxygen = 3
19 YES! NaCl + AgNO3 → NaNO3 + AgCl Reactants → Products Na = 1 Na = 1 Cl = 1 Cl = 1Ag = 1 Ag = 1N = 1 N = 1O = 3 O = 3Is this equation balanced?YES!