Elements and Compounds

Elements Element—simplest form of matter with unique set of properties. Element—simplest form of matter with unique set of properties. Cannot be broken down into more simple units Cannot be broken down into more simple units Example: Hydrogen, Oxygen, Carbon symbolized by letters in the periodic table Example: Hydrogen, Oxygen, Carbon symbolized by letters in the periodic table H, O, C H, O, C

Compounds Mixed molecules made of two or more elements chemically combined in a fixed proportion. Mixed molecules made of two or more elements chemically combined in a fixed proportion. Compounds can be broken down into simpler substances (elements) using chemical Rx. Compounds can be broken down into simpler substances (elements) using chemical Rx. Example Water: H2O can be broken down into Hydrogen and Oxygen gas (electrolysis) Example Water: H2O can be broken down into Hydrogen and Oxygen gas (electrolysis)

Breaking Compounds physical methods (cutting, filtration, distillation) do nott work physical methods (cutting, filtration, distillation) do nott work To break down compounds, chemical change is needed. To break down compounds, chemical change is needed. Example: burning or oxidization reactions Example: burning or oxidization reactions

Breaking Compounds Properties of compounds are different than those of their component elements. Properties of compounds are different than those of their component elements. Example Example Compound NaCl (table salt): white crystals Na: sodium…soft metal Cl: chlorine…green poisonous gas

Breaking Compounds Electricity can be used to break down the compound water into hydrogen and oxygen. Electricity can be used to break down the compound water into hydrogen and oxygen. Oxidization can be used to break sugar (C6H12O6) into Carbon and H2O, CO2 Oxidization can be used to break sugar (C6H12O6) into Carbon and H2O, CO2

Distinguishing Substances and Mixtures Substance: Composition cannot by changed by physical means only by chemical means, compounds/elements Mixture: Composition of a material can be changed easily (filtration, destillation….) can homogeneous or heterogeneous Homogeneous mixtures cannot be easily distinguished from substances!!!!

Element Symbols Chemists use chemical symbols to represent elements Chemists use chemical symbols to represent elements First letter of a chemical symbol is always capitalized. First letter of a chemical symbol is always capitalized. If 2 nd letter is used, it is lowercase If 2 nd letter is used, it is lowercase C-Carbon C-Carbon Na-Sodium Na-Sodium Fe-Iron Fe-Iron Many symbols are from the language in which the element was first identified. Many symbols are from the language in which the element was first identified.

Formulas Chemists use chemical formulas to represent compounds Chemists use chemical formulas to represent compounds Subscripts in chem. formulas indicate the relative proportion of elements in a compound Subscripts in chem. formulas indicate the relative proportion of elements in a compound C 6 H 12 O 6 is glucose C 6 H 12 O 6 is glucose 6 Carbons, 12 Hydrogens, 6 Oxygens 6 Carbons, 12 Hydrogens, 6 Oxygens