Elements, Compounds, and Mixtures

What is a Pure Substance? A pure substance is composed of a single type of material  elements & compounds Examples: water, diamond, gold, table salt, bronze Pure substances cannot be separated by physical means (distillation, filtration, and chromatography)

What is an Element? We have already studied elements An element is a pure substance containing only one kind of atom As of now, 118 types of elements are listed and classified on the Periodic Table Examples?

What is an Element? Elements are always homogenous – the composition is identical wherever you sample it, uniform all the way through in composition and properties An element cannot be separated into simpler materials

What is a Compound? A compound is a pure substance that is created by 2 or more kinds of atoms The atoms are chemically combined by reacting with one another, forming molecules Examples: NaCl, H2O, CO2, NH3, NaHCO3, and C6H12O6 Compounds cannot be separated by physical means without a chemical reaction

Why Do Compounds Form? Elements will form compounds to become more stable. Na is flammable in water Cl2 is a toxic gas NaCl is a very stable compound that is neither flammable nor toxic Properties of a compound are usually different than the properties of the elements it contains Compounds that are unstable will break down to form more stable elements

Why Do Compounds Form? Compounds form when valence electrons in the outermost shell of 2 or more elements interact THE OCTET RULE: an element is most stable with 8 valence electrons Elements will join chemically to get 8 valence electrons

Example: CO2 Oxygen (O) has 6 valence electrons Carbon (C) has 4 valence electrons If carbon shares 2 electrons with each oxygen, everyone will have 8 valence electrons!

*REMEMBER: solution = solute + solvent* What is a Mixture? A mixture is the physical combination of 2 or more elements or compounds – NOT chemically combined (no reaction between substances) Mixtures can be evenly distributed or not: uniform (homogeneous) = solutions non-uniform (heterogeneous) *REMEMBER: solution = solute + solvent*

What is a Mixture? The properties of a mixture are similar to the properties of its components Ex: Salt water NaCl = salty H2O = clear liquid Salt water = clear, salty liquid! Mixtures can be separated by physical means (filtration, distillation, and chromatography)

Homogeneous Mixtures: Heterogeneous Mixtures: EXAMPLES! Homogeneous Mixtures: Heterogeneous Mixtures: Rain Steel Air Vinegar Salt water Whipped cream Cereal Ice in soda Soil Pizza Box of toys You

Classifying Matter… Matter Pure Substances Mixtures milk, tea Fe, O Elements Compounds Homogeneous Heterogeneous Rocky Road ice cream, muddy water milk, tea Fe, O H2O, CO2