1. Note Guide 2-2 day 2 4. Atomic Mass – an average of all the elements isotopes (different # of neutrons compared to protons) Classes of Elements – 3 main classes: 1. Metals – majority of the elements --good conductors of electricity --solid at room temp --most are malleable (can be shaped) --most are ductile (drawn into thin wires)

2. --found left of the stair case Transition metals = elements in groups 3-12 --form a bridge between elements on the left side and right side of the table --can have more properties in common than elements in other groups

3. --common metals: mercury, aluminum, copper, nickel, iron, magnesium 3. Nonmetals – to the right of the stair case --poor conductors of electricity/heat --many are gasses at room temp. --physical/chemical properties vary greatly

4. --common nonmetals: flourine (most reactive) Sulfur, oxygen, helium 3. Metalloids – the elements that form the stair case --fall between metals and nonmetals --share characteristics of both metals and non metals --common metalloids: silicon, Arsenic Variation across a period – properties within a period change in similar ways from left to right --across a period (from L to R) the elements become less metallic and more non-metallic in their properties.