1. Selected topics Chapter 8 – Earth Chemistry All matter made of ATOMS Elements are substances with one kind of atom. There are 92 naturally-occurring elements. Listed in Periodic Table.

2. Nearly 99% of earth’s crust made of just 8 elements: Notice anything about these elements? Where are they in the periodic table? Why?

3. Notice that OXYGEN (O) AND SILICON (Si) make up about 75% of the crust. We will see that most minerals are “silicate minerals”, containing Si and O. These minerals make up the rocks of the crust. Granite – composed of several silicate minerals.

4. ATOMS Example:Carbon Atomic# 6 Mass# 12 Nucleus – 6 protons,6 neutrons Outside nucleus – 6 electrons

5. ISOTOPES Atoms of same element, but with different number of NEUTRONS, so different mass number. carbon-12carbon-14 6 protons 6 neutrons 6 electrons (not shown) 6 protons 8 neutrons 6 electrons (not shown) nucleus

6. We talk about isotopes because they are important in “dating” rocks and other materials (finding out how old they are). More on this later. Carbon-14 decaying and turning into nitrogen-14. The ratio of carbon-12 to carbon-14 can be used to tell how old something is.