Atoms

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Concerned about radioactivity in nature?

To keep things in perspective, consider that 0.01% of all potassium is radioactive K-40.

Potassium is an essential element in the human body.

If your body is about 1% K, this means a 70 kg

(150 pound) person contains around

1x1021 atoms (that’s one billion trillion atoms)

of radioactive K-40.

Slide 21

Chemical Bonds

One typical consequence of chemical reactions is the formation of chemical bonds between atoms and complexes.

What kind of bonds form is based on the electronic configuration of the atoms involved.

Atoms with near-full (halogens) and near-empty (alkalis/alkali earths) outer electron shells, as well as transition metals, may form ionic bonds.

Covalent bonds are where atoms share outer shell electrons.

The bulk of minerals are dominantly ionically bonded. However, many minerals have bonds with some covalent

and some ionic components.

Slide 22

Ionic Bonds

Atoms satisfy themselves by the give and take of outer shell electrons.

Most minerals are held together by primarily ionic bonds.

Slide 23

Covalent Bonds: Electron Sharing

These carbon atoms are held together by sharing outer-shell electrons.

Slide 24

Alternative Bonds

Some minerals have metallic bonds,

which are a form of covalent bonds.

One notable weak kind of bond is called the

Van der Waals force, essentially an ionic bond.

When we talk about minerals we will see that these bonds are responsible for the key

physical properties of some minerals.

Slide 25

Chemical Reactions: Achieving Stability

Chemical reactions take place in order to achieve a more stable state (lower total energy) under given conditions (pressure, temperature).

Unstable reactants react to form stable products.

[don’t get confused: we’re not talking about nuclear instability here]

To complicate this, the transition from unstable mineral to stable mineral is not necessarily automatic.

Many chemical reactions require

a great deal of energy

to run to completion.

Slide 26

What is a Mineral?

naturally occurring

inorganic compound

specific chemical composition

defined crystal structure

consistent physical properties

Slide 27

Stability

With sophisticated furnaces and presses, we have investigated what chemical compounds (minerals) are stable at given pressures and temperatures