• "rock cycle" - generates the three basic rock types of the Earth's crust

• eight elements comprise 99% of the Earth's crust

• two of these elements - oxygen & silicon - account for 74% of the Earth's crust

• a "mineral" - an element or combination of elements that forms an inorganic, naturally occurring, solid

• a mineral has a definite chemical composition, and must have an orderly internal structure (i.o.w., a crystalline structure)

• 4,000 minerals - only 20 are common - 10 of the 20 make up 90% of the minerals in the crust

• a "rock" - an assemblage of one or more minerals bound together; the properties of the individual minerals are retained - thousands of rock types

• all rocks form from one of the following 3 processes: igneous, sedimentary, and metamorphic processes

Rocks are Aggregates of One or More Minerals

A. The Elements & the Periodic Table

• 19th-century scientists discovered that all substances could be formed by using only 92 basic building blocks called elements: the basic building blocks of minerals

• Today, over 100 elements are known - although some have been produced only in the lab

• most minerals are a combination of two or more elements, joined (bonded) to form a compound; (some minerals are made from just one element)

• The elements were arranged into a Periodic Table by Dimitri Mendelev about 1870.

• The elements were organized in such a way that their properties, similarities, and differences could be predicted from their position on the table.

• Each element has a name and is abbreviated with a 1 or 2 letter symbol. E.g., H for hydrogen; He for helium; and O for oxygen.

• Each element has its own box on the table. Elements in the same columns have similar chemical behavior.

• Each element (box) has an atomic number and an atomic mass.

* Atomic Mass (atomic wt)= the mass of the atom. (Results from protons and neutrons which reside in the atom's nucleus.)

• The elements are made up of individual units called atoms - the smallest part of matter that still retains the characteristics of an element

    Periodic Table of the Elements

B. Atomic Structure

- The Nucleus: contains 99.9% of an atom's mass. Is comprised primarily of protons and neutrons.

- Protons: have a positive electrical charge of +1; and weigh roughly the same as neutrons. (The # of protons that an atom has determines its atomic #.)

- Neutrons: no electric charge. Contribute to an atom's mass. In most atoms there are approximately equal #s of protons and neutrons.

• Atoms with nuclei that contain different #s of neutrons are called isotopes. (E.g., carbon 14, carbon 12

• Moving around the nucleus in various "orbits" (called shells or energy levels) are a cloud of light, negatively charged electrons.

• electrons can orbit only in certain well-defined paths, and can never be found anywhere else.

• Each orbital has a certain specifc amount of energy associated with it; so the energy of atomic electrons can only have certain exact, specified values.

• Electrons move from one orbital to another by means of a "quantum leap".

• An electron moving to an orbital farther from the nucleus must take in energy (by absorbing light or colliding with another atom).

• Conversely, an electron moving to an orbital closer to the nucleus must give-up energy by emiting electromagnetic radiation.

Models of the Atom

- (Recall: like charges repel and unlike charges attract.)

- Question: what is that holds materials together?

- Answer: "electrostatic charge" ( the attraction of positively charged objects for negatively charged objects draws materials together).

• It is this attractive force that holds or "bonds" these materials together. We say that a "chemical bond" has formed.

• when two or more elements have bonded together in definite proportions, a "compound" has been formed

• When two atoms bond they try to "reach a state of lowest possible energy". This is accomplished by "filling-up" the electron shells; with the lower most shells being filled-up first.
• the first principal shell (k-shell), holds a maximum of 2 electrons, while each of the higher shells holds 8 or more electrons
• the outermost shell (with the exception of the first shell), however, can hold no more than 8 electrons
• the outermost shells are usually involved in bonding; & would like to have a full compliment of electrons ("octet rule") - to become stable
• to satisfy the octet rule, atoms may either gain, lose, or share electrons with one or more atoms

- one atom gives-up an electron; and the other receives that electron (permanently).

- so now you have a positively charged ion (cation) and a negatively charged ion (anion).

- the attractive force between the two oppositely charged ions holds (bonds) them together.

- in the case of sodium (Na) and Chlorine (Cl), Na has 1 extra electron, Cl one too few; so, Na gives its electron to the Cl to make NaCl (sodium chloride, table salt).

- both atoms now have full orbitals; they have reached their lowest energy state.

- the Na is now positively charged, having given-up and electron - while the Cl is negatively charged, having received the extra electron. The attractive electrostatic force holds them together.
 
 

2. The Covalent bond:

- the outer electrons between two atoms are "shared".

- results when the outer shells of adjacent atoms are both half filled.

- the electrons in the outer shells rapidly travel between the adjacent atoms and act to fill both shells.

- covalent bonds are the bonds that hold your body tissue and DNA together. They are very common in nature.
 

3. Metallic Bonds:

- are involved in the bonding of metal compounds.

- the atoms of metals (gold (Au), iron (Fe), aluminum (Al), etc.) typically have filled outer shells plus one or more extra electrons.

- after two metals combine these extra electrons (neg. charges) move throughout the material freely, while the protons in the nuclei create centers of positive charge. The resulting attractive forces between the flowing electrons and the positive nuclei hold the metal compound together.
 

D. Isotopes & Radioactivty

• while the isotopes of most elements are stable (do not decay); the isotopes of some elements do decay naturally through a process called "radioactivity"
• a decaying atom emits particles and energy - this occurs when the forces that bind together the nucleus are not strong enough to hold it together
• the rate at which a nucleus decays is steady and determinable
• this (along with other information about the "parent" and "daughter" material) makes radioactive isotopes useful for dating materials and geologic events