Review
What are the three basic groups of rocks and how do they form?
What is the difference between a rock and a mineral
What is a Polymorph? A Pseudomorph?
What is the streak of a mineral?
What is the Mohs hardness scale?
How are cleavage and fracture different from each other?
What is Bauxite?
Chemistry and Mineral Properties
Different mineral properties are due to the chemical make up and bonding of
minerals.
Color of quartz: Why did the quartz samples you look at have different colors?
Why does a mineral have cleavage rather than fracture?
Why do some minerals react to acid
Elements combine to make minerals
Elements include…
Silica (Si)
Oxygen (O)
Hydrogen (H) etc…
Elements are made of atoms
Ex// An atom of silica
Atoms of elements bond together to form minerals
Quartz (mineral) made of Silica and Oxygen atoms bonded together
Basic Atomic Structure
3 particles make up atoms
Protons
Nucleus
+1 charge
Neutrons
Nucleus
neutral (no charge
Electrons
Outer shells
-1 charge
All atoms are neutral
What does this statement imply?
The structure of atoms
Center: Protons and Neutrons
Shells: Electrons
How electrons fill the shells is important
Controls how the atom will behave/bond
Rule that governs the filling of shells is known as the octet rule.
Octet rule
Defines how the electrons fill the shells
Atomic shells fill from the inside out
Determines if the atom has “a stable electron configuration”
If unstable will try to become stable through bonding with other elements
First shell
Shell closest to the nucleus
Only holds two electrons
Can hold less but not more
First shell must fill completely before any electrons go into the second shell
Second Shell
Second shell can hold up to 8 electrons
Before electrons go into the second shell the first shell must be full
The second shell must be full before any electrons will go into the third shell
Third shell has the same rules as the second shell
Before electrons go into the forth shell there must be 8 electrons in the third
This works up to about element #20
Octet Rule Summary
1st shell:
Will hold up to 2 electrons
Must be full before second shell starts to fill
2nd shell:
Will hold up to 8 electrons
Must be full before thirds shell starts to fill
3rd shell:
Will hold up to 8 electrons
Must be full before fourth shell starts to fill
Note: an atom is considered unstable if the outermost shell is NOT full
Example: Diagram a Lithium atom which has 3 protons, 3 electrons and 3 neutrons.
Is this a Neutral atom?
Is this a stable configuration?
Diagram a Fluorine atom which has 9 protons, 8 neutrons and 9 electrons
Is this a Neutral atom?
Is this a stable configuration?
Neutral but not stable
All atoms are neutral
Most atoms are not stable
The only atoms that are neutral and stable are the noble gasses (family VIII on
periodic table)
How can an atom become stable?
Atoms give up or take on electrons to fill their outer-most shell.
Lithium:
Neutral with 3 electrons but not stable
One electron in outermost shell
To become stable it gets rid of outermost electron
Is this now stable? Is it neutral?
Flourine: 9 Protons and 9 electrons
Is it neutral?
Is it stable?
How would it become stable?
Is it now neutral?
IONS
Created when an atom takes on electrons or gives up electrons
Charged particle…no longer an atom because it is charged!
POSITIVE CHARGE: more protons than electrons
NEGATIVE CHARGE: more electrons than protons
Atoms give up or take on electrons based on which requires the least amount of energy.
Ion with a positive charge is a CATION
Ion with a negative charge is an ANION
Exercise:
An atom has 5 protons and 6 neutrons
How many electrons does it have?
Diagram the atom
Will the atom become a cation, anion or remain an atom? If it becomes an ion
what will the charge be?
An atom has 12 protons, 12 neutrons and 12 electrons
Diagram the atom
Will the atom become a cation, anion or remain an atom? If it becomes an ion
what will the charge be?
Ionic Bonding
Stable and neutral compounds are created by joining cations and anions together
ex// Li+ and Fl- join to create LiFl
Ex// Na+ and Cl- join and create NaCl
This type of bonding is known as Ionic bonding
ions of opposite charges join together
Charge total must equal 0
Other ways to create stable elements?
Share electrons with another atom
Covalent bonding
Covalent bonding is created when atoms share electrons in the outer most shells
creates a molecule
Ex// Hydrogen has 1 electron
two hydrogen join by covalent bonding to complete the first electron shell
creates a hydrogen molecule
Covalent and ionic bonding creates stable and neutral molecules and compounds
Most minerals have covalent or ionic bonds or both
Why does the type of bonding between elements matter?
Bonding will control many of the mineral properties:
Cleavage occurs along ionic bonding planes
Fracture occurs where there is covalent bonding
Hardness of a mineral is controlled by bonding
How minerals grow:
Crystallize from nucleus
Add to the outside edge of the mineral
Depends on element available
Controls on mineral growth
Space
Lots of space will allow crystals to form well developed shapes
Cooling rate
Slowly cooling a melt create large crystals that interlock with each other
Rapid cooling a melt creates very small crystals