Earth Chemistry

1
Earth Chemistry

• What are the basic components of the earths
  crust?
• Rocks?
• Soil?
• Minerals?
• Dead stuff?
• Compounds?
• Molecules?
• Salt?
• Elements?
• YES to all!

We will learn about the smallest type of matter
which will help us understand the nature of
things like rocks and minerals.
What is one of the smallest pieces of matter?
2
Elements and Atoms

• What is an element?
• A pure substance that cannot be broken down into
  simpler components by chemical and physical
  means.
• Examples?
• Hydrogen
• Oxygen
• Silicon, etc. etc, etc.
• There are over 110 elements
• Only 90 elements are naturally occurring.
• For extra credit list them!
• What is the smallest piece of an element?
• An Atom

3
Abundances of the Elements in the Earth's Crust

• What is the most abundant element in the crust?
• Element Approximate by weight
• Oxygen 46.6
• Silicon 27.7
• Aluminum 8.1
• Iron 5.
• Calcium 3.6
• Sodium 2.8
• Potassium 2.6
• Magnesium 2.1
• All others 1.5

4
Why is oxygen the most abundant?

• We tend to think of oxygen as the gas we breath
  to survive.
• This form of oxygen is O2
• The form found in the earths crust generally can
  be represented like this
• Notice there are 4 O atoms per 1 Si
• Hence the reason for the large amount of oxygen
  in the crust
• The number and kind of atoms as well as the shape
  of the compound determines the nature of matter.

5
Why are there millions of different combinations
of elements all with different natures?

• For instance sodium chloride is a compound made
  of sodium and chlorine atoms in a 1 to 1 ratio.
  It is table salt and essential for life. However,
  if you put pure sodium in your mouth it will
  probably blow your face off! Pure chlorine will
  make you go dead very quickly!
• We will study atoms and how they interact to
  answer this question .
• What is the basic structure of an atom?
• An atom is composed of three primary subatomic
  particles Protons, Neutrons, and Electrons.
• Lets look at an atom of hydrogen and an atom of
  carbon

6
The Hydrogen Atom
What are the components of this atom?
1 proton 1 electron
7
Carbon Atom
How many protons, neutrons, and electrons are in
the carbon atom?
6 Protons 6 Neutrons 6 Electrons
Neither representation is actually how the atoms
look. They are not to scale and weve never seen
a subatomic particle.
8
This is a STM an actual tracing of carbon atoms
in the form of graphite
9
How big are atoms?
This is a mole of carbon atoms 12.0 grams.
One mole is 6.02 x 1023
What if these carbon atoms were eggs? While a
dozen eggs will make a nice omelet, a mole of
eggs will fill all of the oceans on earth more
than 30 million times over. Think about it It
would take 10 billion chickens laying 10 eggs per
day more than 10 billion years to lay a mole of
eggs.
10
More properties of subatomic particles and the
atom
Therefore the atom is mainly empty space!
All the mass of an atom is from the protons and
neutrons. Protons and neutrons are located in the
nucleus. If the nucleus of a typical atom was
the size of a golf ball, and the golf ball was
set on the 50 yard line of Invesco Field, the
outer part of the atom would be just outside the
stadium!
11
The number of protons in an atom determines the
element

• If an atom has 4 protons, what element is it?
• Be
• 79 protons?
• Au

If an atom has 6 protons and 8 neutrons, its mass
is 14 amus. A mole of these atoms would have a
mass of 14 grams.
Another atom with 6 protons and 6 neutrons would
have what mass?
Both of the above atoms are what element?
Carbon
Atoms of the same element with different masses
or different numbers of neutrons are called
ISOTOPES.
12
IONS

• Some Atoms will gain or lose electrons to achieve
  a more stable electronic state.
• An atom that has a charge, not the same number of
  protons and electrons, is called an ion.
• If an atom gains electrons, what charge will the
  atom carry?
• Negative
• It is called an anion.
• If an atom loses electrons the atom will now
  have a positive charge.
• It is called a cation.

13
Combining the atoms

• A combination of two or more atoms that are
  chemically combined is called a compound.
• There are three ways in which atoms combine to
  form compounds.
• Ionic Bonding
• Covalent Bonding
• Metallic Bonding

14
Ionic Bonding

• Ions of opposite charge will be attracted to
  each other, they will form a bond that
  neutralizes the charges.

Ionic bonds generally occur between metals and
non-metals. Compounds formed are usually salts,
NOT molecules.
15
Examples of ionic compounds

• NaCl
• MgCl2
• CaS
• Na2SO4
• SO42- is a polyatomic ion, a group of atoms
  covalently (we will discuss later) bonded acting
  as one ion.

Why are their different subscripts in the
chemical formulas?
16
Writing ionic formulas

• Ions of different charges will be attracted to
  each other. Law of Charges
• This is similar to opposite poles of a magnet
  attracting each other.
• Ions will form bonds so that the NET charge of
  the compound is 0.
• For instance if an ion has a charge of 1 it
  will seek out an anion with a 1- charge.
• Or, two 1 cations will bind with one 2- anion.
• Any combination of cations to anions, as long as
  the charges add up to zero.
• Cations are metals, and are written first in the
  formula.
• Anions are non-metals, are written second, and
  usually have an ide ending.

17
Examples of Ionic Formulas

• Na Cl- ? NaCl
• Mg2 F- ? MgF2
• You do the following
• Cu I- ?
• Fe2 Br- ?
• Pb4 O2- ?
• Al3 S2- ?
• Sc CO32- ?
• NH4 O2- ?
• Sn2 PO43- ?

18
Covalent Bonding

• Some atoms combine by NOT forming ions but by
  sharing electrons to form a more stable state.
• This occurs between non-metals
• These compounds that are formed are called
  molecules.
• Examples CO2, N2, O2, C6H12O6, SiO4
• There are over 1 million natural and man made
  molecules!
• Molecules are named differently than ionic
  compounds. We will not concern ourselves with
  naming or writing formulas for molecules.

19
Metallic Bonding

• This type of bonding occurs between metals.
• It a special situation where many atoms share the
  same electrons.
• Therefore, electrons can move freely from one
  atom to the next.
• That is why metals conduct electricity!

20
Minerals

• A mineral is a naturally occurring compound.
• They can either be ionic, covalent, or metallic.
• We will discuss this at length in our next unit.