Atomic Theory

1
Atomic Theory

• Atom
• smallest part of an element with that elements
  properties
• 2 parts
• Nucleus
• Protons (positive charge, weigh 1 amu)
• Neutrons (neutral charge, weigh 1 amu)
• Orbitals (inside electron cloud)
• Electrons (negative charge, negligible mass)
• ( amu atomic mass unit)

2
A note about electrons

• They dont all have the same amount of energy.
• The farther away from the nucleus they are, the
  more energy they have.
• We dont know exactly where they are, we just
  have an idea. They move fast, like the blades of
  a fan. We know theyre there somewhere.
• Outermost ones are called valence electrons.
  They are responsible for how elements react
  with each other and the physical and chemical
  properties.

3
Electrons

• Electron cloud is split into energy levels that
  hold different amounts of electrons.
• 1st one holds 2 (maximum)
• 2nd one holds 8
• 3rd one holds 18
• 4th one holds 32
• Electrons fill the lowest one first
• The energy levels are split into orbitals, called
  s, p, d and f.

4
So it gets complicated

• Really the 8 electrons in the second energy
  level are 2 in the s orbital and 6 in the p
  orbital
• And the 18 in the third energy level are 2 in
  s, 6 in p and 10 in d orbital

5
s, p, d, f orbitals

• You can see this pattern on the table!

6
Do we have to know this?

• But youll hear more about that in chemistry.
  For now realize that each energy level is made
  up of sublevels that hold specific amounts of
  electrons.
• The sublevels are called orbitals and are named
  s, p, d, f
• You can see these patterns in the periodic table.

7
The Periodic Table

• Was organized according to the chemical
  physical properties of the known elements
• Protons, neutrons and electrons had not yet been
  discovered
• Dmitri Mendeleev noticed that when the elements
  were put into order by their atomic mass, some
  of their properties repeated periodically (at
  regular intervals)
• This is because the pattern of valence electrons
  repeats as orbitals are filled

8
What it tells you

• Atomic number
  the number of
  protons
• Atomic mass
  average mass for all the forms of that
  element
• Name of the element
• Symbol (first letter always capital)

9
Ions

• Atoms arent always neutral (no charge)
• Lose electrons
• More protons, positive ion
• Gain electrons
• More electrons, negative ion
• Has 1 charge for each electron lost or gained
• Written above the symbol, e.g. Na, O2-

10
Isotopes

• Some forms of the atom naturally have more or
  less neutrons
• Because it has the same number of protons its
  still the same atom, but called an isotope.
• Thats why atomic mass is not a whole number, it
  averages all the isotopes
• Write the mass number and atomic number to left
  of symbol
• C is carbon-14, used to carbon date

14
6
11
Patterns on the table

• Rows are called periods
• As you go across a period
• Atomic number (p) increases by 1
• So does e- for neutral atoms
• So does valence electrons
• Columns are called families or groups
• Similar properties (density, melt pt, etc.)
• React chemically the same way
• Because have same valence electrons

12
How you use it

• p to Atomic Number (by definition)
• e- protons (in a neutral atom)
• n0 atomic mass, rounded off atomic number

13
Bohr Model

• Shows protons and neutrons in nucleus
• Shows electrons in the cloud in layers called
  energy levels

14
Lewis Diagram

• Also called dot diagrams
• Only shows valence electrons (outer most)
• Valence are only ones involved in chemical
  reactions