Introduction to ChemistryBohr Models and Lewis Dot Structures

Atoms• Basic unit of matter• Consists of: Electrons, Protons, & Neutrons

Atoms Review• Consists of: Electrons, Protons, & Neutrons– Electrons: particles orbiting around nucleus

with a negative charge– Protons: particles in the nucleus with positive

charge– Neutrons: particles in the nucleus with no

charge

Element• a pure chemical substance consisting of one type of atom

Atomic Number= Number of Protons or ElectronsSymbolNameAtomic Mass= Number of Protons + Number of Neutrons

+1

+2 +3 +/-4 -3 -2 -1

0

Periodic Table of Elements

= element charges = Valence Electrons

I

II III IV V VI VII

VIII

Periods and Groups

• Periods go from left to right

• Groups go up and down

Bohr Models

• Proposed by Niels Bohr in 1915• Electrons orbit the nucleus in orbits that

have a set size and energy. • The energy of the orbit is related to its size. • The lowest energy is found in the smallest

orbit.

Energy Levels• When two atoms approach each other their

nucleus do not touch• Only electrons are involved in Chemical

Reactions

Bohr Diagrams • Find out which period (row) your element is in.

• Elements in the 1st period have one energy level.

• Elements in the 2nd period have two energy levels, and so on.

Bohr Models RULE• Show just electrons with energy levels• 1st level holds 2• 2nd holds 8• 3rd holds 18 but is stable at 8• 2-8-8 RULE!!• Must fill an energy level to capacity before moving

to the next energy level

Bohr DiagramsTry the following elements on your own:

a) Hb) Hec) Od) Ale) Nef) K

P:N:

Valence Electrons• Electrons that are found on the outer most

energy level. This determines the elements chemical properties

Lewis Dot Structures• Named after Gilbert Newton Lewis• Show the bonding between atoms of a

molecule, and the lone pairs of electrons that may exist in the molecule

• Show only valence electrons (outer energy level)

Lewis Dot Structures and Groups• Find out which group

(columns) your element is in.

• Elements in the 1st group have one valence electron.

• Elements in the 2nd group have two valence electrons, and so on.

Lewis Dot

Try the following elements on your own:

a) Hb) Hec) Od) Ale) Nef) K

MORE PRACTICE

ANSWERS