Introduction to Chemistry
Bohr 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
Electrons
Symbol
Name
Atomic Mass= Number of Protons + Number of
Neutrons
I
+1
II
III IV V
+3 +/-4 -3
+2
= element charges
= Valence Electrons
VI
-2
VIII
VII 0
-1
Periods and Groups
• Periods go from left to • Groups go up and down
right
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 Diagrams
Try the following
elements on your own:
a)
b)
c)
d)
e)
f)
H
He
O
Al
Ne
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)
b)
c)
d)
e)
f)
H
He
O
Al
Ne
K