The Bohr Model
&
The Lewis Structure
Remember Bohr?
• Niels Bohr ( 1885 - 1962 ) – a Danish
scientist
• Studied at Cambridge
• Worked in the Professor Rutherford’s
lab
• Published 115 times
• Escaped the Nazi’s when they
occupied Denmark
• Won Nobel Prize in Physics in 1922
• Explained that colors make up a line
spectrum
The Bohr Model
• First, there are some errors in the Bohr Model
• The model is simpler and relatively easy to
understand
• Shows that the electrons in atoms are in orbits of
differing energy around the nucleus
• Uses the term energy levels (or shells) to
describe the orbits of differing energy
• The higher the energy-level number, the farther
away the electron is from the nucleus – the
higher the energy
The Shell Count…
Shell Number
1
2
3
4
Maximum # of
Electrons
2
8
18
32
Let’s Make a Bohr Model
Take the element Nitrogen
N
The symbol is?
The Atomic Number is?
Which means the number of Protons and Electrons are?
7
Draw a circle for the
Nucleus and identify
how many protons
7P
Draw a circle to
represent the first
shell and place max
of two electrons
7P
Draw a
circle to
represent
the second
shell and
place a max
of eight
electrons
7P
7
Let’s Make a Bohr Model
Take the element Neon
The symbol is? Ne
The Atomic Number is?
Which means the number of Protons and Electrons are?
10
10P
10P
10P
10
Let’s Bring it All Together!
Tell me what group Oxygen is in?
6
Tell me what period Oxygen is in?
2
How many protons does Oxygen have? 8
8P
8P
8P
Do you see the trick?
Tell me what group Oxygen is in?
Tell me what period Oxygen is in?
6
2
How many protons does Oxygen have?
What period? Does it
match the number of
shells?
8
8P
What group? Does it
match the number
electrons in the outer
shell?
Now you try…
Take the element Carbon and draw the Bohr Model.
Now check yourself… what period is Carbon? what
group is Carbon? Do they match the number of
shells and the number of electrons in the outer
shell ?
Now you try…
Take the element Calcium and draw the Bohr Model.
Now check yourself… what period is Calcium? what
group is Calcium? Do they match the number of
shells and the number of electrons in the outer
shell ?
Who is Gilbert Lewis?
• Gilbert Newton Lewis (1875 – 1946)
• Died in his laboratory in the University of
California Berkeley at age 70
• Introduced the Lewis Dot Structure
• Postulated the electron pair relationship of
acids and bases known as the Lewis Theory
• Set the standard for Chemical Thermodynamics
• First to produce deuterium and isolated
naturally occurring heavy water
What is the Lewis Dot Structure?
• It depicts paired and unpaired valence electrons
(those electrons in the outer shell)
• Also called the electron-dot diagrams
• Represents the covalent bonding of a molecule (or
ion)
• Covalent bonds are chemical bonding formed by the
sharing of electrons in the outer most shell
• The atoms in a Lewis Structure tend to share
electrons so that each atom has eight electrons (the
octet rule – that states an atom in a molecule will be
stable or “happy” when there are eight electrons in the
outer shell)
• Lewis Structure displays the electrons of shells
because these are the ones that participate in making
chemical bonds
Lewis Structures
1) Write the element
symbol.
2) Carbon is in the 4th
group, so it has 4
valence electrons.
3) Starting at the right,
draw 4 electrons, or
dots, counterclockwise around the
element symbol.
Lewis Structures
1) Check your work.
2) Using your periodic
table, check that
Carbon is in the 4th
group.
3) You should have 4
total electrons, or
dots, drawn in for
Carbon.
Now try yourself…
1)
2)
3)
4)
5)
6)
7)
8)
K
Mg
Al
Si
P
S
Cl
Ne