How do we Draw Atoms?
 Bohr Models

Lewis Dot
Diagrams
1.
How
to draw a Bohr Model
Draw a nucleus & put protons and neutrons inside.

2.
(may use a square shape so you don’t draw any electrons on
it)
Remember the p=e in a neutral atom, so begin putting
electrons on the energy levels until you use them all
up.

Fill energy levels in order (can’t put any in 2nd shell until
you’ve filled the first)
Drawing
Bohr
models,
cont…
Helpful hints:
Draw electrons at each of the four “corners”, then double
up
2. Write the number of electrons you drew (in parentheses)
on each energy level to help you keep track.
1.
Electron configurations (Bohr Models)

But…that can be a pain…
 Most of the time we only really care about the valence
electrons
 Valence Electrons- electrons in the outermost shell
 Also the GROUP NUMBER!!!
Valence Electrons Find the number of valence electrons by
counting over the rows (skipping transition
metals)
 See next slide
Valence Electrons are what react
and bond!
How to draw a Lewis Dot Structure
Find the group # (top of the row on the PT)
2. Write the symbol.
3. Draw dots around the symbol equal to the group
number (if group 2- draw two dots)
1.
1.
Place dots one at a time around the top, right, bottom
and left side of the atom before you double any up.
How to draw a Lewis Dot Structure
1. Find the group # (top of the row on the PT) Let’s
do Phosphorus
2. Write the symbol. P
3. Draw dots around the symbol equal to the group
number (if group 2- draw two dots)
1.
Place dots one at a time (clockwise) around the top,
right, bottom and left side of the atom before you
double any up.
Octet Rule Most atoms want to have 8 electrons in their outer
shell.
Octet
rule exceptions…
 (octet rule=Most
atoms want to have 8 electrons in
their outer shell)
 Helium What is its group number?
 Why doesn’t it make sense to draw that many dots?
 Because it is easier for it to fill that first shell which only
needs two electrons
 Other- Exceptions:

___H__ , __Li___ , __Be___
Elements with a full outer shell
naturally (Noble Gases)
Lewis Dot Structures
Atomic Mass Mystery…
 Look at the average atomic mass for Oxygen. What
does it say (exactly?)
 15.9999
 What is the mass number?
 P + N = whole number
 So what the heck!?!?!
 Average of the actual isotopes’ mass numbers and
abundance on Earth!!!
How can we change the mass of an
element?
 We can’t mess with protons, but what CAN we “mess
with?”
 Neutrons…



What would that change about the atom?
Changes the MASS
Get an ISOTOPE
Isotopes
 Isotopes are different atoms of the same element that
contain the same number of protons but different
number of neutrons.
 Examples

Cl-35
vs.
Cl-37
17P
17P
18N
20N
How to write isotopes…
 Mass/Hyphen Notation:
 Especially important for a form of the isotope that is
NOT the “usual”
 Write the symbol, a dash, and the mass # for that
isotope
 Ex’s


C-14
C-12
How to write isotopes…
 Nuclear Symbol Notation
 Includes the symbol, atomic #, and the mass # for that
isotope
 Ex’s
14
6
Mass #
Atomic # (=p)
C
What else CAN we “mess with?”
 Already know…Neutrons…
 Get an ISOTOPE, changes the mass
 But what if I mess with Electrons…
 What would that change about the atom?
 Changes the CHARGE
 Get an ION
How
are
these
ions
made?
 Can you mess with protons?
 Would messing with neutrons do
anything to the charge?
 What must you mess with???
 What charge does an electron
have?
 So what would happen to the atom
if they LOSE one? Would they get
more positive or more negative
overall???
IONS
 If you mess with the electrons you change the overall
charge of the atom…an atom that is no longer neutral
is called an ION.
 Anion- has a negative charge
 Means you added an electron!
 Cation- has a positive charge
 Means you lost an electron