### Lewis Dot Diagrams

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
1. It helps to have identified the number of
protons, neutrons & electrons an atom has
before you try to draw it. You can find this by
using this by using isotope notation
2. Isotope notation (shown below for uranium
238) uses information from the Periodic Table
to determine the number of protons,
neutrons & electrons in an element.
1.
2.
3.
The info. on the
Periodic Table is
rearranged to
allow for easy
calculation
The mass goes at
the top left corner
of the element’s
atomic symbol
The number goes
at the bottom left
corner.
4. The atomic number
is equal to the number
of protons &
electrons, too.
5. The number of
neutrons is equal the
mass minus the
number
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
Using Uranium 238 as our example, the
number of both protons and electrons is
equal to 92, which is the atomic number.
The number of neutrons is equal to 238-92
or 146, which is the atomic mass minus the
atomic number.
146

Bohr diagrams show all the protons &
neutrons found in the nucleus, and all the
electrons in all the energy levels of the
electron shell.

A simplified Bohr diagram uses the chemical
symbol of the element in the center, instead
of showing all the protons & neutrons. It still
shows all the atoms in all the occupied shells.
Li




Lewis dot diagrams show only the outermost
(valence) electrons.
Valence electrons are only found in the outermost
shell of an atom.
The periodic table helps you to predict how many
valence electrons an element will have.
Shells fill up in this order:
Shell
1st
2nd
3rd
etc.
# of electrons it holds
2
8
18


So examples of dot diagrams look like this:
Lewis dot diagrams can also show how
chemical bonds form between atoms:
electrons from
electrons from
hydrogen are
yellow
oxygen are red


If you remember that it takes two electrons to
make a chemical bond, then molecules can
also be shown as:
Double bonds can be shown, too
double bond

Forming ionic bonds can be represented as:
..
to give Na+ :Cl:..

Forming covalent bonds can be shown as
```