Valence Electrons
&
Bohr Diagrams
Atomic Structure
• Atoms have a nucleus that contains
Protons and Neutrons
• Electrons are contained in shells that
surround the nucleus
• An atom is made of mostly empty space
• Protons have a positive charge
• Electrons have a negative charge
• Neutrons are Neutral
Valence Electrons
• Each electron shell can
hold a certain number of
electrons
• Electron shells are filled
from the inside out
• Noble Gases have full
outer electron shells
• All other elements have
partially filled outer
electron shells
Electron
Shell
1
Number of
Electrons
2
2
8
3
8
4
18
5
18
6
32
7
32
Valence Electrons
• The electrons in the outer most electron
shell are called valence electrons
• The shell containing electrons that is
furthest from the nucleus is called the
valence shell
• The number of electron shells with
electrons is the same as the period
number
Noble Gas Stability
• Noble gases are usually unreactive
• This is because they have full valence
shells
• An element with a full valence shell is a
happy element 
• For two atoms to join together atoms must
gain, lose or share electrons
• Elements with full valence shells do not
easily gain or lose electrons
Noble Gas Stability
• Atoms want to gain stability
• Atoms will try to gain or lose electrons to
have a full valence shell
• Metals try to lose electrons
• Non-Metals try to gain electrons
Becoming An Ion
• Electrons are negatively charged
• Protons are positively charged
• Neutral atoms do not have a charge
because the number of protons is the
same as the number of electrons
• When atoms gain or lose electrons they
become positively or negatively charged
• An atom with a charge is called an Ion
The Octet Rule
• To draw the electron configuration of a neutral atom, look
at the ATOMIC NUMBER.
• Neutral atoms have the same number of electrons and
protons
• The first shell only holds 2 electrons
• Every other shell is filled up to 8 electrons
• The “left over” electrons are found on the last shell. The
last shell is the valence shell and these electrons are
called valence electrons.
• Valence electrons tell us which atoms will likely combine
with others in order to ‘share’ 8 electrons on their last
shell. All matter wants to be stable.
ATOMIC MASS
• The atomic mass tells us how heavy an
atom is. The mass is calculated by the
total protons and neutrons in the nucleus
of an atom.
• Electrons are so tiny their mass is not
counted in the overall mass of an atom.
Their mass is considered negligible.