Valence Electrons
Activity
• Fold your periodic table so that the f and d blocks are looped.
• Determine the number of valence electrons for each remaining group
(column).
• Find the pattern.
Valence Electrons
• Valence electrons – Electrons in an atom’s highestnumbered energy level.
• e- config. for Si: 1s2 2s2 2p6 3s2 3p2
• Si has four valence electrons.
• 3s2 + 3p2 = 4 e-
• e- config. for C: 1s2 2s2 2p2
• C also has four valence electrons.
Valence Electrons
• How many valence electrons does selenium have (element
34)?
• e- config: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
• Se has 6 valence electrons.
Valence Electrons Shortcut
• You can tell how many valence electrons
any atom should have by its position in the
periodic table.
1
2
34 5 67
variable
8
2
Why are the valence
electrons responsible
for bonding?
How many valence electrons are in each of
the following elements:
Na (sodium)
Mg (Magnesium)
Xe (Xenon)
Br (Bromine)
C (Carbon)
F (Fluorine)
O (Oxygen)
K (Potassium)
Draw a picture to explain why the valence electrons are
responsible for bonding between different elements.
Try to use the s & p orbital shapes.
Octet Rule
How many valence electrons do each of the
following elements want to lose or gain?
Na (sodium)
Mg (Magnesium)
Xe (Xenon)
Br (Bromine)
C (Carbon)
F (Fluorine)
O (Oxygen)
K (Potassium)
Now, estimate the reactivity of each of the
following elements based on the valence
electrons.
Na (sodium)
Mg (Magnesium)
Xe (Xenon)
Br (Bromine)
C (Carbon)
F (Fluorine)
O (Oxygen)
K (Potassium)
Lewis Dot
Diagrams
Lewis Dot Diagrams
• Electron Dot Diagram – shows the valence electrons of an
atom as dots.
• Distribute dots around atomic symbol to represent valence
electrons.
• Should never have more than 8 dots.
Lewis Dot Diagrams
• Here are the Lewis diagrams for 8 elements,
which have 1 – 8 valence electrons.
Li
Be
B
C
N
O
F
Ne
Draw the Lewis Dot structure for each of the
following elements:
Na (sodium)
Mg (Magnesium)
Xe (Xenon)
Br (Bromine)
C (Carbon)
F (Fluorine)
O (Oxygen)
K (Potassium)
Periodic Trends
Trends
• Atomic radius
• Electronegativity
• Ionization Energy
• How are all these important for bonding to form molecules?
Atomic Radius
Effect of # of protons.
Effect of # of electrons.
• High
Electronegativity =
Strongly seeks to
take an electron
• Low
Electronegativity =
Readily gives an
electron
• High Electronegativity = Strongly seeks to take an electron
• Low Electronegativity = Readily gives an electron
• High Electronegativity = Strongly seeks to take an electron
• Low Electronegativity = Readily gives an electron
• Energy required
for another
atom to remove
an electron.
• ?????
Trends
• Atomic radius
• How is it measured
• Electronegativity
• Ionization Energy
• Melting Point
• Boiling Point
• Conductivity
• How are all these important for bonding to form molecules?
Predict which
elements will react
with other elements.