Chemical Bonding and the
Periodic Table
There are three types of elements
METALS: have luster, are good conductors of heat and
electricity, typically solid at room temperature and most are
malleable and ductile.
Non Metals: no luster, poor conductors, non malleable,
non ductile, and many are gases at room temperature
Metalloids: share characteristics of both
Remember these areas!
Covalent Bonding
 Elements share electrons in order to fill
valance shells. S and P block elements
follow Octet rule
 Typically occur between non-metals,
metalloids, and a mixture of both
 Hydrogen behaves as a non metal even
though its on the left side of the periodic
table
Lewis Dot Structures
 A Lewis dot structure is like a simplified electron
energy level model.
 The Lewis structure contains the element symbol
with dots representing electrons.
 The only electrons shown are those on the outer
energy level or valence electrons.
 The electrons are placed around the element
symbol, one at a time, clockwise or
counterclockwise, and then grouped in pairs as
more electrons are added.
Covalent Bonds in Lewis dot
diagrams
 Two electrons between atoms form a covalent
bond
 Bonds are drawn as lines and count for two
electrons around that atom
 Extra electrons then pair up around the more
“electronegative” element, the element more to the
right on the periodic table.
 Ideal configurations result in eight electrons
around each atom *hydrogen needs only two
electrons since its part of the K shell
Water: first do the dot diagrams for
each atom
Make Molecule
Extra electrons not in a
bond are called “lone
pairs”
These lone pairs result in
one side of the water
molecule to have a more
negative charge than the
other
This is called a polar
covalent molecule
The Water Molecule
Molecule Instability
 If molecule forms that
has more than two
lone pairs it will react
readily to get rid of the
extra electrons
 Where is the problem
with hydrogen
peroxide-draw in the
lone pairs
Polar vs Non Polar
 Polar molecules have a positive and
negative part
 Will mix with other polar substances, + on
one molecule will be attracted to – on
another molecule
 Non polar molecules share all electrons
equally. No + or – end
 Non polar will not mix with polar because of
lack of electrostatic attraction!
Non Polar Molecules
 Have a symmetric
structure
 Compounds with a
high percentage of
carbon bonded to
hydrogen are non
polar
 Do NOT mix with water
Covalent Compound Characteristics
 Do Not Conduct Electricity
 Low Boiling and Melting Points due to strong
intramolecular forces but weak intermolecular
forces
 Polar compounds will have higher melting/boiling
points than non polar compounds
 Usually liquids or gases
 When solid, will be brittle and good insulators
Ionic Compounds
 Occur between metals and non-metals
 Electron transfer occurs, one substance
loses while another gains electrons
 CATION=Substance that loses electrons
now has more protons than electrons thus
net positive charge
 ANION=Substance that gains electrons and
now has more electrons than protons thus a
net negative charge
Metals form Cations, Non Metals form
Anions, metalloids can be either
Transition Metals can form more
than one possible Cation
Ionic compounds are held together
by electrostatic forces. Opposites
Attract!
Characteristics of Ionic Compounds
 Conduct electricity well when dissolved in
water “electrolytes”. Solids do not conduct
well
 High melting and boiling points due to strong
electrostatic intermolecular forces
 Mostly solids. Solids will have different
shapes depending on cation to anion ratio in
molecule
Different Crystal Structures come
from cation/anion rations
CaF2
Fluorite
Polyatomic Ions
Common Polyatomic Ions
Polyatomic Ions
 Stable covalent molecules (non-metals) that form
with an unbalance of protons and electrons, hence
they are ions
 Have their own chemical and physical properties
like other compounds
 Form electrically neutral ionic compounds with
metals
 When these compounds dissolve, only the metal
and the polyatomic ion as a whole separate, the
polyatomic ion’s atoms stay together
Making Ionic Compounds with
Polyatomic Ions
Combine sodium with the ion hydroxide ‘OH’
Na forms a +1 cation
Hydroxide OH is a -1 anion
Combine to form neutral compound, charge
on cation must be cancelled by charge on
anion
 NaOH
 Try it with Calcium………..




Calcium Hydroxide
 Calcium forms a +2 cation
 Hydroxide is -1 anion so need two of them
for every one calcium
 Ca(OH)2
 Parentheses work just like in math, subscript
goes with whatever is in the parentheses
Compounds with Polyatomic Ions