Ion: a single charged atom or a small
group of atoms with a charge.
negative charge (anion)
positive charge (cation)
Element
Symbol
cesium
barium
arsenic
iodine
Zinc
Phosphorous
sulfur
Electron
configuration
Electron
dot
structure
Electrons
lost or
gained?
Ion
symbol
Ion name
Element
Symbol
Electron
configuration
Electron
dot
structure
Electrons
lost or
gained?
Ion
symbol
Ion name
Cs
[Xe]6s1
Cs.
1 lost
Cs+
cesium
cesium
barium
arsenic
iodine
Zinc
Phosphorous
sulfur
Ionic Compounds
1. Ionic compounds are formed between
oppositely charged ions, usually a metal and
one or more non-metals because they have a
large difference in their electronegativity.
2. Binary ionic compounds are
composed of two single
atom ions.
Naming
Binary ionic compounds are named by removing
the end of the name from the nonmetal and
adding -ide.
Examples:
Sodium & chlorine form Sodium Chloride.
Magnesium & oxygen form Magnesium Oxide.
Calcium & sulfur form Calcium Sulfide.
Writing Formulas for ionic compounds
1. Find charges on each ion.
(Look on the periodic table or ion table.)
2. The positive and negative charges must exactly
balance each other in order to form a neutral
compound.
Ex:
Sodium forms a +1 charged ion:
Sulfur forms a -2 charged ion:
Na+1
S-2
The formula for Sodium Sulfide is:
Na2S
Calcium
Fluoride =
Potassium
Chloride =
Lithium
Oxide =
Aluminum
Sulfide =
Calcium
Potassium
Fluoride = CaF2 Chloride = KCl
Lithium
Oxide =
LiO
Aluminum
Sulfide =
Al2S3
Polyatomic Ionic Compounds
Sometimes a group of atoms can have a charge. This is
called a polyatomic ion.
Some common poly atomic ions are:
nitrate NO3-1
sulfate SO4-2
carbonate CO3-2 bicarbonate (or hydrogen carbonate)
hydroxide OH-1
HCO3-1
Notice that the names of most of these ions end in -ate.
When you see a name ending in -ate it probably implies
that it is a polyatomic ionic compound.
The groups of atoms can be thought of as a single
entity with a charge, just like a single atom can
have a charge.
Example: Sodium Nitrate needs one +1 sodium ion to
neutralize one -1 nitrate ion, so the formula is
NaNO3
If you need more than one polyatomic ion, then
you put parenthesis around it in the formula.
Example: Calcium Nitrate needs one +2 calcium ion to
neutralize two -1 nitrate ions, so the formula is
Ca(NO3)2
Sodium Sulfate =
Zinc Phosphate =
Barium Hydroxide =
Ammonium Sulfate =
Sodium Sulfate =
Zinc Phosphate =
Na2SO4
Zn3(PO4)2
Barium Hydroxide =
Ammonium Sulfate =
Ba(OH)2
(NH4)2(SO4)
Ions with multiple charges
Some atoms (typically transition elements) can
commonly form 2 or 3 different charges.
Copper, for example, usually forms +1 or +2
charged ions.
We specify the ions by adding a Roman numeral to
the name:
Cu+1 is Copper(I) and Cu+2 is Copper(II).
So. . . .
Copper(II)Oxide is CuO
and
Copper(I)Oxide is Cu2O.
Properties of ionic compounds:
1
2
3
o
High melting points (> than 150 C).
Ionic solids conduct electricity when
melted or dissolved in water.
Ionic solids are hard and brittle.
Ionic solids have . . . .
. . . HIGH melting points because ionic bonds
are very strong. Electrostatic forces hold
positive cations and negative anions together
in a strong crystal lattice arrangement.
Ionic solids are . . . .
. . . POOR conductors because electrical and
heat conductivity depends on electrons being
able to move freely.
Electric charge is "locked" in the lattice
positions of the ions in ionic solids.
This means there is poor mobility of charges
and poor conductivity of electricity and heat.
BUT. . . . .
.
Ionic solids are . . . .
. . . good conductors when melted.
When ionic solids
melt, ions are mobile
and can carry
electrical charge
through the liquid.
This is why a molten
ionic substance
conducts electricity,
but a solid ionic
substance doesn't.
Ionic solids are . . . .
. . . good conductors when dissolved in water. .
The solvent pulls the ions
out of the solid and breaks
the forces holding the
crystal together. The solvent
isolates the ions in an
envelope of solvent
particles. The ions are free
to move and carry electric
charge through the solution.
Ionic solids are . . . .
. . . brittle and hard because the electrostatic
attractions in the solid hold the ions in definite positions.
The attractions must be overcome to move the ions.
When the ions in the solid are shifted by some very
strong force, the positions of ions shift so that like
charged ions are close together. This results in strong
repulsions and the like charged ions move apart. This
causes the solid to shatter and not simply deform like a
metal.