Ionic and molecular compounds
 Ion: is an atom or a group of atoms that has an electric
charge.
 When a neutral atom transfers one or more electrons to
another atom , it results in the formation of an ionic
compound.
 Example: You and your friend go to a market that sells
apples for 40 cents each and oranges for 50 cents each. You
have 45 cents in your pocket and want to buy an apple. Your
friend also has 45 cents in his pocket but wants to buy an
orange. If you give your friend 5 cents he can buy an orange
and you can still buy an apple. Transferring the nickel to
your friend gets both of you what you want. In a simple way
your actions model what can happen between atoms.
 An atom that loses a valence electron becomes a positive ion.
 When an atom gains an electron it gains a negative charge and
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becomes a negative ion.
Example: If an atom loses two electrons what charge will the ion
have? Positive two (+2). If an atom gains three electrons what
charge will the ion have? Negative three (- 3).
Positive ions are also called cations.
Negative ions are also called anions( when dealing with
electricity).
An ionic compound is made up of positive and negative
compounds.
How does an ionic compound form? The transfer of electrons
from one element to another.
 Page 365 figure 1
 Two elements ,potassium(K) and Fluorine (F)
 Answer the following questions:
 Which atom is about to lose an electron?
 Which atom is in the cartoon?
 What happens to the atom when it loses the electron
 What happens to the fluorine atom?
 Some ions are made of several atoms.
 Ions that are made of more than 1 atom are called
polyatomic ions.
 Atoms that easily lose electrons react with atoms that
easily gain electrons, thus valence electrons are
transferred from one type of atom to
another.(example: sodium and chlorine atoms reacting
to form sodium chloride, known as table salt).
 Positive and negative charges attract each other.
 How does this affect positive and negative ions? They will
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be attracted to each other.
When an atom loses an electron, where does the electron
go? To an atom that tends to gain electrons.
Oppositely charged particles attract and form an ionic
bond.
When oppositely charged ions bond the result is an ionic
compound.
An ionic compound is made up of positive and negative
ions but the overall charge on the compound is zero.
Example: The positive Na ion and the negative CL form the
ionic compound NaCL which has no charge.
Naming ionic compounds
 Formulas for Ionic compounds:
 A chemical formula is a group of symbols that shows the
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ratios of elements in a compound.
Subscripts tell the ratio of elements in a compound.
Example: CaCL2-the ratio of calcium ions to chloride ions
is 1 to 2.
Rules for writing a formula for an ionic compound: The
name of positive ion comes first, followed by the name of
the negative ion.
If the negative ion is a single element the end of the name
changes to –ide. Example CaO is called calcium oxide.
If the negative ion is polyatomic its name usually ends in –
ate or – ite .Example NH1NO3 called ammonium nitrate.
How do molecular compounds
form?
 The chemical bond formed when two atoms share
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electrons is called a covalent bond.
Covalent bonds usually form between nonmetal atoms
What are two covalently bonded atoms called? A molecule
A molecular compound is a compound that is made up of
molecules.
Example: you and your friend want to buy a sandwich that
sells for 1 dollar. Each one of you has only 50 cents. If you
combine your money you can buy the sandwich and share
it. Similarly 2 atoms can form a bond by sharing electronsthus covalent bond
 Atoms in some covalent compounds tend to have slight electrical
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charges.
Atoms of some elements pull more strongly than atoms of other
elements .As a result electrons are shared unequally.Unequal electron
sharing causes electric charges.
Example :tug of war.Two groups pulling a rope.Rope moves towards the
stronger team.Same concept with electric charges in covalent bonds.
If 2 atoms pull equally on the electrons neither atom becomes
charged.This is called a nonpolar bond-a covalent bond in which
electrons are shared equally.
A covalent bond in which electrons are shared unequally is a polar
bond.
The atom with the stronger pull gains a negative charge.
The atom with the weaker pull gains a positive charge.
 Polar bonds form when the atoms of a molecule
unequally share the electrons.
 Not all polar bonds result in polar molecules(positively
and negatively charged).
 Example : CL2 is a not a polar molecule. Molecular
chlorine has a non polar bond. Molecules that are
made up of two identical atoms show equal sharing of
electrons, thus a nonpolar molecule..
What determines properties of
metals
 Each property of metals is determined by the structure
of metal atoms and the bonding between their valence
electrons.
 Properties: shiny, bendable, can conduct heat and
electricity
 How does a metal’s high thermal conductivity relate to
its valence electrons? The loosely attracted electrons
move and transfer heat from electron to electron.
 Why do metals have high luster? The valence electrons
absorb light and then re emit it which gives a shiny
look.