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• Valence Electrons are the electrons in
the highest occupied energy level of an
• The number of valence electrons
determines the chemical properties of
• To find the number of valence electrons
in an atom of a representative element,
look at the group number. (see table
• Valence electrons are usually the only
electrons used in chemical bonds, so they
are show in electron dot structures.
• In forming compounds, atoms tend to
achieve the electron configuration of a noble
• This is called the Octet Rule.
• All atoms want to have 8 electrons in their
outer or valence shell.
Formation of Cations
• Atoms of the metallic elements tend to lose
their valence shell electrons leaving 8 in the
next level down.
• An atom’s loss of valence of electrons
produces a cation, or positively charged ion.
• Remember, an ion is a charged atom that
has lost or gained electrons during the
chemical bonding process.
Now I’m bigger
• For transition metals, the charges of
cations may vary.
• For example, elements such as
iron, nickel and copper may lose 1
to three electrons depending on the
Formation of Anions
• A anion is an atom or group of atoms with a
• The gain of a negatively charged electron by
a neutral atom will create an anion.
• Non-metals typically form anions.
• The name of the anion is not the same as
the name of the atom.
• It usually ends in –ide. (See table 7.2)
• Valence electron
• Octet Rule
• Transition Metal
SUM IT UP
• An electron configuration is a way to
show the electrons in a particular
atom in the proper order.
• Since electrons are arranged in
shells, each shell has a different
• Use the periodic table to figure out
the electron configuration for any
POST IT UP
What is the electron
configuration for carbon?
7.2 Ionic Bonds and Ionic
• Compounds composed of cations and
anions are called ionic compounds.
• Ionic compounds are usually composed of a
a metal and other nonmetals.
• Although they are composed of ions, they
are electrically neutral…meaning no charges
or their charges cancel out.
• Bonds that hold ionic compounds together
are called ionic bonds.
• A chemical formula shows the kinds and
numbers of atoms in the smallest
representative unit of a substance.
• A formula unit is the lowest wholenumber ratio of ions in an ionic
• The chemical formula is not always the
lowest whole number ratio.
• How many kinds of atoms are in each of
these ionic compounds?
Properties of Ionic Compounds
• Most ionic compounds are
crystalline solids at room
• Ionic compounds generally have
high melting points.
• Ionic compounds can conduct an
electric current when melted or
dissolved in water.
SUM IT UP
How many kinds of
each of these atoms
are in this
8.1 Molecular Compounds.
• Some compounds are not ionic.
• Instead of giving or taking electrons, these
compounds share electrons to complete their
• This is called a covalent bond.
• A molecule is a neutral groups of atoms
joined by a covalent bond.
• A diatomic molecule is a molecule consisting
of only two atoms.
• A compound composed of molecules is
called a molecular compound.
• A molecular formula is the chemical
formula of a molecular compound.
• It shows how many of each element
a molecule contains.
• A molecular formula does not tell
you about a molecule’s structure.
8.2 The Nature of Covalent
• In forming covalent bonds, electron
sharing usually occurs so that atoms
attain the electron configuration of a
• Combinations of nonmetallic elements
in groups 4A, 5A, 6A and 7A are likely
to form covalent bonds.
• They share electrons to achieve an
octet like a noble gas.
• An electron dot diagram represents the
shared pairs of electrons in a molecule.
• Each bond is two electrons or two dots.
• A structural formula represents the covalent
bonds by dashes and shows the
arrangement of the atoms.
• Each dash will equal two electrons.
• A pair of valence electrons not shared
between atoms is called an unshared pair,
lone pair or nonbonding pair.
• A polyatomic ion is a tightly bound
group of atoms that has a positive
or negative charge and behaves like
• A group of atoms may be covalently
bonded as a polyatomic ion but
since the whole unit has a charge, it
can bond with other charged ions.
• Covalent bond
• Polyatomic ion
• Unshared pair
SUM IT UP
8.4 Polar Bonds and Molecules
• Covalent bonds involve sharing between atoms.
• However, some atoms are more electronegative
than others meaning they tend to attract more
electrons than other atoms.
• When all the electrons are shared equally, it is a
nonpolar covalent bond.
• When one atom attracts electrons more strongely
than the other atom, a polar covalent bond forms.
• The atom that attracts more electrons become
slightly negative while the other becomes slightly
• This is NOT the same as an ionic bond with normal
• Hydrogen bonds occur when a hydrogen that
is covalently bonded to another atom will be
weakly attracted to another atom on another
• The partial positive charge of the hydrogen in
the polar molecule, gets attracted to the
partially negative charge on another
• Water usually forms hydrogen bonds.
• As a result, life is possible.
• Polar molecule
• Hydrogen bond
POST IT UP
Why is water polar?
Create an accurate model for a chemical
compound. Label the atoms and the bonds.
Bigger models with more atoms get more