6-1 IONIC BONDING
Elements’ properties are determined by their
electron configurations.
STABLE ELECTRON CONFIGURATIONS
When the highest energy level of an atom is filled, it
is stable. All of the noble gases have filled outer
energy levels thereby making them inert. An
electron dot diagram is a model of an atom showing
just its valence electrons. The symbol of the atom is
in the centered surrounded by each valence
electron. The symbol represents the nucleus of an
atom.
IONIC BONDS
Ionic bonds form when elements that have
incomplete higher energy levels react until they are
filled. Atoms will gain or loose electrons to achieve
complete energy levels. When an atom gains or
loses electrons, it is no longer neutral and has a
charge. Ions are formed. Ions are represented with
the symbol of the element with a superscript + or –
sign and a number representing the number of
electrons gained or lost. Cations are formed from
atoms that have lost an electron and are now
positive. Anions are ions that were formed from
atoms that have gained electrons and now have a
negative charge.
106739450
1
*Because opposite charges attract, these ions join
together to form a chemical bond. If electrons have
been gained or lost forming ions in a chemical
reaction, then an ionic bond has formed.
*Ionization energy is the amounts of energy needed
to remove an electron from an atom. The trend on
the periodic table is that ionization increases from
bottom to top and from left to right. Because it is
easier to removed electron at the bottom of a group,
the bottom of the groups are more reactive.
*When compounds contain ionic bonds, they are
called ionic compounds. They are represented with
chemical formulas, which is a notation way to write
the reaction and show the ratio of atoms or ions in
the compound. See page 161.
Chemical formulas do not indicate the shape of the
compound. Crystals have a lattice structure that has
a uniform pattern that is repeated.
PROPERTIES OF IONIC COMPOUNDS
Most ionic compounds have a high melting point,
when melted it is a good conductor of electricity, and
it will shatter. The strong bonds formed during ionic
reactions can explain these properties. As a rule of
thumb, a metal and a nonmetal form an ionic bond.
106739450
2
6.2 COVALENT BONDING
As a rule of thumb, two nonmetals will form a
covalent bond. A covalent bond is one in which
electrons are shared between two or more
elements. Figure 9 on page 166 has four
different ways to illustrate a bond between two
nonmetals. When atoms are joined by a
covalent bond, a molecule is formed. Where as
ionic bonds are held together by the electrical
attraction of ions, covalent bonds are held
together by the attractions between the shared
electrons and the protons in each nucleus.
*Chemical formulas are used to describe a
chemical bond. When two atoms of the same
element bond together, they are diatomic. Their
formula would be the symbol of the element with
a subscript of 2.
Example: H2
When atoms form one bond between atoms it is
a single bond. When it forms two bonds
between atoms, it is a double bond, and when it
is three bonds between atoms, it is a triple bond.
106739450
3
The attraction of electrons is greatest at the top
and right in the periodic table. Fluorine has the
greatest attraction of all the elements.
*When the atoms that have a covalent bond have
the same attraction for electrons, the electrons
spend about the same amount of time with each
element. However, when there is a large
difference in electron attraction, the electrons will
spend more time with the element that possesses
the greatest amount of attraction. This creates a
polar bond. This means that there is an unequal
distribution of charges. These bonds are called
polar covalent bonds.
*It’s easy to identify a polar covalent bond but
not so easy to identify a polar or nonpolar
molecule. A polar molecule is polar because of
the covalent bonds AND because of its shape.
If a molecule is nonpolar or if a compound has
ionic bonds, there is very LITTLE attraction
among the molecules. However, if it is a polar
molecule, the molecules tend to be attracted to
each other making it require more energy to
separate them. This results in a higher boiling
point.
106739450
4
6.3 NAMING COMPOUNDS AND WRITING FORMULAS
Scientists needed a system for naming
compounds that could be universally
understood and reflects the composition of the
compounds. There are basically two systems
of naming and their bonding differentiates
them.
NAMING IONIC COMPOUNDS
The name of an ionic compound tells what
elements are combined. The formula gives
the ratio. A compound that has only two
elements is a binary compound. The cation
name is always first and the anion is always
second in a binary compound. The cation
name is unchanged while the anion uses the
root name of the element with the “ide” suffix
added to it. Iodine becomes iodide and sulfur
becomes sulfide. Many of the transition
metals can have more than charge.
Therefore, when naming an ionic compound
that contains a transition metal, a roman
numeral follows the cation and it is equal to
the charge. For example copper (II) oxide
106739450
5
would tell you that copper has a positive two
charge.
POLYATOMIC IONS
Polyatomic ions are a group of atoms that are
covalently bonded together and have a
positive or negative charge and act as a unit.
Examples are on page 173. When naming
compounds that have polyatomic ions, do not
change the name of it.
WRITING FORMULAS
If you know the name of the ions, you can
write the formulas. Write the cation first and
the anion last. Use subscripts to show the
ratio of the ions to each other. Remember that
formulas are neutral so there must equal
number of positive and negative charges.
When use multiples of the polyatomic ions,
make sure that parentheses are placed around
it with a subscript outside of the parentheses
to show that more then one was used.
106739450
6
NAMING MOLECULAR COMPOUNDS
A molecule has covalent bonds. The name
and formula of a molecular compound
describe the type and number of atoms in a
molecule of the compound. The general rule
is that the most metallic element goes first. So
the element that appears the further left on the
periodic table goes first when writing the
formula. If the elements are in the same
group, the one closest to the bottom goes first.
As in naming ionic compounds, the second
element will use the root word of that element
with the suffix “ide” added to it. Unlike ionic
compounds, molecular compound names
reflect the ratios and type of elements in the
molecule. The elements’ names have a prefix
added that reflects the number of atoms in the
formula. The prefixes are on page 175. Mono
is usually not used for the first element. CO2 is
carbon dioxide.
106739450
7
WRITING MOLECULAR FORMULAS
When writing the molecular formulas, it is
easy. Use the symbols for the names of each
element in the formula followed by a subscript
that is equal to the prefix in the name.
For example diphosphorus tetrafluoride is P2F4
106739450
8
6.4
METALLIC BONDS
In metals, electrons are free to move
around the cations. The metals are gaining
and losing electrons continuously. Overall,
the metallic bonds are neutral because it
occurs at the same rate. A metallic bond is
the attraction between a metal cation and
the shared electrons that surround it. The
more valence electrons a metal have, the
stronger the metallic bonds. This explains
the properties among metals. The flexible
lattice structure of metallic bonds explains
the malleability of metals.
ALLOY
When metals are mixed together, an alloy
is formed. Alloys will have properties that
serve a more useful purpose than the pure
elements can. Gold is mixed with other
metals to make it harder and more durable.
24K gold is pure gold. 12 K gold is 50%
106739450
9
gold. Metal workers in Thailand were the
first to make bronze. When copper and tin
is mixed, bronze is formed. Copper and tin
are very soft in the elemental form but
when mixed, the bronze that is the result is
harder than either one of those elements.
Mixing zinc and copper forms brass.
When carbon is combined with iron, steel is
formed. The carbon atoms makes steel
harder and stronger than iron. When
chromium is added to steel, stainless steel
is created. Stainless steel won’t rust but it
is more brittle that steel. When aluminum
is used for aircraft, magnesium is added to
make it stronger and less malleable but still
keeping it lightweight.
106739450
10