1
ELEMENTS, COMPOUNDS, AND CHEMICAL BONDING
Chapter 7…Ionic and Metallic Bonding
VALENCE ELECTRONS AND BONDING
Mendeleev used similarities in the properties of elements to organize his periodic table. Later we realized
that elements in the same group behave similarly because they have the same number of valence
electrons. Recall that these are electrons in the highest occupied energy level of an element’s atom.
Electron dot diagrams (aka Lewis dot diagrams) illustrate the valence electrons as dots around the
chemical symbol of the atom. This model helps us to understand the formation of bonds.
Valence electrons are usually the only electrons used in chemical bonds. According to the octet rule,
when forming compounds atoms tend to achieve the electron configuration of a noble gas (i.e., eight
electrons in the outer shell). This is due to their valence shell being composed of the “s” and “p”
sublevels which can hold eight electrons in total. The exception to this is hydrogen as it can only have a
maximum of two valence electrons, just like helium, because it only has an “s” sublevel to fill.
When bonding occurs, compounds are formed and a chemical formula can be written. A chemical
formula shows the kinds and numbers of atoms in the smallest representative unit of a compound (ex.
NaCl, is the chemical formula for sodium chloride). States of matter can be indication in a chemical
formula as a subscript in brackets at the end of the formula. These states are: (s) for solid, (l) for liquid,
(g) for gas, and (aq) for aqueous (dissolved in water).
Science communication must be international, logical, precise, and simple. There is a traditional naming
system when writing chemical names for a compounds and there is a more modern system designed by
IUPAC. Some chemists may still use the traditional naming system, but you should be primarily be aware
of IUPAC nomenclature.
IONIC BONDS AND IONIC COMPOUNDS
Atoms of metals tend to become cations because they lose their valence electrons; this leaves the ion
with a positive charge and a complete octet in the next lowest energy level. Atoms of some non-metals
tend to become anions because they gain valence electrons to complete their octet and this leaves them
with a negative charge.
Compounds that are composed of cations and anions are called ionic compounds. These ions tend to
be a metal cation joined with a nonmetal anion. Ionic bonds form as a result of this TRANSFER of
valence electrons; it is the resulting ionic charges that cause an attraction and the bond itself. Although
ionic compounds are composed of ions, they are electronically neutral because the charges of the ions
balance out. Within upcoming examples, this is evident as the net electrical charge in a chemical formula
must equal ZERO.
Most ionic compounds are crystalline solids at room temperature and have high melting points. When
added to water they completely dissociate into their individual ions. They are considered electrolytes
because they can conduct an electric current when melted or dissolved in water because of the presence
of the ions.
Chapter 9…Chemical Names and Formulas
There are five types of ionic compounds:
(1) Binary ionic compounds are made up of monatomic ions (ions that are the result of a single
atom). When writing chemical formulas, you must (a) predict the charges of the individual ions, and
(b) decide how many of each ion is needed so that the sum of the positive and negative ion charges
is zero (balanced). When naming them, name the cation in full followed by the name of the anion,
with its ending changed to “ide”. Consider the following examples:
Cation
Anion
Chemical Formula
Net charge
Chemical Name
Na+
ClNaCl
(1+) and (1-) = 0
sodium chloride
Ca2+
ClCaCl2
(2+) and 2(1-) = 0
calcium chloride
2
Al3+
Na+
Al3+
Ca2+
ClS2S2S2-
AlCl3
Na2S
Al2S3
CaS
(3+) and 3(1-) = 0
2(1+) and (2-) = 0
2(3+)and 3(2-) = 0
(2+) and (2-) = 0
aluminum chloride
sodium sulfide
aluminum sulfide
calcium sulfide
(2) Ionic compounds containing polyatomic ions are made up of a cation or anion that is composed of a
group of atoms with a net positive or negative charge. They are found in a table on the back of the
periodic table. When writing chemical formulas, you must include brackets around the polyatomic ion
when more than one is required to balance the charges. When naming them, both the cation and
anion are named in full – there are no changes to their names. Consider the following examples:
Cation
Anion
Chemical Formula
Net charge
Chemical Name
K+
CO32K2CO3
2(1+) and (2-) = 0
potassium carbonate
Al3+
SO32Al2(SO3)3
2(3+) and 3(2-) = 0
aluminum sulfite
+
NH4
PO43(NH4)3PO4
3(1+) and (3-) = 0
ammonium phosphate
(3) Ionic compounds containing multivalent metals (aka polyvalent metals) are made up of metals that
form more than one ion, each with its own particular charge. These metals are found within the
transition metals and their possible ionic charges can be found on the back of the periodic table.
Writing chemical formulas for these ionic compounds is the same as the others, but naming them
requires a roman numeral to identify which cation is involved. Consider the following examples:
Cation
Anion
Chemical Formula
Net charge
Chemical Name
Fe2+
O2FeO
(2+) and (2-) = 0
iron(II) oxide
Fe3+
O2Fe2O3
2(3+) and 3(2-) = 0
iron(III) oxide
(4) Hydrates are ionic compounds that decompose at relatively low temperatures to produce water and
an associated compound. Water is loosely held by the ionic compound and when it is removed the
substance is referred to as anhydrous. Writing the chemical formulas is the same for other ionic
compounds except for at the end there is a dot (•) followed by a number of water molecules. The
naming of hydrates requires the prefexes from 1 to 10 as listed in table 9.4 on p. 269 (mono, di, tri,
tetra, penta, hexa, hepta, octa, nona, deca). Consider the examples below:
Chemical Formula
Chemical Name
CuSO4 • 5H2O
copper(II) sulfate pentahydrate
Fe(NO2)3 • 9H2O
iron(III) nitrite nonahydrate
(5) Acids and bases involve ionic bonds although they may or may not involve a metal. Acids have H+
as the cation and bases have OH- as the anion. As an indicator of acidity and alkalinity (whether
something is an acid, a base, or neither), acids will turn blue litmus paper red and bases with turn red
litmus paper blue. Acids and bases resemble molecular compounds (*explained on the next page),
but when dissolved in water, they conduct electricity like ionic compounds and become an “active”
acid or base. Acids have separate naming rules (see table 9.5 on page 272, and see the back of the
period table) and should have (aq) written as a subscript at the end of the chemical formula to
indicate that it is dissolved in water. Bases are named like any other ionic compound that has a
polyatomic ion in it. Consider the examples below:
Chemical Formula
Chemical Name
Acid or base?
HCl(aq)
hydrochloric acid
Acid
HBr(aq)
hydrobromic acid
Acid
HClO2(aq)
chlorous acid
Acid
HNO3(aq)
nitric acid
Acid
H2SO4(aq)
sulfuric acid*
Acid
H3PO4(aq)
phosphoric acid*
Acid
NaOH(aq)
sodium hydroxide
Base
Ba(OH)2(aq)
barium hydroxide
Base
NH4OH(aq)
ammonium hydroxide
Base
*small exception to the naming rules
METALLIC BONDS AND METALLIC COMPOUNDS
Metals are made up of closely packed cations rather than neutral atoms. The valence electrons are
mobile and can drift freely form one part of the metal to another. Metallic bonds consist of the attraction
3
of the free-floating valence electrons for the positively charged metal ions. Alloys are generally
homogeneous metallic mixtures composed of two or more metals. They are important because their
properties are often superior to those of their individual parts (Ex. Brass is made of copper and zinc, steel
is made of iron and carbon).
Chapter 8…Covalent Bonding
COVALENT BONDS AND MOLECULAR COMPOUNDS
Atoms in molecular compounds are held together by the SHARING of valence electrons creating a
covalent bond. A molecule is a neutral group of atoms joined together by covalent bonds. A
compound composed of covalent bonds is called a molecular compound (aka covalent compounds).
A molecular formula is another name for a chemical formula specific to molecules.
Molecular compounds tend to be two non-metal elements joined together. They tend to be solids, liquids
and gases at room temperature. Molecular compounds tend to have relatively lower melting and boiling
points than ionic compounds. They generally don’t conduct an electric current when melted or dissolved
in water (non-electrolytes).
Chapter 9…Chemical Names and Formulas
There are three types of molecular compounds:
(1) Molecular elements are technically still considered an element because they are composed of
atoms of the same element. Diatomic elements (molecules made of two atoms) are stabilized by
being covalently bonded with another atom of that element and they exist this way in nature when
they are not part of another kind of compound. The seven diatomic elements are H 2, N2, O2, Cl2, Br2,
F2, and I2. There are three special polyatomic elements and they are O3 (ozone or trioxygen), S8
(octasulfur), and P4 (tetraphosphorous).
(2) Binary molecular compounds contain two nonmetal elements and are named using Greek
numerical prefixes found in table 9.4 on page 269 (mono, di, tri, tetra, penta, hexa, hepta, octa, nona,
deca). When naming these molecules, a prefix is used to indicate the number of atoms, but the prefix
“mono” is not required when there is only one atom of the first element. Also, the name of the first
element listed doesn’t change, but the ending of the second element changes to “ide”. Consider the
examples below:
Chemical Formula
Chemical Name
CS2
carbon disulfide
N2O
dinitrogen oxide
P4O10
tetraphosphorous decaoxide
CO
carbon monoxide
(3) There are molecular compounds that have more than two types of nonmetals bonded together.
EXCEPTION: Although hydrogen is a nonmetal and can be bonded to other nonmetals, note that
hydrogen compounds are an exception to the rules and they do not use the prefix system. H is both a
cation and an anion.