Chemical Formulas and Bonding
Chapter 7
Ionic Bonding
• In an ionic bond, a positively charged ion is
attracted to a negatively charged ion.
– Ionic compounds are composed entirely of ions.
• Cations are positively charged ions
• Anions are negatively charged ions
• Ionic compounds are electrically neutral, so the
electrical charges of the cations and anions must
balance.
– Example: NaCl
• The Octet Rule – atoms tend to gain, lose, or
share electrons in order to acquire a full set of
valence electrons (8 in the s and p orbital, except
hydrogen and helium)
Electron moves here!
• Lewis Dot Diagrams or Electron Dot Diagrams
– Valence electrons are represented as dots
placed around the element symbol. Small x’s or
o’s can also be used instead of dots.
Sodium
• Types of Ions
– Monatomic Ions – made up of one atom
– Cations are named according to the element name
– Anions are named according to the element name, but add
“ide” to the end
• Monatomic cations and anions examples:
– Polyatomic ions – made from more than one
atom
• Polyatomic cations and anions examples:
– Binary Ionic Compounds – compound which contains
only two elements
• Empirical formula – ratio of ions in a compound
• Examples:
• Na+1 Cl-1  Na1+Cl1-  NaCl
• Ca+2 F–1  Ca+2 F–1  Ca1F2  CaF2
Covalent Bonding
• Formed by a shared pair of electrons between two
non-metal atoms
– Molecule – a group of atoms that are united by
covalent bonds
• Molecular substance – a substance that is made of
molecules
• Molecular formula – tells how many atoms are in a single
molecule of the compound.
• Structural Formula – specifies which atoms are bonded to
each other in a molecule
• Lewis structures – based on the Lewis dot diagrams for
atoms
• Lewis structures can
be drawn using either
dots or dashes.
– Each dot represents an
electron
– Dashes represent a pair
of electrons
– Lone pairs are electrons
that are not used in
covalent bonding.
– Bonding pairs are the
shared electrons
between atoms.
•
•
•
Ammonia NH3
made up of a covalent bond between nitrogen
and hydrogen
Each atom in the bond has a stable electron
configuration ~ hydrogen only needs 2 electrons,
but nitrogen needs 8.
Carbon tetrachloride CCl4
– Carbon and chlorine both have a stable
octet of electrons surrounding them.
• Multiple Bonds – bonds between atoms where
more than two electrons are shared
– Single covalent bond – one pair of electrons are
shared
– Double covalent bond – two pair of electrons
are shared
– Triple covalent bond – three pair of electrons
are shared
• Methane – single covalent bonds between
hydrogen and carbon
• Ethyl Alcohol, Ethanol C2H5OH– single covalent
bonds between hydrogen, carbon and oxygen
• Carbon dioxide – double covalent bond between
carbon and oxygen, giving each element an octet
• Oxygen gas – double covalent bond between
oxygen atoms, giving each an octet
..
..
..
..
• Cyanic acid – triple covalent bond between
carbon and nitrogen, giving each an octet.
Hydrogen only needs two to be stable!
..
• Nitrogen gas – triple covalent bond between
nitrogen atoms, giving each an octet.
..
..
• Nonpolar covalent bonds occur when atoms
exert an approximately equal pull on the electrons
in the bond.
• Exceptions to the octet rule cause bonding that
is unusual.
F
B
F
F
Naming Chemical Compounds
• Compounds are named according to the atoms
and bonds that compose it
• Ionic compounds are named based on the ions
that are involved
– Cations are named according to their element name
– Anions are named according to their element, but the
ending is changed to “ide” or polyatomic ion name
• Example: KI is called potassium iodide, not
potassium iodine
– Cu(NO3)2 is called copper II nitrate
• Molecular Compounds
are named similar to ionic
compounds, except for the
anion.
– First element is named
according to the element
name. If it has more than one
of that element, then you
must use a prefix
– Second element is named
according to the element
name, plus the “ide” ending,
but depending on the number
of atoms of that element, a
prefix must be used
• Example: CO2 is
called carbon
dioxide, because of
the 2 oxygen atoms
Prefix
MonoDiTriTetraPentaHexaHeptaOctaNonaDeca-
Number
1
2
3
4
5
6
7
8
9
10
• Naming acids depends on the ions that make up
the acid
– Diatomic compounds, such as HF, are named first by
hydro for the hydrogen, then fluoride for the fluorine
– However, fluoride is changed to fluoric, giving the
name hydrofluoric acid
– Acids containing polyatomic ions do not have hydro
as a prefix, but are named according to the polyatomic
ion
• The ending for the ion depends on the number of oxygen
atoms or the name of the polyatomic ion
• Example:
HNO3 is
called nitric
acid, but
HNO2 is
called nitrous
acid
• ate = ic
• ite = ous
• At the right
are common
acids and
their anions
Sulfate = sulfuric
Phosphate = phosphoric
Anion
Corresponding Anion Corresponding
acid
acid
F -,
fluoride
HF,
hydrofluoric acid
NO3-,
nitrate
HNO3,
nitric acid
Cl-,
chloride
HCl,
hydrochloric acid
H2CO3,
carbonic acid
Br-,
bromide
HBr,
hydrobromic acid
CO3-2,
carbon
ate
SO4-2,
sulfate
I-,
iodide
HI,
hydroiodic acid
S-2,
sulfide
PO4-3,
phosph
ate
H2S, hydrosulfuric C2H3O2
acid
,
acetate
H2SO4,
sulfuric acid
H3PO4,
phosphoric
acid
HC2H3O2,
acetic acid