IV. Chemical Bonding
Compounds can be
differentiated by their chemical
and physical properties.
(3.1dd)
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Two major categories of
compounds are ionic and
molecular (covalent) compounds.
(5.2g)
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 Ionic compounds are
 Molecular compounds
formed when a metal
combines with a
nonmetal.
 Ionic compounds have
ionic bonds.
are formed between
two nonmetals.
 Molecular compounds
have covalent bonds.
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Regents Question: 06/02 #3
Which compound contains ionic bonds?
(1) NO
Nitrogen – nonmetal
(2) NO2
Oxygen – nonmetal
(3) CaO
Calcium – metal
(4) CO2
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Carbon – nonmetal
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Regents Question: 08/02 #11
Which formula represents an ionic compound?
(1) NaCl
(2) N2O
(3) HCl
(4 )H2O
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Chemical bonds are formed
when valence electrons are
(5.2a):
 transferred from one atom to another
(ionic)
 shared between atoms (covalent)
 mobile within a metal (metallic)
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Ionic bonds are formed when metals
transfer their valence electrons to
nonmetals.
The oppositely charged ions attract
each other to form an ionic bond.
Sodium has one valence electron and chlorine has seven.
Sodium want to lose 1 electron and chlorine needs to gain 1.
Sodium transfers its valence electron to chlorine
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Forming an Na+ and a Cl- ion – sodium chloride NaCl
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Additional atoms may be
necessary to insure that all the
ions formed have a stable (noble
gas) electron configuration.
What happens when aluminum combines
with oxygen to make aluminum oxide?
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Regents Question: 06/02 #12
Which species does not have a noble gas electron
configuration?
(1) Na +
(2) Mg 2+
(3) A r
(4) S
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Aluminum want to lose its 3 valence
electrons. Oxygen needs to gain 2
electrons.
The number of electrons lost by the metal must equal the
number of electrons gained by the nonmetal
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The formula of aluminum oxide
is Al2O3.
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Comparing the properties
compounds with ionic bonds and
compounds with covalent bonds.
 Properties of ionic
compounds
– Solids with high melting
and boiling points (strong
attraction between ions)
– Electrolytes: Do not
conduct electricity as solids
but do when dissolved or
molten – ions are charged
particles that are free to
move
– No individual molecules
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 Properties of molecular
compounds
– Low melting and boiling
points (weak attraction
between molecules)
– Nonelectrolytes: Do not
conduct electricity as solids
or when dissolved or molten
– no charged particles (ions)
to move
– Solids are soft
– Forms molecules
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Ionic solids conduct electricity
when dissolved or molten.
Molecular solids do not.
Solution
doesn’t conduct
electricity
Solution
conducts
electricity
Ionic Solid
dissolved in water
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Molecular Solid
dissolved in water
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Regents Question: 01/03 #35
Which of the following solids has the highest melting
point?
(1) H2O(s)
(2) Na2O(s)
(3) SO2 (s)
(4) CO2 (s)
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Regents Question: 06/02 #61-63
Testing of an unknown solid shows that it has the
properties listed below.
(1) low melting point
(2) nearly insoluble in water
(3) nonconductor of electricity
(4) relatively soft solid
State the type of bonding that would be expected in
Covalent
the particles of this substance.
Explain in terms of attractions between particles why
the unknown solid has a low melting point.
The attraction between particles is weak because there are no
charged particle.
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Explain why the particles of this substance are
Molecular substances are nonnonconductors of electricity.
electrolytes – they do not form ions.
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When nonmetals combine with
nonmetals, they share electrons.
The attraction of two atoms for a
shared pair makes a covalent bond.
•Electrons are always shared in pairs.
•Sharing electrons fills the valence shell with
8 electrons (2 for hydrogen.)
Hydrogen chloride
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water
ammonia
methane
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Regents Question: 06/03 #12
Which type of chemical bond is formed between
two atoms of bromine?
(1) Metallic
(2) Hydrogen
(3) ionic
(4) covalent
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In a multiple covalent bond,
more than one pair of
electrons are shared between
two atoms. (5.2e)
•Diatomic oxygen has a double bond O=O (2 shared pairs)
because oxygen needs 2 electrons to fill its valence shell
•Diatomic nitrogen has a triple bond NN (3 shared pairs)
because nitrogen needs 3 electrons to fill its valence shell
•Carbon dioxide has two double bonds
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Regents Question: 08/02 #17
Which molecule contains a triple covalent
bond?
(1) H 2
(2) N 2
(3) O 2
(4) Cl 2
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Molecular polarity can be determined
by the shape of the molecule and the
distribution of charge.
 Possible shapes
– Linear
(X2 HX CO2)
– Bent
(H2O)
– Pyramidal
(NH3)
– Tetrahedral (CH4 CCl4)
A polar molecule is called a dipole. It has a positive
side and a negative side – uneven charge distribution.
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Symmetrical (nonpolar)
molecules include CO2 , CH4 ,
and diatomic elements. ..
Symmetrical molecules are not dipoles.
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Asymmetrical (polar)
molecules include HCl, NH3 ,
and H2 O. (5.2l)
The negative side of the molecule is the side that has the
atom with the higher electronegativity.
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When an atom gains one or
more electrons, it becomes a
negative ion and its radius
increases. When an atom
loses one or more electrons, it
becomes a positive ion and its
radius decreases. (5.2c)
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Regents Question: 06/02 #10
Compared to the radius of a chlorine atom, the
radius of a chloride ion is
(1) larger because chlorine loses an electron
(2) larger because chlorine gains an electron
(3) smaller because chlorine loses an electron
(4) smaller because chlorine gains an electron
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Regents Question: 08/02 #23
Which electron configuration is correct for a
sodium ion?
(1) 2–7
(2) 2–8
(3) 2–8–1
(4) 2–8–2
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Regents Question: 01/03 #14
Given the equation:
This equation represents the formation of a
(1) fluoride ion, which is smaller in radius than a
fluorine atom
(2) fluoride ion, which is larger in radius than a
fluorine atom
(3) fluorine atom, which is smaller in radius than
a fluoride ion
(4) fluorine atom, which is larger is radius than a
fluoride ion
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When a bond is broken,
energy is absorbed. When a
bond is formed, energy is
released. (5.2i)
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Atoms attain a stable valence
electron configuration by
bonding with other atoms.
Noble gases have stable
valence configurations and
tend not to bond. (5.2b)
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Physical properties of
substances can be explained
in terms of chemical bonds
and intermolecular forces.
These properties include
conductivity, malleability,
solubility, hardness, melting
point, and boiling point. (5.2n)
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The stronger the intermolecular
forces, the higher the boiling
points and melting points.
Strongest
 Ionic Solids
 Molecules with Hydrogen bonds
 Polar molecules
 Nonpolar molecules
Weakest
For nonpolar molecules, the greater the mass, the greater
the force of attraction.
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Regents Question: 08/02 #33
The table below shows the normal boiling point of four
compounds.
Compound
HF (l)
Normal
Boiling Point (°C)
19.4
CH3Cl (l)
–24.2
CH3F (l)
–78.6
HCl (l)
–83.7
Which compound has the strongest intermolecular
forces?
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(1) HF(l)
(2) CH Cl(l)
(3)CH F(l)
(4)HCl(l)
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Electron-dot diagrams (Lewis
structures) can represent the
valence electron arrangement
in elements, compounds, and
ions. (5.2d)
atom
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ion
molecular
compound
ionic
compound
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Dots represent valence electrons.
Everything else (inner shell
electrons and nucleus) is called
the Kernel and is represented by
the symbol.
Phosphorous has 5 valence electrons so we draw 5 dots
around the symbol for phosphorous.
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Regents Question: 06/03 #11
What is represented by the dots in a Lewis electrondot diagram of an atom of an element in Period
2 of the Periodic Table?
(1) the number of neutrons in the atom
(2) the number of protons in the atom
(3) the number of valence electrons in the atom
(4) the total number of electrons in the atom
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The correct order to fill in the
dots is to make a pair from the
first 2 electrons then we fill in
one on each side before we pair
up.
1 2
5
8
Ne
4
3
6
7
It does not matter which side you start from.
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The correct order to fill in the
dots is to make a pair from the
first 2 electrons then we fill in
one on each side before we pair
up.
5
7
4
8
Ne
1
2
6 3
This will let you know how many electron pairs and how
many unpaired electrons are in the atom’s valence shell
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Draw the Lewis Dot Structures of
the first 18 elements.
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When metals lose electrons to
form ions, they lose all their
valence electrons. The Lewis Dot
Structure of a metal ion has no
dots. The charge indicates how
many electrons were lost.
Magnesium atom Magnesium ion
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When nonmetals gain electrons,
they fill up their valence shell
with a complete octet (except
hydrogen.) The ion is placed in
brackets with the charge outside
the brackets.
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A + metal ion is attracted to a
– nonmetal ion (opposites attract)
forming an ionic compound. We
can use Lewis dot structures to
represent ionic compounds.
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The formula for magnesium fluoride is MgF2
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Regents Question: 06/02 #51-53
Draw the electron-dot (Lewis) structure of an atom of
calcium.
Draw the electron-dot (Lewis) structure of an atom of
chlorine.
Draw the electron-dot (Lewis) structure of calcium
chloride.
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Regents Question: 08/02 #53
Draw an electron-dot diagram for each of the following
substances:
A calcium oxide (an ionic compound)
B hydrogen bromide
C carbon dioxide
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Electronegativity indicates
how strongly an atom of an
element attracts electrons in a
chemical bond.
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Electronegativity values are
assigned according to
arbitrary scales. (5.2j)
Fluorine is assigned the value 4.0 – the highest of any element
Nonmetals have high electronegativity – they want to attract
electrons so they can fill their valence shell
Metals have low electronegativity – they want to lose
electrons to get rid of their valence shell
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Regents Question: 01/03 #10
The strength of an atom’s attraction for the
electrons in a chemical bond is the atom’s
(1) electronegativity
(2) ionization energy
(3) heat of reaction
(4) heat of formation
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The electronegativity difference
between two bonded atoms is
used to assess the degree of
polarity in the bond. (5.2k)
 Polar covalent bonds form between two different
nonmetals
 Polar bonds have a negative side and a positive
side
 The electrons are attracted more to the atom with
the higher electronegativity.
 The atom with the higher electronegativity is the
negative side of the bond.
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Regents Question: 06/03 #13
Which of these formulas contains the most polar
bond?
(1) H–Br
(2) H–Cl
(3) H–F
(4) H–I
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Three types of bonds
Ionic bonds– transfer of electrons- occur between a
metal and a nonmetal
Polar bonds– unequal sharing- occur between two
different nonmetals
Nonpolar bonds– equal sharing- occur between two
of the same nonmetals
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Metals tend to react with
nonmetals to form ionic
compounds. Nonmetals tend
to react with other nonmetals
to form molecular (covalent)
compounds. Ionic compounds
containing polyatomic ions
have both ionic and covalent
bonding. (5.2h)
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Polyatomic ions are groups of
atoms covalently bonded
together that have a negative
or positive charge.
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Polyatomic ions are held together
by covalent bonds but form ionic
bonds with other ions.
H
Covalent
bonds
H N H
+
Cl
Ionic bond
-
H
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The bonds holding metals
together in their crystal lattice are
called metallic bonds.
 All metals have metallic bonds
 “Positive ions immersed in a sea of mobile
electrons”
– Bonds are between Kernels, leaving the valence
electrons free to move from atom to atom
– Mobile electrons give metals the ability to
conduct electricity
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Regents Question: 06/02 #8
Metallic bonding occurs between atoms of
(1) sulfur
(2) copper
(3) Fluorine
(4) carbon
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Regents Question: 01/03 #15
The high electrical conductivity of metals is
primarily due to
(1) high ionization energies
(2) filled energy levels
(3) mobile electrons
(4) high electronegativities
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Regents Question: 06/03 #33
Which substance contains metallic bonds?
(1) Hg(l)
(2) H2O(l)
(3) NaCl(s)
(4)C6H12O6(s)
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Regents Question: 01/03 #39
A chemist performs the same tests on two
homogeneous white crystalline solids, A and B. The
results are
shown in the table below.
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The results of these tests suggest that
(1) both solids contain only ionic bonds
(2) both solids contain only covalent bonds
(3) solid A contains only covalent bonds and
solid B
contains only ionic bonds
(4) solid A contains only ionic bonds and
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Regents Question: 01/03 #57-60
Each molecule listed below is formed by sharing electrons between
atoms when the atoms within the molecule are bonded together.
Molecule A: Cl2
Molecule B: CCl4
Molecule C: NH3
Draw the electron-dot (Lewis) structure for the NH3 molecule.
Explain why CCl4 is classified as a nonpolar molecule.
It is symmetrical. There is an even charge distribution around the molecule.
Explain why NH3 has stronger intermolecular forces of attraction
than Cl
2 .hydrogen bonds, chlorine is nonpolar.
Ammonia
has
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Explain how the bonding in KCl is different from the bonding in
KCl molecules
is ionic and A,
molecules
A, B and C are molecular with covalent bonds.57
B, and C.