Bonding
Homework:
Bond Types Worksheet
Quiz on Friday
Test next Friday
Valence Electrons
• Valence electrons are the electrons in
the highest occupied energy level of an
element’s atoms.
• The number of valence electrons largely
determines the chemical properties of an
element.
• To find the number of valence electrons
in an atom you look at the last number in
the electron configuration.
The Octet Rule
• Octet rule: In forming compounds,
atoms tend to achieve the electron
configuration of a noble gas.
• -Metals tend to lose their electrons in
order to achieve a complete octet
• -Non-metals tend to gain or share
electrons in order to complete an octet
Formation of Cations
• The electron configuration of the
sodium ion is the same as that of a
neon atom.
• Na 2-8-1
• Na+ 2-8
• Ne 2-8
• Atoms want to get the electron
configuration of the nearest Noble Gas
Formation of Cations
• Cations of Group 1
elements always
have a charge of
1+. Cations of group
2 elements always
have a charge of
2+.
Formation of Anions
• Both a chloride ion and the argon
atom have an octet of electrons in
their highest occupied energy levels.
• Cl
2-8-7
• Cl- 2-8-8
• Ar
2-8-8
Energy and Chemical Bonds
• Chemical bonds are forces that hold
compounds together
• Energy is needed to overcome these
attractive forces and separate the atoms in
a compound
– Breaking a chemical bond is Endothermic
– Formation of a bond is Exothermic
• The less energy released when a bond is broken
the more stable the bond.
• Example:
– B + C  BC + 100 joules
– X + Y  XY + 400 joules
• Which bond is more stable?.
– The first bond is more stable
• Why?
– It is more stable because it releases less
energy.
Electronegativity
• Electronegativity – the attraction an atom has for
electrons
– Higher electronegativity the greater the attraction for
electrons
– Lower electronegativity the less attraction for
electrons
• Electronegativity differences in bond
– Greater the difference the more ionic in character,
until no longer sharing electrons, but electrons have
been transferred
• Difference of 1.7 or more = Ionic bond
• Difference of 1.6 or less = covalent bond
Distinguishing Bond Types
• To tell whether substance contains
metallic, covalent, or ionic bonds one has
to look at the properties (conductors,
melting/boiling points, hardness) and
remember:
– Metallic bonds = Metal
– Covalent = Nonmetals
– Ionic = Metal and Nonmetal
Conductivity
Bond Type Melting/
Boiling
Point
Hardness
Solid
Liquid
Aqueous
Metallic
High
Hard
Yes
Yes
Yes
Covalent
Low
Soft
No
No
No
Ionic
High
Hard
No
Yes
Yes
Formation of Ionic Compounds
• Compounds composed of cations and
anions are called ionic compounds.
–Although they are composed of
ions, ionic compounds are
electrically neutral.
Formation of Ionic Compounds
• Aluminum metal
and the
nonmetal
bromine react to
form an ionic
solid, aluminum
bromide.
Formation of Ionic Compounds
–Ionic Bonds
• The electrostatic forces that hold ions together in
ionic compounds are called ionic bonds.
Ionic Bonding
• Ionic bond is formed when ions bond
together because of the electrostatic
attraction of oppositely charged ions
• Key phrases to remember:
– Transfer of electrons
– Metal and Nonmetal
– Ions
– Electronegativity difference of 1.7 or greater
Ion Formation
• Metals
–
–
–
–
Lose electrons
Postively charged ions
Octet of electrons
Radii decreases
• Nonmetals
–
–
–
–
Gain electrons
Negatively charged ions
Octet of electrons
Radii increases
Formation of Ionic Compounds
– Animation 8 Take an atomic-level look at the
formation of KCl.
Formation of Ionic Compounds
–Formula Units
–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
compound.
Properties of Ionic Compounds
–Most ionic compounds are
hard crystalline solids at room
temperature.
–Ionic compounds generally
have high melting and boiling
points.
Properties of Ionic Compounds
• The orderly arrangement of component ions
produces the beauty of crystalline solids.
Properties of Ionic Compounds
– Simulation 5 Simulate the formation of ionic
compounds at the atomic level.
Properties of Ionic Compounds
–Ionic compounds can conduct an electric
current when melted or dissolved in water
because electrons are able to move.
Properties of Ionic Bonds
• High melting points and high boiling points
• Hard
• Conduct heat and electricity when in the
liquid and aqueous phase
– Electrons are able to move