Topic 4: Bonding & Electric Chemistry
There are over 110 chemical elements, yet there are millions of possible
chemical compounds. When atoms combine chemical bonds form.
The elements are split into 2 distinct groups; Metals & Non-Metals.
Noble gases are unreactive because they have a stable electron arrangement i.e.
a full outer energy level, Neon 2, 8
Atoms react in order to achieve a stable electron arrangement
There are 3 types of chemical bond:
Metallic Bonds –
form between metal atoms
Covalent Bonds -
form between non-metal atoms
Ionic Bonds
form between metal atoms and non-metal atoms
-
Ionic
A metal atom loses its outer electrons, to achieve a stable electron arrangement
Na
2, 8, 1

Na+
2, 8 (like Neon 2, 8)
When a metal atom loses electrons, it is no longer neutral.
There are more positively charged protons than negatively charged electrons,
thus a __________ ____ is formed. When a particle loses electrons, it is
said to be ___________.
Non-metal atoms gain outer electrons, to achieve a stable electron arrangement
Cl
2, 8, 7

Cl-
2, 8, 8 (like Argon 2, 8, 8)
When a non-metal atom gains electrons, it now has more negatively charged
electrons than positively charged protons, thus forms a ________________
When a particle gains electrons, it is said to be ____________.
OIL RIG
Oxidation Is Loss : Reduction Is Gain
Thus when sodium atoms react with chlorine atoms, sodium donates electrons to
the chlorine, forming a positive sodium ion and a negative chloride ion, which are
attracted to each other. This attraction between ions is an Ionic Bond.
 Na (2,8,1) + Cl (2,8,7) 

 Na+ (2, 8) Cl- (2, 8, 8) 
Since million of atoms are involved in any reaction, then millions of ions are
formed. These oppositely charged ions arrange themselves into a large
structure called an __________________
Diagrams of ionic lattices
Metallic
In metals and alloys (a mixture of metals), the metal atoms are held together by
metallic bonds. A piece of iron has millions of iron atoms held together by
metallic bonds.
Metal atoms lose electrons to achieve a stable electron arrangement. Thus
metal atoms have a loose hold of their outer electrons. As such, in a piece of
metal, the outer electrons of each atom are able to move around, since the
nuclei of neighbouring atoms attract these loosely held electrons. These
electrons are said to be “Delocalised”.
Definition of a Metallic bond
Covalent
Non-metal atoms need to gain electrons, in order to obtain a stable electron
arrangement e.g.
Fluorine
F
2, 7
When 2 Fluorine atoms combine, they are not both able to gain electrons,
therefore they must __________ their outer electrons
Now both Fluorine
atoms have a share of
8 electrons in their
outer energy levels.
The Fluorine atoms are held together in a molecule because of the attraction
each nucleus has for the shared electrons.
Bonding Properties
Melting Point and Boiling Point
Metals and alloys contain metallic bonds. They both have ______ melting points
and boiling points, therefore metallic bonds are __________.
Ionic compounds e.g. sodium chloride, have high melting points, therefore ionic
bonds are __________.
There are 2 types of covalent structures
____________ e.g. water or methane
______________ e.g. diamond(C)
H2O – Water, m.pt = 0 C
C – Diamond, m. pt = 3642 C
Water has a very low boiling point, since
there are no obvious bonds between the
molecules. Weak Van Der Waals forces
exist between molecules. However, strong
bonds exist between the atoms, otherwise
water would break up into hydrogen &
oxygen when heated.
Diamond, a form of carbon, has strong
covalent bonds throughout its
structure. It has a high m. pt, since a
lot of energy is needed to break the
strong bonds.
Solid compounds can be either ionic or covalent compounds.
However if a compound is a liquid or gas at room temperature, then it is covalent
Electrical Conductivity
“Electricity is a flow of charged particles”
In all of the 3 types of chemical bonding, electrons are involved.
Metallic – contains delocalised electrons that are free to move around.
Ionic – No free electrons, since both ions have stable electron arrangements.
Covalent – No free electrons, since electrons are shared between atoms.
Conductivity of Solids
Only solid metals and carbon, in graphite form, conduct electricity, since they
have free (delocalised) electrons. In metal or graphite, electrical current is
carried by a flow of ___________.
NO SOLID COMPOUND, IONIC OR COVALENT, CONDUCTS ELECTRICITY.
Conductivity of Solutions/Melts
Ionic compounds and some covalent compounds dissolve in water to form
solutions. Only _________ solutions conduct electricity. When an ionic
compound dissolves in water, the strong ionic lattice holding the ions together,
is broken. The charged ions are now free to move.
When an ionic compound is melted e.g. molten lead bromide, the lattice is broken
and the ions are again free to move, thus it conducts electricity also.
In an ionic solution or melt, electrical current is carried by a flow of ______.
Evidence for the existence of ions - Electrolysis
The existence of ions can be shown by electrolysis (breaking up, using electricity).
Electricity is passed through blue copper(II)
chloride solution. After a few minutes,
red/brown copper metal is formed at the
negative electrode and bubbles of chlorine
gas are formed at the positive electrode.
At positive electrode
At negative electrode
Therefore, copper ions must have a
_____________ charge (Cu2+), if they are
attracted to the negative electrode.
Likewise, chloride ions must have a
______________ charge (Cl-), if they are
attracted to the positive electrode.
Covalent compounds contain no delocalised electrons or ions i.e. no charged
particles, therefore they do not conduct in any state.
Evidence for the Existence of Ions - Ion Colours
Many transition metal ions are coloured e.g. copper ions (Cu2+) are blue and
chromate ions (CrO4-) are yellow. Copper chromate is brown, due to the
presence of the blue and yellow ions. When copper chromate is electrolysed,
yellow dichromate ions move towards the positive electrode and blue copper ions
move towards the negative electrode.
Solubility
All ionic solids dissolve in _________, most covalent solids do not.
Covalent solids dissolve in “non-aqueous” solvents, like acetone; ionic
compounds do not.
Water is a “polar” covalent molecule, since the oxygen has more protons in its
nucleus, it has a bigger attraction for the shared electrons in the molecule.
Therefore the oxygen has a slight negative charge and each hydrogen has a
slight positive charge. These slight charges are attracted to the ions in the
ionic lattice. This attraction causes the lattice to be broken, so the solid
dissolves.
Ionic Lattice Dissolving
Polar water molecules attracted
to Na+ & Cl- ions
Bonding Summary
Type of Bond
Melting Point
Metallic
Simple Covalent
Covalent Network
High
Low
Conducts when molten/in
solution
High
Conducts when
solid
Yes
No
No
No
Yes
No
Making Electricity
Metals lose electrons to achieve a stable electron arrangement. When we
control this flow of electrons, it is called an electric current.
We can create an electrical current in a cell using 2 different metals and an
ionic solution. The ionic solution conducts electricity since it has free ions. We
call a solution that conducts electricity, an _____________.
The Electrochemical Series (ECS) – data book p7
When different metal pairs are used in a cell, different sizes and directions of
electrical current were observed. Cells are rated by their VOLTAGE , not their
current. Voltage is the force that a cell produces to push the ________
around the circuit.
Metal Pairing
High Voltage
Direction of Electron Flow
Mg & Cu
Mg  Cu
Al & Cu
Al  Cu
Fe & Cu
Fe  Cu
Sn & Cu
Sn  Cu
Low Voltage
1. Direction of Electron flow – Electrons flow from a metal higher in the ECS to a metal lower down.
2. Size of the Voltage – The further apart the 2 metals are in the ECS, the higher the voltage obtained
The Zinc/Copper Cell
This cell is made of two “half-cells”. These half-cells are
connected by an salt/ion bridge.
The purpose of this bridge is __________________________.
Each half cell consists of a piece of metal, dipped into a solution
of its own ions. Zn/Zn2+ and Cu/Cu2+
Electrons flow from the zinc to the copper, thus zinc loses electrons:
Zn(s)  Zn2+(aq) + 2e-
OXIDATION
At the positive electrode, positive copper ions gain these electrons
Cu2+(aq) + 2e-  Cu(s)
REDUCTION
Oxidation and Reduction must take place together, if a particle loses electrons
then another particle must gain them. These ion-electron equations for the
oxidation and reduction reactions can be combined in a REDOX equation.
Ion-Electron Equations
Zn(s)  Zn2+(aq) + 2e-

REDOX equation
Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)
Cu2+(aq) + 2e-  Cu(s)
Note:
Electrons are not shown in a REDOX equation, as the electrons on each side of the arrow cancel each other
Batteries
The reactions above are similar to those that occur in batteries. Batteries are
made up of a number of these cells. Batteries are a store of chemical energy.
In batteries, CHEMICAL ENERGY  ______________ ENERGY
Batteries can be rechargeable or non-rechargeable.
A LEAD-ACID battery, is an example of a ____________ battery.
Charging these batteries restores the chemical energy in them, so they are able
to be used over and over again.