IB CHEMISTRY:
TOPIC 4 BONDING NOTES
4.1 Ionic bonding and structure
Ions
• Atoms have a neutral charge as their negative electrons and positive protons balance out
• However, ions are formed when atoms gain or lose electrons
• The charge is changed by adding or removing electrons from an atom
• Cations are atoms that lose electrons and therefore have a positive net charge
• Therefore, positive ions are called cations
• Anions are atoms that gain electrons and therefore have a negative net charge
• Therefore, negative ions are called anions
Ionic Bonding
• Ionic bonds form as a result of the electrostatic attraction between oppositely
charged ions
o An electrostatic attraction is the attraction of oppositely charged of
particles/objects
• This bond only occurs between metals and non-metals
• The metal will have a positive charge (as it donates its electron to the non-metal), while
the non-metal will have a negative charge
• The opposite charges create an electrostatic attraction between the ions, causing
them to form a neutral lattice
• The charge of the ions will cancel each other out
Formation of an ionic compound
• When metals react with non-metals electrons are transferred from the metal to the non-
metal forming an ion
• Ionic compounds are balanced as the negative and positive charges balance each other
out
• The formation of an ionic compound
can be represented using electron
shell diagrams
• Example: When sodium and chlorine
react together to form sodium
chloride the electron that a sodium
atom loses to form a stable sodium
ion is gained by a chlorine atom to for
a stable chlorine ion
Chemical Charge
, • Remember, noble gas configuration is the most
stable so most elements will try to reach it by either
losing or gaining electrons
• To find the ionic charge of an element the periodic
table can be used:
• Group 1, 2, 3 elements form ions with charges
of 1+, 2+ and 3+ respectively
• Group 15, 16, 17 elements form ions with
charges of 3-, 2-, 1- respectively
• Elements in group 14 can lose 4 electrons but can also gain 4 electrons
Physical Properties of Ionic Compounds
• The electrostatic force of attraction between oppositely charged ions
arrange in a 3D structure called a lattice
• This is possible because the ions are held together by their opposite
charges, and each ion will be surrounded by 6 other different ions
• For the most stable arrangement positively charged ions are packed
as closely as possible to the negative charged ions, while ions of the
same charge are as far apart as possible. This maximizes electrostatic attraction
between the ions, while minimizing repulsion
• Under normal conditions, ionic compounds are usually solids with lattice
structures
• The lattice structure of an ionic compound can be used to explain their physical
properties
Volatility
• Volatility: The tendency of a substance to vaporize
• Ionic compounds have ionic bonds which are very strong meaning that a lot of energy is
needed to break its bonds. Thus at room temperature there isn’t enough energy to break
the lattice.
• Example: If you leave salt in a room for 100 years it will be the same, it won’t turn into a
gas because it’s non-volatile
• Therefore ionic compounds can be described as having a low volatility or being
non-volatile
High melting temperatures
• As mentioned before ionic bonds are very strong and a lot of energy is needed to break
its bond
• Hence ionic compounds have high melting temperatures
• Therefore Ionic compounds are solid at room temperature
• Melting point: Solid -> Liquid
• Boiling point: Liquid -> Gas
Electrical conductivity
• When ionic compounds are solid the ions are not free to move as there are held in fixed
positions so the ionic compound cannot conduct electricity when solid
TOPIC 4 BONDING NOTES
4.1 Ionic bonding and structure
Ions
• Atoms have a neutral charge as their negative electrons and positive protons balance out
• However, ions are formed when atoms gain or lose electrons
• The charge is changed by adding or removing electrons from an atom
• Cations are atoms that lose electrons and therefore have a positive net charge
• Therefore, positive ions are called cations
• Anions are atoms that gain electrons and therefore have a negative net charge
• Therefore, negative ions are called anions
Ionic Bonding
• Ionic bonds form as a result of the electrostatic attraction between oppositely
charged ions
o An electrostatic attraction is the attraction of oppositely charged of
particles/objects
• This bond only occurs between metals and non-metals
• The metal will have a positive charge (as it donates its electron to the non-metal), while
the non-metal will have a negative charge
• The opposite charges create an electrostatic attraction between the ions, causing
them to form a neutral lattice
• The charge of the ions will cancel each other out
Formation of an ionic compound
• When metals react with non-metals electrons are transferred from the metal to the non-
metal forming an ion
• Ionic compounds are balanced as the negative and positive charges balance each other
out
• The formation of an ionic compound
can be represented using electron
shell diagrams
• Example: When sodium and chlorine
react together to form sodium
chloride the electron that a sodium
atom loses to form a stable sodium
ion is gained by a chlorine atom to for
a stable chlorine ion
Chemical Charge
, • Remember, noble gas configuration is the most
stable so most elements will try to reach it by either
losing or gaining electrons
• To find the ionic charge of an element the periodic
table can be used:
• Group 1, 2, 3 elements form ions with charges
of 1+, 2+ and 3+ respectively
• Group 15, 16, 17 elements form ions with
charges of 3-, 2-, 1- respectively
• Elements in group 14 can lose 4 electrons but can also gain 4 electrons
Physical Properties of Ionic Compounds
• The electrostatic force of attraction between oppositely charged ions
arrange in a 3D structure called a lattice
• This is possible because the ions are held together by their opposite
charges, and each ion will be surrounded by 6 other different ions
• For the most stable arrangement positively charged ions are packed
as closely as possible to the negative charged ions, while ions of the
same charge are as far apart as possible. This maximizes electrostatic attraction
between the ions, while minimizing repulsion
• Under normal conditions, ionic compounds are usually solids with lattice
structures
• The lattice structure of an ionic compound can be used to explain their physical
properties
Volatility
• Volatility: The tendency of a substance to vaporize
• Ionic compounds have ionic bonds which are very strong meaning that a lot of energy is
needed to break its bonds. Thus at room temperature there isn’t enough energy to break
the lattice.
• Example: If you leave salt in a room for 100 years it will be the same, it won’t turn into a
gas because it’s non-volatile
• Therefore ionic compounds can be described as having a low volatility or being
non-volatile
High melting temperatures
• As mentioned before ionic bonds are very strong and a lot of energy is needed to break
its bond
• Hence ionic compounds have high melting temperatures
• Therefore Ionic compounds are solid at room temperature
• Melting point: Solid -> Liquid
• Boiling point: Liquid -> Gas
Electrical conductivity
• When ionic compounds are solid the ions are not free to move as there are held in fixed
positions so the ionic compound cannot conduct electricity when solid
