Atoms combining
● An element is a substance which only contains one kind of atom
● A compound is made up of multiple elements chemically bonded together
● A mixture contains different substances that are not chemically bonded together
● Chemical change
○ When a new substance is formed and the reaction is irreversible
○ Signs of chemical change
■ One or more chemical substances are formed
■ Energy is taken in or given out, during the reaction
■ The change is usually difficult to reverse
● If no new chemical is formed, it is known as a physical change
● Ions
○ An ion is a charged particle. It is charged because it has an unequal number of protons and
electrons
○ If it has charge of 1+ then its a positive ion
○ If it has charge of 1- then its a negative ion
● Ionic bonds
○ Bonds formed between positive and negative ions is called an ionic bond
○ It is formed because of the transfer of electrons from metal to non-metal. Metals get a
positive charge(transfer) and nonmetal get negative ions(acceptance)
● Ionic compound
○ A metal reacts with a non-metal to form a ionic compound
○ Electrostatic forces of attraction between ions are very strong because they are very
stable compounds
● Properties of ionic compound
○ Able to conduct electricity in the molten or aqueous state because of the presence of ions
○ They don't conduct electricity in solid state as they do not have free electrons
○ Electrons are present in solids
○ Ions are present in aqueous, liquid or molten solutions
■ Molten → liquified by heat
■ Aqueous → dissolved in water
● Ionic bonds are soluble in water
● Bonding with LiF(Lithium fluoride)
○ LiF has a very high melting point as a lot of energy is needed to break the high
electrostatic forces of attraction between the ions
○ LiF is soluble in water
○ LiF does not conduct electricity in solid state because in solid state, LiF does not contain
free electrons
○ It conducts electricity in
aqueous state
Bonding with MgCl2
● Rules for drawing dot and cross diagram
○ Always draw the nucleus with the symbol of the element
○ Write the electronic configuration
○ Don't forget the charges
○ Never leave an empty shell
○ Draw all the shells(unless specified in question)
○ Draw a key of different symbols representing the +ve and -ve ions
● Covalent bonding
○ A covalent bond consists of a shared pair of
electrons with electrons being supplied by each
atom, either side of the bond
○ Properties
■ No transfer of electrons, electrons are shared
■ No inner shells, each pair of shared electrons form a bond
■ Both octet and duplet rules are satisfied and the atoms are stable
○ Covalent bonding between the atoms in each molecule is strong. Bonding between individual
molecules is not covalent and is weak
○ Covalent bonds don't dissolve in water nor are they soluble
Hydrogen
● Covalent bond
● Represented as H-H
● Linear shape
Methane - CH4
Oxygen
● Double bond(2 lines)
● Bond energy = 408 kJ/M
● Bond energy is the energy required to break
down the bonds
Nitrogen
● Triple bond(3 lines)
● Bond energy = 946 kJ/M
● Thus 78% of the atmosphere is nitrogen
● Properties of simple/covalent molecules
○ Appearance
■ In room temperature, simple molecules are gases, liquids or solids with low melting
and boiling points
○ Melting point
■ Very low
■ Weak attractive forces between molecules means that very less energy is needed
to break their bonds
○ Electricity
■ Don’t conduct electricity because they have no mobile ions or electrons
○ Almost opposite to Ionic Bonds
● Giant covalent molecules
○ In giant covalent molecules there are many atoms joined together in a regular arrangement
by a very large number of covalent bonds
○ Can result in a lattice structure
● General properties of giant covalent molecules
○ Melting point
■ Very high
■ Structure is made up of a large number of covalent bonds, al of which need to be
broken if atoms are to be separated
○ Electrical
■ Don’t conduct electricity because they have no mobile ions or electrons
● Giant molecules → macromolecules → covalent networks
Giant covalent molecules
● Diamond
○ Very high M.P. → many covalent bonds must be broken to separate atoms
○ Very strong → Each carbon atom is joined to 4 others in a rigid structure. Coordination no.
= 4(number of atoms, molecules, ions bonded to it)
○ Non-conductor of electricity → all four carbon atoms are used for bonding
○ Tetrahedral shape
○ All electrons are bonded
○ No free electrons
○ Does not conduct electricity
● Graphite
○ Hexagonal shaped
○ Are connected by weak Van Der Waals forces (connect the 2 layers)
○ Melting point is very high → many covalent bonds must be broken to separate atoms
○ Strength is sod→ each carbon is joined to 3 others in layered structure
○ Coordination no. = 3
● Nanoscience
○ Refers to the science of structures that are 1- 100nm in size
● Nanoparticles
○ Show different properties to the same materials in bulk and have a high surface area to
volume ratio
● Fullerenes
○ Although they are not officially classed as giant molecules, fullerenes are made from
carbon atoms joined together to make tubes and cages
● Nanotubes
○ They are fullerenes where hexagonal sheets of carbon atoms have rolled into a tube
● Properties of fullerenes
○ Very strong → useful where lightness and strength are needed (tennis racket frames)
○ Conductors of electricity → used as semiconductors, electrical circuits
○ Tubular structures → used to transport a drug into the body
● Buckminster fullerene
○ A fullerene where the carbon dioxide are arranged in a ball shaped molecule
○ C60 → 60 carbon atoms are arranged in a ball in rings of 5 and 6
● Silica
○ M.P → very high
○ Strength → strong → joined to 4 oxygen which are joined to 2 silicon
○ Electrical → non-conductor
● Metallic bonding
○ Layers slide over each other because of the sea of delocalised electrons and that makes
metals
○ Because of free electrons that are mobile, metals are able to conduct electricity
○ The forces between +/- are extremely strong thus have high melting and boiling points. A
lot of heat energy is needed to overcome the attraction
○ All electrons operate as a sea of delocated electrons ffc
Diamond
Graphite
Tetrahedral structure
Hexagonal structure
All electrons are bonded thus do not conduct
electricity
Only 3 electrons are bonded, can conduct
electricity
High mp/bp because there are a large no. of
molecules that require large amount of energy to
break their bonds
Mp/bp is same as diamonds as they are both giant
covalent molecules
Hard
Soft → the layers slide over each other as they
have weak Van Der Waals forces that are broken
hence used in pencils
Used as diamond cutters
Used as lubricants
Covalent molecules
Hydrogen chloride(HCl)
Water(H2O)
Ammonia(NH3)
Carbon Dioxide(CO2)
Ethene(C2H4)
