Metal atoms and hydrogen atoms lose electrons to form positive ions.
Non-metal ions gain electrons to form negative ions.
The number of charges on a positive ion is the same as the group number of the element.
The number of charges on a negative ion is 8 - the group number of the element.
Nobel gas structure-
Ions have the stable electronic structure of a Nobel gas ( element from group 0 ). Nobel gas atoms have 8 electrons in their outer shell except for helium which has only 2. These atoms have no tendency to lose or gain electrons.
Ionic compounds contain positive and negative ions, formed when atoms transfer electrons:
Group 1 elements ( The alkaline metals ):
They are metals.
React with non metal elements to form ionic compounds.
Produce ions with a 1+ charge.
Group 7 elements ( The halogens ):
Are non metals.
React with metal elements to form ionic compounds.
Produce ions with 1- charge.
Forming ionic compounds:
Group 1 elements react with group 7 elements to produce ionic compounds. For example sodium reacts with chlorine to form sodium chloride. This contains sodium ions.
Giant ionic structures
An ionic compound is a giant structure of ions.
The ions are held in a regular arrangement called a lattice.
Ionic bonds are strong electrostatic forces of attraction between oppositely charged ions. They act in all directions in the ionic lattice, holding the structure together.
Covalent bonds in simple molecules:
Covalent bonds form when atoms share electrons. It forms between two non-metal atoms.
Covalent bonds are strong.
Can be represented as H-H.
Hydrogen exists as simple molecules. A simple molecule contains only a few atoms joined together by covalent bonds.
Covalent bonds in macromolecules:
Macromolecules: Have giant covalent structures. Each molecule contains very many atoms joined together by covalent bonds.
Macromolecules can be:
Elements like diamond ( a form of carbon ).
Compounds like silica ( silicon dioxide ).
A diamond is a single molecule containing carbon atoms. Each carbon atom is covalently bonded to 4 other carbon atoms forming a giant covalent structure.
Sand contains silica. Each silicon atom is covalently bonded to four oxygen atoms and each oxygen atom is covalently bonded to two silicon atoms. This gives it the formula SIO2 , which is why it is also called silicon dioxide.
Properties of simple molecules
A simple molecule consists of just a few atoms joined together by covalent bonds.
Low melting and boiling points:
Substances that exist as simple molecules such as oxygen O2.
Have relatively low melting points and boiling points.
Tend to be gases or liquids at room temperature ( but can be solids such as wax ).
These are weak intermolecular forces between simple molecules.
The intermolecular forces are relatively easy to overcome or break.
The covalent bonds do not break.
Properties of macromolecules
Simple molecules and macromolecules both contain covalent bonds, but they have different properties:
Very high melting points.
Are solid at room temperature.
The atoms in macromolecules are joined together by strong covalent bonds to form a network of atoms called a giant covalent lattice.
Diamond: Each atom is bonded to 4 others.
Strong covalent bonds between atoms.
Graphite: The carbon atoms in the graphite form layers.
Each atom is bonded to 3 others.
Weak intermolecular forces between layers.
Strong covalent bonds between atoms in a layer.
Properties of ionic compounds:
The properties of ionic compounds such as sodium chloride and magnesium oxide, can be explained by their structure and bonding:
Melting and boiling points:
The diagram shows part of the ionic lattice of a crystal of sodium chloride.
Ionic compounds like sodium chloride have:
High melting points.
High boiling points.
Large amounts of energy are needed to break the many strong ionic bonds in ionic compounds. This is why ionic compounds are solid at room temperatures.
Metals consist of giant structures of atoms packed together in a regular pattern or lattice.
This explains some of their properties for example metals can be bent in to shape as the layers of atoms can slide over eachother.
Metalic bonds are stong.
Conduction in metals:
Delocalised electrons in metals are free to move through the structure.
This is why metals conduct heat and electricity.
An alloy is a metal mixed with one or more other elements. This fills in the gaps of atoms making it stronger.
Thermosoftening: For example polyethene, consist of individual polymer chains.
They soften and melt when heated. Intermolecular forces are weakened when the polymer is warmed, letting the chains slide over eachother easily.
Thermosetting: Consist of polymer chains with cross links between them. Thermosetting polymers do not soften or melr when heated.
LDPE- Low density polyethene.and HDPE- High density polyethene-
Made at a different temperature and pressures than HDPE.
Different catalysts are also used.
LDPE and HDPE have different uses because they have different uses
1-100nm in size - Very tiny.
Their small size means that they have:
A high surface area.
Properties different from the same subatance in larger pieces.
Uses of nanoparticles-
The special properties of nanoparticles may lead to the development of new...
Computers, catalysts, coatings (Self cleaning windows) , sensors, lighter but stronger construction materials and cosmetics such as deoderant and suncream.
One example of nanoparticles. They are made up of carbon and have a structure similar to a graphite layer rolled in to a tube. They are strong and conduct electricity. Used in tennis rackets and golf clubs.
Atoms and isotopes:
The MASS NUMBER: Total number of protons and neutrons.
The ATOMIC NUMBER: Total number of protons.
Number of neutrons: Mass number-atomic number.
Number of electrons: Atomic number.
Protons have a mass of 1 and a + charge.
Electrons have a very small mass and a - charge.
Neutrons have a mass of 1 and a neutral charge.
Isotopes- Atoms of the same element with the SAME number of protons and electrons but a DIFFERENT number of neutrons.
Relative formula mass:
The relative formula mass is all the relative atomic masses added up (Ar) - Mass numbers.
Mr symbol for relative formula mass.
O2 - 16+16 = 32
They are likely to be the same substances if they:
Are the same colour.
Travel the same distance up the paper.
- Draw a pencil line near to the bottom of the paper.
- Add spots of colouring to the line.
- Put the paper in to a tank with a lid but don't let the line touch the solvent.
- Take the paper out before the solvent reaches the top.
- Examine the spots.
It allows a mixture of compounds to be separated.
The output from gas chromotography is a gas chromatogram.
The retention time is the time taken for a substance to pass through the column to a detector.
The column separates the gas.
% By mass = Ar / Mr x100 -> Relative atomic mass / Relative formula mass x100
Moles = Mass / AR (Formula mass)
1: Convert to moles.
2: Divide each by the smallest number.
3: Work out the ratio (If it is a decimal, round it - If 1.5, double both numbers)
4: Put it back in to the formula : Fe2O3 for example.
Reacting mass calculations:
Mass of reactant / Total Mr of reactant (Formula mass) x Total Mr product
Actual mass / Predicted mass x 100
Product can by lost when:
Separated from the reaction mixture.
The reaction may be reversible.
Lost through heating and evaporation.
The reaction may react in differnt way to what was expected.
Rates of reaction:
The rate of a reaction can be found by measuring:
Rate = Amount of reactant used / Time
Rate = Amount of product formed / Time
Rates of reaction experiments:
Rates of reaction experiments:
Rates of reaction experiments:
Measure the time taken for the cross to disappear.
Rates of reaction experiments:
Measure the time taken for the Mg to disappear.
Changing rates of reaction:
Reactions will only take place when particles collide with enough energy.
Minimum energy = Activation energy.
Concentration increase -> Increases the number of successfull frequent collisions -> Increases the rate of reaction.
Temperature increase -> Increases the speed of particles -> Increases the number of successfull frequent collisions -> Increases the rate of reaction.
Pressure increase -> Increase in pressure -> Increases the number of successfull frequent collisions -> Increases the rate of reaction.
Surface area -> Increase in SA -> Increases the number of successfull frequent collisions -> Increases the rate of reaction.
Remain chemically unchanged.
Can be used in small amounts.
Can be toxic.
Sometimes expensive (Gold).
Exothermic: Heat is given out.
Endothermic: Energy is taken in from the surroundings.
One direction is endothermic, one is exothermic.
The same amount of energy is tansferred.
During electrolysis positive ions are attracted to the negative electrode and move to it.
Positive ions gain electrons and are REDUCED.
Negative ions go to the positive electrode.
Negative ions lose electrons and become OXIDISED.
Remember: OIL RIG
Loss of Electrons. Gain of electrons.
Manufacture of aluminium:
Electrolysis of aluminium oxide.
It is insoluble so it must be molten for its ions to move about. However it has a high melting point which makes the process expensive.
Cryolite is used to reduce temperatures and energy cost in the process: It has a lower melting point.
Oxygen forms at the electrodes.. Oxide ions more to positive electrodes lose electrons and form oxygen.
Aluminium ions move to negative electrodes, gain electrons and form alluminium.
Aluminium is poured off.
At the electrodes:
The negative electrode: Metal or hydrogen are given off and ions gain electrons.
The positive electrode: Non metal except hydrogen, ions lose electrons.