Year 8 Summary SheetTopics covered in year 8:

Atoms and ions Writing chemical formulae and balanced chemical equations Reactivity series and salts Elements, mixtures, compounds and states of matter Extraction of metals Metals – properties and bonding Limestone

Atoms and Ions

Atom is a neutral particle with equal number or protons and electrons

Ion is a charged particle with uneven number of protons and electrons. Ions can be either positive or negative

An atom becomes an ion by either losing or gaining electrons to achieve a full outer shell (providing extra stability)

Elements in groups 1-3 will lose electrons to gain full shell configuration forming positive ions

o Group 1 +1 ionso Group 2 +2 ionso Group 3 +3 ions

Elements in groups 5-7 will gain electrons to gain full shell configuration forming negative ions

o Group 5 -3 ionso Group 6 -2 ionso Group 7 -1 ions

Reactivity of group 1 and 2 metals in water

All elements in the same group will react in the same way as they have the same out shell configuration (same number of electrons in the outer shell)

Group 1 metals (Alkali metals) with water

Produce hydrogen gas on reaction – popping sound Produce alkaline solution once reacted – blue with universal indicator

Equations (Word and balanced chemical equation)

General equation: Metal + Water Metal hydroxide + Hydrogen

Example word equation: Lithium + Water Lithium hydroxide + Hydrogen

Example chemical equation: 2Li + 2H2O 2LiOH + H2

Group 2 (alkali earth metals) with water

Produce hydrogen gas on reaction – popping sound Produce alkaline solution once reacted – blue with universal indicator

Equations (Word and balanced chemical equation)

General equation: Metal + Water Metal hydroxide + Hydrogen

Example word equation: Calcium + Water Calcium hydroxide + Hydrogen

Example chemical equation: Ca + 2H2O Ca(OH)2 + H2

How reactive they are however will differ……for groups 1 and 2 the elements become more reactive as you go down the group. Why is this?

In order to react the atoms must form ions. How easily they form ions explains how reactive they are.

o Easier to form the ion = higher reactivity Formation of the ion links back to the atomic structure

Example: Potassium is more reactive than lithium

K larger atom (more full shells of electrons) Outer electron held further away from nucleus Outer electron feels less nuclear attraction (pull from the positive charge of the nucleus) Easier for outer electron to be lost…therefore reacts quicker

Writing chemical formulae and balanced chemical equations

Chemical formulae

When writing a chemical formula you need to know the charges on the ions that make up the compound, (see above for atoms and ions)

The charges on the ions within the compound must balance so that a neutral compound is formed

Some examples are shown in the table below

+ ion - ion formula

Li +

(+1 ion as in group 1 of PT)Cl –

(-1 ion as in group 7 of PT)LiCl

Opposite and equal charges so just one of each

Mg 2+

(+2 ion as in group 2 of PT)O 2-

(-2 ion as in group 6 of PT)MgO

Opposite and equal charges so just one of each

Li + O 2- Li2O2 Li + needed to make 2+ and

balance 2- charge on OMg 2+ Cl - MgCl2

2 Cl – needed to make 2- and balance the 2+ charge on Mg

Al 3+

(+3 ion as in group 3 of PT)O2- Al2O3

Both ions multiplied up to form +6 and -6

Mg 2+ N 3-

(-3 ion as in group 5 of PT)Mg3N2

Both ions multiplied up to form +6 and -6

If the ion that is present in the compound is not a simple element but a complex ion such as NO3-

(nitrate), SO42- (sulphate) or NH4

- (ammonium) then bracket may be needed in the formula.

Examples are shown in the table below

+ ion - ion formula

NH4 + Cl - NH4Cl

NH4 + O2- (NH4)2OLi + NO3 - LiNO3

Mg 2+ NO3 - Mg(NO3)2

The complex ions are treated in the same way as the simple element ion but all the elements within the complex ion must be kept together which is why the brackets are needed.

(NH4)2O: within this compound there are 2 ammonium (NH4) ions and 1 oxygen (O) ion

Without the brackets NH42O: There would now appear to be 1 Nitrogen, 42 Hydrogen and 1 oxygen!

Cross over method

The cross over method can be used to help with the writing of chemical formula. In this method the charge of the opposite ion gives you the number of the element in your formula

Li +O2-

Li2O

Mg 2+ O2-

Mg2O2

Writing balanced chemical equations

When balancing a chemical equation you need to count up the number of atoms of each element on either side to ensure they are all balanced

Atoms cannot be created or destroyed just rearranged!

Look at the following chemical equation

Mg + HCl MgCl2 + H2

Number of atoms on LHS: 1 Mg, 1 H, 1 Cl Number of atoms on RHS: 1 Mg, 2 H, 2 Cl

To balance a chemical equation only BIG numbers IN FRONT of products or reactants can bee added

Mg + 2HCl MgCl2 + H2

Number of atoms on LHS: 1 Mg, 2 H, 2 Cl Number of atoms on RHS: 1 Mg, 2 H, 2 Cl

This formula would be simplified down to just one of each MgO

Equation is UNBALANCED

Equation is BALANCED

Mg 2+Cl-

MgCl2

Reactivity series and salts

The reactivity series of metals is shown below, along with a mnemonic to help you to remember the order. Carbon and hydrogen are not metals but are included to help with understanding some of the reactions of metals

The following link is for a song to help remember the reactivity series if you prefer this to the mnemonic : https://www.youtube.com/watch?v=DLlykUHHAcQ

Metals and acid

The reaction of a metal with an acid will be the same in all cases (if it reacts). How vigorously the metal reacts with the acid depends on its position in the reactivity series.

Common acids

Hydrochloric acid: HCl Sulphuric acid: H2SO4

Nitric acid : HNO3

Observations:

Fizzing (as a gas is produced) Metal will disappear as it reacts

General reaction: Metal + Acid Salt + Hydrogen

MASH: Metal Acid Salt Hydrogen

All acids contain the element hydrogen.

This is why Hydrogen is included in the reactivity series

The reactions of the metal with an acid depends on its position in relation to Hydrogen

If you compare the reactivity of two metals in the same acid a metal higher in the reactivity series will react more quickly. More rapid bubbles will be observed and the metal will disappear more quickly.

The metal will ONLY REACT if it is higher in the reactivity series than hydrogen so Copper, Silver and Gold will not react with acid. You will observe nothing if acid is added to these metals

Test for Hydrogen

How do we know that hydrogen gas is made? We can test for it

Lit splint will produce a squeaky ‘pop’ sound in hydrogen gas

Naming salts

The name of the salt is made up of two parts

The first part of the name is simply the metal The second part is dependent on the acid it reacts with

Acid Name of salt Formula for ion in the saltHydrochloric acid Chloride Cl-

Sulphuric acid Sulphate SO4 2-

Nitric acid Nitrate NO3 -

Example reactions

Magnesium + Hydrochloric acid Magnesium Chloride + Hydrogen Mg + HCl MgCl2 + H2

Zinc + Sulphuric acid Zinc Sulphate + Hydrogen Zn + H2SO4 ZnSO4 + H2

Lead + Nitric acid Lead nitrate + Hydrogen Pb + HNO3 Pb(NO3)2 + H2

Displacement reactions

A displacement reaction involves a metal and a compound of a different metal. The more reactive metal will displace the less reactive metal

This reaction will only occur if the metal added is more reactive than the metal in the compound. It needs to be ‘strong’ enough to steal away the negative ion from the other metal

To identify if a displacement reaction will occur you will therefore need to refer again to the reactivity series.

If a displacement reaction does happen then you will observe

The more reactive metal disappearing The less reactive metal coating the surface of any metal still present or sinking to the bottom

of the reaction vessel

Example reactions

Copper sulphate + Magnesium Magnesium Sulphate + Copper

CuSO4 + Mg MgSO4 + Cu

Observations: Blue copper sulphate colour fading

Magnesium disappearing

Copper solid appearing

Other examples

Lead nitrate + Aluminium Aluminium nitrate + Lead

3Pb(NO3)2 + 2 Al 2Al(NO3)3 + 3Pb

Zinc Chloride + Calcium Calcium chloride + Zinc

ZnCl2 + Ca CaCl2 + Zn

Potassium Chloride + Sodium NO REACTION

This reaction will NOT occur because Sodium is lower in the reactivity series than potassium and therefore is no strong enough to ‘steal’ the chloride ion away from the potassium

Elements, mixtures, Compounds and States of Matter

Changes of state

The three states of matter are solid, liquid and gas. You need to be able to draw the particle diagrams for each and describe the properties and arrangements of the particles

Solid Liquid Gas

State Arrangement of particles

Attractive forces between particles

Kinetic (movement) energy

Solid Regular arrangement, particles close

together

Attractive forces between particles

close together

No kinetic energy (particles just vibrate)

Liquid Less regular arrangement, particles

still close together

Some forces of attraction between

particles

Some kinetic energy, particles flow over

each otherGas No arrangement No forces Lots of kinetic energy,

particles move in all directions

Changes of state

Solid Liquid : Melting Liquid Gas : Evaporating Gas Liquid : Condensing Liquid Solid : Freezing Solid Gas : Subliming

Heating and cooling curves: This shows the change in temperature over time as a substance is heated.

Why are the sections of the graph flat when the substance is changing state?

During melting and evaporating, internal energy increases as the motion of the particles increases and bonds are broken

During condensing and freezing the internal energy decreases and the motion of

particles decreases and new bonds are formed

Elements, mixtures and compounds

Definitions

Element: A substance that cannot be broken down into any other substance. Examples show Carbon, Copper and helium

Compound

Substance made from different atoms joined

together

Element

Substance made form only one type of atom

Mixture

Contains different particles

Pure Substance

all particles are the same

Substance

Mixture: A substance that contains two or more elements or compounds that are NOT chemically bonded. Example shows hydrogen and oxygen gas mixed together

Compound: A substance the contains two or more elements that ARE chemically bonded. Example shows water

Molecule: A substance that contains two or more atoms chemically bonded together. These can be atoms of he same element (diatomic molecule) or different elements (compound). Examples show diatomic molecule of oxygen and molecule of the compound water

Atom: Smallest particle of a chemical element that can exist

A B C

D

Atoms of element Molecule of elementMixture of elements

F

Molecule of compound Mixture of compoundMixture of compounds and

elements

AAAAAAAAAAAAAAAAA BBBBBBBBBBBBBBBBB CCCCCCCCCCCCCCCCC

DDDDDDDDDDDDDDDDD FFFFFFFFFFFFFFFFF

Extraction of metals

Most metals are found within the earth’s crust combined with other elements in rocks known as ores. These metals need to be extracted from their ore in order to be turned into useful products. Mining for ores is expensive so this will only be carried out it the rock contains sufficient metal to make the work profitable.

There are two methods of extracting metal from its ore. The choice of process is dependent on the reactivity of the metal.

Reduction with carbon: The cheaper of the two methods but can only be used with metals lower than carbon in the reactivity series (see back in notes for reactivity series)

Most metals are combined with oxygen in their ore; this oxygen must be removed for the metal to be extracted. The removal of oxygen is known as REDUCTION

Heating a metal ore that is less reactive than carbon with carbon will lead to the oxygen bonding to the carbon rather than staying bonded to the metal

Copper oxide + Carbon Copper + Carbon dioxide

Electrolysis: This is a more expensive method of metal extraction so is only used to extract metals more reactive than carbon where other method will not work

Electrolysis is the process of using electricity to separate the elements in a compound. The word electrolysis means ‘splitting with electricity’

Anode: Positive electrode

Cathode: Negative electrode

Electrolyte: Liquid or gel which contains ions and can be decomposed by electrolysis

Anions: negative ions which are attracted to the positive electrode

Cations: positive ions which are attracted to the negative electrode

Example: Extraction of copper from copper chloride

Electrolyte – Copper chloride. In solution this forms Cu2+ ions and Cl- ionso Anion – chloride ions (Cl-) Cation – copper ions (Cu2+)

What happens at each of the electrode?

Anode: 2Cl - Cl2 + 2e-

The extra electrons that the chloride ions contain are given up when they reach the anode. These electrons then travel through the electrical circuit to the cathode (completing the electrical circuit)

Cathode: Cu2+ + 2e- Cu

The electron supply at the negative cathode are picked up by the copper ion turning back to neutral copper atoms

The oxidation and reduction of the elements in an electrolysis reaction is described in terms of loss and gain of electrons

OILRIG

Oxidation Is Loss, Reduction Is Gain

Chloride ion has been oxidised to form chlorine gas

Copper ion has been reduced to form Copper

Metals – properties and bonding

The diagram below shows the bonding in a metal.

It is made up of a regular arrangement of metal ions (formed when the metal atoms lose electrons to gain a full outer shell). Every atom of an element in group 1 will donate 1 electron to the delocalised sea but atoms of a element in group 3 will donate 3

o These electrons make up the sea of delocalised electrons which act as a glue holding the ions together.

The delocalised electrons are free to move; they are not attached to the metal ions. The metal ions are not bonded together but able to slide over one another

Properties of metals

The properties of a metal are linked to the bonding. The three main points made about the bonding above can be used to explain the different properties we see

Good conductors of electricity – the sea of delocalised electrons is able to carry the electric current through the metal. The larger the sea of electrons the better it will conduct.

Malleable (to bend into shape) and ductile (to pull into wires) – as the metal ions are able to slide over each other it is easy to change the shape of the metal or pull it out into a wire. The delocalised electrons move with the ions holding the ions in whatever shape it has been made into

High melting point and boiling point – for the metal to melt the electrostatic attraction between the ions and electrons must be overcome. This is a strong attraction and therefore requires a lot of energy to occur. The higher the charge on the ion (and larger the electron sea) the greater the electrostatic force and the higher the melting point

Limestone

Limestone cycle

The limestone cycle involves the following compounds

Calcium carbonate: CaCO3

Calcium hydroxide: Ca(OH)2

Calcium oxide: CaO

Reactions – word and chemical equations

Calcium carbonate Calcium oxide + Carbon dioxide

CaCO3 (s) CaO (s) + CO2 (g)

This is a thermal decomposition reaction. By heating the calcium carbonate strongly the calcium carbonate will break down into two new products (calcium oxide and carbon dioxide)

Calcium oxide + water Calcium hydroxide

CaO (s) + H2O (l) Ca(OH)2 (s)

The initial addition of a small amount of water changes the calcium oxide into solid calcium hydroxide.

Ca(OH)2 (s) + H2O (l) Ca(OH)2 (aq)

Addition of more water will dissolve the solid calcium hydroxide into a solution of calcium hydroxide also known as limewater

Calcium hydroxide + Carbon dioxide Calcium carbonate

Ca(OH)2 (aq) + CO2 (g) CaCO3 (s)

This is the test for carbon dioxide. The solid calcium carbonate that forms makes the limewater look cloudy

Reaction with acid

Observations when a carbonate reacts with acid

a) Bubbling / fizzing / effervescenceb) Solid carbonate gets smaller c) When tested the gas turns limewater cloudyd) Heat is produced during the experiment

Inferences from the observations

a) A gas has been formedb) The solid is reacting to form new products in solutionc) The gas that has formed is carbon dioxided) The reaction is exothermic

Example reaction

Calcium carbonate + Hydrochloric acid Calcium chloride + Carbon dioxide + Water

CaCO3 + 2HCl CaCl2 + CO2 + H2O

The products of a carbonate and acid reaction will always be the same with the exception of the salt that is made. This is depend on the metal in the carbonate and the acid used

Other examples

Barium carbonate + Nitric acid Barium nitrate + Carbon dioxide + Water

BaCO3 + 2HNO3 Ba(NO3)2 + CO2 + H2O

Zinc carbonate + Sulphuric acid Zinc sulphate + Carbon dioxide + Water

ZnCO3 + H2SO4 ZnSO4 + CO2 + H2O