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Isotopes,elements and compounds

Definition of an isotope: Different atomic forms of the same element which have the samenumber of protons but different number of neutrons ̂Basically they have the same atomic number but different

mass number

Elements are made of only 1 type of atom -They can't be broken down easily

Compounds are chemically bonded-after the chemical reaction it's hard to separate elementsagain -Properties of compound are different to the properties of the elements it was made from.

There are 2 types of chemical bonding: -Ionic bonding -Covalent bonding

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Atoms

Nucleus -Contains protons and neutrons -Positive charge

Electrons -Negative charge -They are in shells around the nucleus

Mass Charge

Proton 1 +1 Neutron 1 0 Electron 0.0005 -1

• Number of protons=Number of electrons• Number of neutrons= Atomic number-Mass number• Mass number is the top number of the element• Atomic number is the bottom number of the element

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Ionic Bonding

In ionic bonding atoms lose or gain electrons to form ions which are strongly attracted to eachother Atoms in group 1 and 2:-Have 1/2 electrons in their outer shell -get rid of extra electron/sby giving them to an atom with the opposite charge -Now they are both ions with full outer shells Atoms ingroup 7 and 8:-Have 7/8 electrons in their outer shell -They gain electrons from other atoms ofthe opposite charge to fill their outer shell -Now they are both ions with full outer shells

•Ions are charged particles•Full outer shells are called stable octets•When metals form ions they lose electrons to form positive ions•When non-metals form ions they gain electrons to form negative ions•OILRIG (oxidation is gain , reduction is loss) <of electrons•When a metal and a non metal combine they form ionic bonds

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The periodic table

Vertical columns are called groups -Number of electrons an element has in its outer shelldetermines its group -Elements in the same group have the same number of electrons in theirouter shells -Elements in the same group have similar properties

Rows are called periods -Each period represents another full shell of electrons -Number of shellsan element has determines its period

Electron configuration

The maximum number of electrons in each shell is: 1st shell : 2 2nd shell: 8 3rd shell: 8

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Alkali metals

•Alkali metals are all the metals in group 1•These are : Lithium,Sodium,Potassium,Rubidium,Caesium and Francium•As you go down group 1 the alkali metals get more reactive because the electron in the

outer shell is more easily lost because its further from the nucleus•They all have 1 outer electron

They all have similar properties: -Low melting and boiling points -Low density -Very soft -All veryreactive -Always form ionic compounds in an oxidation reaction

They react with cold water to make hydrogen gas -Li,Na,K react vigourously -they move aroundthe surface and fizz -Sodium and Potassium melt in the reaction -They form a hydroxide

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Ions and ionic compounds

NaCl and MgO form giant lattices -Ionic bonds always produce giant ionic structures -The ionsaren't free to move so when solid they don't conduct electricity -Very strong bonds between all ions

• They have high melting and boiling points due to strong chemical bonds• They conduct electricity when molten because the ions are free to move when in molten

form so they can carry a current• NaCl dissolves to form a solution that conducts electricity

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Electrolysis

Definition: Electrolysis is the breaking down of a substance using electricity -It needs aliquid -the electrolyte- to conduct the electricity -Electrolytes are usually free ions dissolved in waterwhich are the things that conduct electricity

•In electrolysis electrons are taken away from ions at the positive anode and given to otherions at the negative cathode

Electrolysis of sulfuric acid:-Water contains Hydrogen and water -Water isn't a good conductorso if you dissolve sulfuric acid in ,it conducts electricty better

•Oxygen is produced at the anode•Hydrogen is produced at the cathode

Negative ions are called anions, positive ions are callled cations

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Alkali metals continued

Example of reaction with water: 2Na+ 2H#O ===> 2NaOH + H#

Alkali metals burn with colours: Lithium=Red Flame Sodium=Yellow/orange flamePotassium=Lilac flame

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Extracting Aluminium

•Electrolysis removes aluminium form its ore•Pure aluminium oxide (Al#O#) is found in Bauxite•Aluminium is more reactive than Carbon so it is extracted from its ore using electrolysis•-Al#O# has a very high melting point of 2000#C•This temperature is hard and expensive to maintain•The solution is to dissolve it in Cryolite•This brings the melting point down to about 900#C which is easier and cheaper•The electrodes are made from graphite -a good conductor of electricity•Molten aluminium oxide contains free ions so it conducts electricity•

Positive ions are attracted to the Cathode where they pick up electrons and turn intoaluminium atoms and sink

•Negative O2# ions are attracted to the anode where they lose electrons -The oxygen atomsreact together to form O# or with carbon dioxide to form CO#

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Electrolysis continued

• At the cathode , 2 Hydrogen ions accept 2 electrons to become 1 Hydrogen molecule• At the anode , 4 Hydroxide ions lose their electrons and become 1 oxygen molecule and

2 water molecules

Learn these off by heart:

Cathode 2H# + 2e# ====> H# Anode 4OH# ====>2H#O + O# + 4e#

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Covalent Bonding

Covalent bonding is when atoms share electrons with each other-After covalent bonding theyboth have a full outer shell -Each covalent bond provides one extra shared electron for each atom

•Usually have simple molecular structures•Very strong covalent bonds in atoms•Forces of attraction between molecules are weak•Low melting and boiling points because of a weak intermolecular force•Most molecular substances are gases or liquids at room temperature•Molecular substances don't conduct electricity because there are no free electrons

or ions

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Extracting Aluminium continued

• As the Carbon anode is constantly being worn down it often needs replacing• It's a redox reaction because reduction and oxidation are happening at the same time

At the cathode + 3e# =====> Al (Reduction)

At the anode: 2O2# ======>O₂ + 4e₂ (Oxidation)

-Decomposition of aluminium oxide= Aluminium oxide =====> Aluminium+Oxygen

• Electrolysis uses a lot of electricity,lots of energy is needed and the cathode needs to bereplaced frequently so it is an expensive process

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Halogens continued

Halogens react with alkali metals to form salts

2Na + 2Cl# ====> 2NaCl 2K + 2Br# ======> 3KBr#

More reactive halogens displace less reactive ones

Cl# + 2KI ====> I# + 2KCl Cl# + 2KBr ====> Br# + 2KCl

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Halogens

• Group 7 elements are the Halogens• Fluorine,Chlorine,Bromine,Iodine and Astatine• All have 7 electrons in their outer shell• As you go down group 7 the halogens become less reactive because there's less

inclination to gain the extra electron to fill the outer shell because it's further away fromthe nucleus

-Chlorine is a poisonous dense green gas -Bromine is a poisonous dense orange liquid -Iodineis a dark grey crystalline solid

• Halogens form covalent bonds with themselves• They form ionic bonds with other elements like the alkali metals to form ions with a negative

one charge• RIG reduction is gain

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Superconductors

•If you make metals cold enough their resistance disappears, the metal is now called asuperconductor -Without any resistance none of the electrical energy is turned to heat sonone is wasted

•With superconductors you can make: >Power cables that transmit electricity without lossof power >Really strong electromagnets that don't need a constant power source >Reallyfast electronic circuits because there's no resistance to slow it down

•However metals only start superconducting at -265®c (expensive to do)•Scientists are trying to develop room temperature superconductors but so far only got to

-135®c

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Metals

• Metals consist of a giant structure of atoms held together with metallic bonds• These bonds allow the outer electrons of each atom to move freely Properties of metals:• High melting and boiling points• High density• Shiny• Strong attractions between the free electrons• Strong metallic bonding• High tensile strength• Malleable• Good conductors of heat and electricity

Stainless steel-saucepans-Good conductor of heat Copper-Electrical wiring-Good conductorof electricty,easily bent Aluminium-Aeroplanes-Low density,Strong,Doesn't corrode Steel/Iron-Bridges-Strong

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Thermal decomposition

Definition: When a substance breaks down into at least 2 other substances by heat

Transition metal carbonates break down when heated then they break down into a metal oxideand carbon dioxide:

CuCO# ====> CuO + CO# These reactions usually result in a colour change

(If limewater goes milky then there's Carbon dioxide present)

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Transition metals

They are found in the middle section of the periodic table

• They make good catalysts: 1) Iron is the catalyst used in Haber process for makingammonia 2)Nickel is used for the hydrogenation of alkenes

They have colourful compounds:

• Iron II compounds are light green• Iron III compounds are orange• Copper compounds are blue

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Precipitation

Definition:A percipitation reaction is where 2 solutions react and an insoluble solid forms in the solid

CuSO# + 2NaOH ===> Cu(OH)# + Na#SO#

Or this can be written as an ionic equation

Cu2⁺ + 2OH⁻ ====> Cu(OH)₂

•Copper Hydroxide is a blue solid•Iron II Hydroxide is a dark grey solid•Iron III Hyrdoxide is an orange solid