Chemistry Revision

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GCSE Science (Chemistry) Note on Chemistry Revision, created by lisharding on 01/06/2014.
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Atomic Structure And The Periodic Table

Electrons - Negative Charge - Atomic Mass 0Protons - Positive Charge - Atomic Mass +1Neutrons - No Charge - Atomic Mass +1

Elctrons

Nucleas

Protons

Neutrons

     24Mg     12

       Atomic mass(Protons And Neutrons)

   Atomic Number(Number of Protons)= Number of Elctrons

The symbol for relative Atomic Mass is Ar

Looking At Chlorine

   35.5Cl   17

Cl - 35 = 75%Cl - 37 = 25%

Relative Atomic Mass

%  x  Ar        % x Ar(75 x 35)  +  (25 x 37)         75  +   25

Ionic Bonding

Salt = Sodium and Chlorine            (Na)             (Cl)

Sodium give Chlorine an Electron

(Cation)

(Anion)

A

An Ion is an atom or group of atoms with a positive or negative charge, because they have gained or lost electrons.

I

Ionic Compunds

Al2 O3 -Aluminium Oxide                 Al3+      O2-

Al3+                    O2-Al3+                    O2-Al3+                    O2-

Al2                             O3

Compound Ions contains more than one element. For example, the nitrate ion, NO3- contains one nitrogen atom joined to three oxygen atoms and an extra electron. If two or more compound ions of the same type are needed in a formula, the ions of the same type are needed in a formula, the ion must be written inside brackets. For Example, the formula of Magnesium Nitrate is Mg(NO3)2. This shows that the two positive charges in one Mg2 ion are balanced by two negative charges from two NO3 ions.

Ionic Substances

Solid -Doesn't conduct electricityMolten Liquid - Does Conduct electricityDissolved in Water - Does conduct electricity

2 Conditions for Electrolysis:It must contain charged particlesMust be free to move

Simple Molecular Covalent Substances

Low Melting PointsLow Boiling pointsPoor Conductors of Electricity

Includes gases, such as hydrogen and oxygenWeak Bonds

Giant Molecular Covalent Substances

Billions of atoms joined togetherHigh Melting PointHigh Boiling Point

Strong bondsGiant Molecular StructureConduct Electricity

Halogens

The 

The halogens or halogen elements are a group in the periodic table. Consisting of five chemically related elements - Fluorine, chlorine, iodine, bromine and astatine.

Chlorine's Reaction With MetalsChlorine combines directly with all metals forming metal chloride salts.

Bromine's Reaction With MetalsBromine reacts vigorously with metals, especially in the presence of water, to give Bromide Salts.

Iodine's Reaction With MetalsWhen A small quantity of powdered aluminium is mixed with some iodine crystals and a few drops of water are added, a reaction happens, producing purple iodine vapor and flame. Aluminium iodine is the product.

Metallic Bonding

The useful properties of metals include malleability and the ability to conduct electricity

Transition Metals

Are found in the middle of the periodic tableAre all solids at room temperature (Except Mercury)Are usually malleableExamples are iron, silver and titaniumUsually have high melting points

Are usually good conductors of electricityUsually ductileUsually denseHave lots of usesAre usually strong

Noble Gases

The Noble gases are in group 0 of the periodic tableIt is difficult to make them react with anythingAll have full outer electron shellsXenon and Argon were formerly used inside filament lampsArgon and Helium are used in weldingArgon is used in fire-extinguishersHelium had a low density and so is used in balloons and airshipsNeon is used in florescent lamps and advertising displays

Exothermic and Endothermic Reactions

When a chemical reaction takes place there is often an energy transfer between the reactants and the surroundings. If the energy transfer is in the from of heat energy then there is a change in temperature.

Exothermic changes give out heat energy. Most chemical reactions are exothermic the head energy given out causes the temperature of the reaction mixture and its surroundings to increase.

Endothermic changes take in heat energy from the surroundings, so the temperature of the surroundings decreases. Not many chemical reactions are endothermic.

Catalysts

Catalysts are used to speed up a reaction to increase the rate at which a product is made or to make a process cheaper. They are not normally used up in a reaction.

Quantitative Chemistry

Relative Formula Mass (Mr)The Relative formula mass of a compound is the relative atomic masses of all the elements in the compound added together.

Empirical FormulaEmpirical Formula is simply a way of showing how many atoms are in a molecule.

A

A Classic EXAM Question - Find the simplest formula of 2.24g of iron reacting with 0.96g of oxygen

Step 1 - Divide both masses by their relative atomic massIron        2.24/56 = 0.04Oxygen  0.96/16 = 0.06

S

Step 2 - Write this as a ratio and simplify0.04 : 0.06 is equivalent to 2:3

Step 3 - Write the formula2 iron atoms for 3 oxygen atoms means the formula is Fe2O3

Calculating Percentage Mass 

Practice EXAM Question - Calculate the percentage mass of magnesium in magnesium Oxide (MgO)

Ar for Magnesium = 24Ar for Oxygen      = 16Mr for Magnesium Oxide = 24 + 16 =40Percentage Mass = 24/40 x 100 = 60% of Magnesium Oxide is Magnesium

Calculating the Mass of a Product

Step 1 - Read the equation 2mg + O2  ----> 2MgO

Step 2 - Work out the relative formula masses2Mg + O2 ----> 2MgO48   + 32 ----> 80

Step 3 - Learn and Apply the following three points1) 48kg of Mg makes 80g of MgO2) 1g of Mg makes 80/48 = 1.66g of MgO3) 60g of Mg makes 1.66 x 60 = 100g of MgO

Percentage Yield

Theoretical Yield - The amount of product that should be made as calculated from the masses of atoms.

Actual Yield - What was actually produced in the reaction

Percentage Yield = Actual Yield (in grams)                                Theoretical Yield

Practice EXAM Question - 65g of Zinc reacts with 73g of hydrochloric acid and produces 102g of Zinc Chloride. What is the percentage yield?

Zn + 2HCl ----> ZnCl2 + H2102/138 = 73.9%

Subatomic Particles

Atoms are made from three types of subatomic particle. The Nucleus Contains protons and Neutrons. Subatomic particles have very, very small masses and electrical charges.

Atoms and Elements

Every atom of a particular element has the same number of protons. No two elements have the same number of protons, all atoms contain the same number of protons as electrons.

Isotopes

Isotopes are different atoms of an element with the same number of protons and electrons but different numbers of neutrons.

Electron Shells

Electrons are arranged in shells around the nucleus of the atom.Different shells can contain different numbers of electrons. The first shell can hold up to two electrons, the second and third shells can hold up to 8 electrons.

Spotting Connections

There are several connections between an elements electronic configuration and where it is found in the periodic table. The number of occupied shells is the same as the period number, apart from the elements in group 0, which all have full outer shells, the number of outer electrons is the same as the group number.

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