1i) Electrolysis

An electric current is the flow of electrons or ions. Covalent compounds can not conduct electricity because they make bonds by sharing electrons which means that they don't have any charge carriers that are free to move.

Electrolytes are liquids that conduct electricity:

Telling the difference between electrolytes and non-electrolytes:

When you place a conductivity probe in an electrolyte, the current flows through the circuit so you can measure its conductivity. When you place a conductivity probe in a non-electrolyte, no currents flow so the reading would be zero conductivity.

Another way of determining would be setting up an electrolytic cell, if the substance will undergo electrolysis then it is an electrolyte.

Electrolysis is when an electric current is passed through an ionic substance that's molten or in solution and it breaks down into a new substance(s). It is free electrons which conduct the electricity.

Example of Electrolysis is Molten Lead (II)Bromide or PbBr₂

Ion present: Pb²⁺ and Br^-

Ion attraction to electrode:

Cathode (-) Pb²⁺

Anode (+) Br^-

Half Equations of the electrodes show what is happening at each stage:

Cathode: Pb²⁺ + 2e^- → Pb

Anode: 2Br- → Br₂ + 2e^-

Electrolysis of aqueous solutions:

As well as the ions from the ionic compound there will be hydrogen ion (H+) and hydroxide ion (OH-) from the water

At the Cathode H+ ions or metal ions (if the metal is less reactive than hydrogen) are present

At the Anode OH- ions or a halide ion when they are in the experiment are present.

Examples:

Sulfuric Acid-

Contains three ions: SO₄^2-, H+ and OH-

Cathode (-) Hydrogen gas is produced:

half equation is 2H+ + 2e^- → H₂

Anode (+) Oxygen and water is produced:

half equation is 4OH- → 2H2O + 4e-

Copper (II) Sulfate-

Contains three ions: Cu²⁺, SO₄^2-, H+ and OH-

Cathode (-) Copper metal is produced:

half equation is Cu²⁺ +2e^- → Cu

Anode (+) Oxygen and water is produced:

half equation is 4OH^- → 2H₂O + 4e^-

Coulombs and Faradays are amounts of electricity:

• one amp flowing for a second means a charge of one coloumb has moved
• Q (charge) = I (Current) x t (Time)
• 96000 coulombs is called one faraday
• One faraday (F) contains one mole of electrons

1h) Metallic Crystals

Metals

• Have a giant structure of positive ions surrounded by free electrons
• Are held together by metallic bonding. They have a giant structure of positive ions surrounded by a sea of de-localised (free) electrons
• The attraction between the positive ions and electrons is called 'metallic bonding'
  It is the metallic bonding which gives metals their properties

Properties 

• hammered/ bent into shape 
• good conductors of heat and electricity due to the free electrons which carry the electrical  
• strong 
• malleable- atoms in a regular pattern in layers slide over eachother and can be hammered into shape

1e) Chemical Formulae and Chemical Equations

Word equations and Balanced chemical equations are used to represent the reactions studied in this specification. In a chemical equation you have to use state symbols: (s), (l), (g) and (aq) in chemical equations to represent solids, liquids, gases and aqueous solutions

Water of Crystallisation:

• solid salt with water is HYDRATED
• salt without water is ANHYDROUS
• calculate it by:

1. Working out the mass
2. Number of moles of water lost
3. ratio of anhydrous salt made
4. ratio of anhydrous to mole of Water
5. X must be a whole number

Empirical formula:

Is the simplest formula that tells you the ratio of different elements in the compound

1. List all the elements in the compound
2. Write underneath the experimental masses/ percentage
3. Divide by A_r of elements
4. Change to simple ratio by multiplying and/or dividing them by well chosen numbers
5. Simplify ratio

Molecular Formula:

A compound tells you the actual number of atoms each element in a single molecule

Calculate Masses in Reactions:

1. Write out the balanced equation
2. Work out the and multiply them by balancing numbers in the equation
3. Apply the rule: Divide to get one, then multiply to get all

Percentage Yield:

= (mass obtained/ mass predicted) x 100

Moles and Concentration

Concentration = Number of Moles / Volume

1d) Relative formula masses and molar of gases

Relative formula mass can be found by adding up the mass numbers

A mole is a precise number. When you get precisely that number of atoms or molecules, of any element or compound, they weight exactly the same number of grams as the relative atomic mass, A_r of the element or compound. One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance.

Example- Carbon has an A_r of 12 and so the one mole of carbon weighs exactly 12g.

The number 6.023x10²³ is called Avogadro's number or the Avogardo constant. So you can think of a mole as the Avogardo number of particles in a substance, where the articles are atoms, molecules, ions or electrons.

Number of moles = Mass in g/ M_r

One mole of any gas always occupies 24dmº (=24000 cmº) at room temperature and pressure (RTP: 25ºc and 1 atmosphere)

Volume (dm³) = moles of gas x 24

Volume (dm³) = (mass of gas/ M_r of gas) x 24

1f) Ionic compounds + 1g) covalent compounds

Ionic bonding:

• strong electrostatic attraction 
• opposite charged ions 
• throughout lattice 

Properties of ionic compounds:

• high melting point 
• strong electrostatic attraction 
• giant ionic lattice 
• soluble in water 
• Ions attracted to polar water molecules 
• conduct electricity 
• ions can move and carry charge

A Lattice is a 3-D network of ions in fixed positions bonded together 

OIL RIG 

Oxidation- loses electrons                      Reduction- gains electrons 

Group	1	2	3	4	5	6	7	0/8
Charge	1+	2+	3+	X	3-	2-	1-	X

Covalent bonding:

• non metal with non metal 
• outer shells overlap 
• electron shared in pairs 
• atoms achieve outer shells (full)
• attracts both nuclei 

Properties of simple covalent molecules:

• very strong bonds
• low melting and boiling points 
• insoluble in water 
• no free electrons 
• Don't conduct electricity 
• soluble in organ solvents 

Intermolecular forces 

• weak bonds
• easily broken 

Giant covalent bonds 

• strong bonds 
• no free electrons 
• rigid 
• all atoms joined together 
• covalent unreactive 

Diamonds 

• rigid 
• hard 
• sparkly
• four covalent bonds  

Graphite

• layers three covalent bonds 
• slide over each other 
• free electrons 
• good conductor of electricity 
• lubricant 

1c) Atomic structure

Nucleus- contains neutrons and protons
Protons- has a positive charge due to neutrons
Electrons- move around the nucleus in shells; negatively charged
2,8,8,2: Elements in the same group have the same number of outer shell electrons

Atoms consist of a nucleus in the centre, which has neutrons and protons. Protons have a positive charge due to neutrons. There are also electrons which move around the nucleus in shells and are negatively charged. Elements in the same group have the same amount of outer shell electrons.

Particle	Relative Mass	Relative Charge
Proton	1	+1
Neutron	1	0
Electron	1/2000	-1

• Atomic Number tells you how many protons there are
• Mass number is the total number of protons and neutrons in an atom
• Isotopes have the same chemical reactivity but different number of neutrons they also have the same molecular formula but different structural formula.
• The Relative atomic mass (Ar) is the average mass of all the isotopes of an element. It allows for the relative mass of each isotope and its relative abundance.
• Relative Abundance is how much there is of each isotope compared to the total amount of the element in the world. This can be represented as a ratio, fraction or percentage.

The Periodic Table

Is an arrangement of elements in order of their atomic number

Electronic configurations of the 1^st twenty elements

Element	Electronic Configuration
Hydrogen	1
Helium	2
Lithium	2,1
Berylium	2,2
Boron	2,3
Carbon	2,4
Nitrogen	2,5
Oxygen	2,6
Fluorine	2,7
Neon	2,8
Sodium	2,8,1
Magnesium	2,8,2
Aluminium	2,8,3
Silicon	2,8,4
Phosphorus	2,8,5
Sulphur	2,8,6
Chlorine	2,8,7
Argon	2,8,8
Potassium	2,8,8,1
Calcium	2,8,8,2

1b) Atoms

Diffusion is the gradual movement of particles from a high concentration to a lower concentration.

Dilution of coloured solution:

example- Potassium Manganate(VII) and Water:

1. Take a beaker of water and place some potassium manganate(VII) at the bottom, the purple colour will slowly spread out to fill the beaker
2. The particles of the potassium manganate(VII) are diffusing out among the particles of water
3. This is evidence of random motion of particles in a liquid that causes the purple colour to eventually be evenly spread out throughout the water

Diffusion Experiments:

Ammonia and Hydrogen Chlorine-

1. Aqueous ammonia gives off ammonia gas and hydrochloric acid gives off hydrogen chloride gas
2. When you set up the experiment a white ring will form of ammonium chloride in the glass tube
3. The NH3 gas diffuses from one end of the tube and the HCl gas diffuses from the other. When they meet they form Ammonium chloride.
4. The ring forms nearest to where the HCl gas was
5. This is because the particles of ammonia are smaller and lighter than the particles of hydrogen chloride and so diffuse through the air quicker

Bromine gas and air-

1. Bromine gas to brown and has a strong smell
2. Fill half a gas jar full of bromine gas and the other half full of air- separate the gases with a glass plate
3. When the glass plate is removed you'll see the brown bromine gas slowly diffuse through the air
4. The random motion of the particles means that the bromine will eventually diffuse right through the air

Atoms are made up of the nucleus (which contains protons and neutrons) and electrons which move around the nucleus

Molecules are groups of atoms

Elements consist of only one atom

Compounds are chemically bonded atoms

Mixtures are easily separated compounds as there is no chemical bond between them

Separating of mixtures:

• Filtration- used to separate an insoluble solid from a liquid
• Crystallisation- used to separate a soluble solid from a solution
• Chromatography- separate out mixtures, usually dyes. It works because different dyes move up the paper at different rates
• Simple distillation is used to separate out solutions using heat
• Fractional distillation is used to separate a mixture of liquids, for example crude oil

1a) States of Matter

Solids:

• Have strong forces of attraction between particles which holds them close together in fixed positions to form a very regular lattice arrangement
• Particles vibrate

Liquids:

• Have weak forces of attraction between particles and are randomly arranged so they don't have a definite structure/shape
• They are constantly moving in a random motion

Gases:

• Are free to move because the forces of attraction are very weak
• The particles travel in a straight line
• Random motion
• Don't have a definite shape   

Changes to the arrangement or energy of particles 

Movement of particles 
Diffusion: molecules move and spread randomly due to bumping into each other
Lighter particles travel faster

Section 1

Principles of Chemistry