Chemistry C2

Metal + Non Metal.

• Metal = Positive
• Non Metal = Negative

The bond created is STRONG. In ionic bonding you end up with a ionic structure/lattice.

Atoms are most stable when they have a full outer shell.

For example:

Sodium has one electron in it's outer shell and chlorine has seven electrons in it's outer shell.

Sodium has given chlorine an electron so they both have a full outer shell which will make them stable.

This will make them ions because sodium will be positively charged and chlorine will be negatively charged. 

These can then react to form a compound. A compound is a substance where the atoms of two or more elements are combined.

A chemical bond is where atoms transfer or share electrons in the outer shell.

Group 1 in the Periodic Table:

• All produce ions with a charge of +1
• Alkali metals

Group 7 in the Periodic Table:

• All produces ions with a charge of -1
• Halogens - ion is called hallide

Group 0 in the Periodic Table:

• Full outer shell
• Unreactive

Isotopes are a version of an element with the same number of protons but a different number of neutrons.

A:

• 8 protons
• 8 neutrons

B:

• 8 protons
• 10 neutrons

C:

• 5 protons
• 6 neutrons

A and B are isotopes because they have the same number of protons but a different number of neutons.

O=O

• Share two electrons
• Shows covalent bond (strong)

• low melting and boiling points
• atoms are held together by covalent bonds
• no overall electric charge so don't conduct electricity

examples:

• hydrogen
• methane
• oxygen
• ammonia

Covalent bonds are strong but the intermolecular forces are weak.

Boiling or melting these substances requires energy to overcome the weak intermolecular forces of attraction.

A giant ionic lattice is held together by strong electrostatic forces.

Ionic compunds have a high melting and boiling points because large amounts of energy is needed to break the forces.

AKA Macromolecules

Diamond (a form of carbon) joined together by covalent bonds. This means it has a high boiling and melting point.

Carbon is a very hard substance because it is covalently bonded to four of it's neighbours.

Graphite (a form of carbon) is only linked to three of it's neighbours. This means that the layers are able to slide over eachother easily so it has weak intermolecular forces. This makes it a soft slippery substance that conducts heat and electricity.

Each carbon atom has a delocalised electron because it is only bonded to three.

The particles in a metal are held together by strong metallic bonds.

Electrons in an outer shell of an atom are delocalised which leaves an atom with a positive charge. (electrons are negative)

Positive ions interact with delocalised electrons so there is a strong electrostatic attraction.

Buckminster Fullerene is mainly hexagon shapes. It can be used for:

• Drug delivery in the body. The molecule of the drug can be caged in the fullerene molecule.
• Lubricant.
• Catalyst - it has a large surface area.

Nanotube is all hexagon shapes. It can be used for:

• Reinforcing materials like tennis rackets.

Look for pictures on google!

Atoms in a metal are in rows and columns so it is easy for them to slide over eachother. This makes it easy for metals to be hammered/bent into shape.

An alloy is a mixture of metals. The second metal's atoms disrupt the shape so the atoms can't slide and move as easily.

e.g

Nitonol - Nickel and Titanium. It can be bent but when it is warmed up it goes back to it's original shape. It can be used for:

• Braces
• Repair broken bones

This is because the warmth of the body can make it contract, as it is going back to it's original shape, making it tighter around the teeth/bone.

Metals are good conductors because metals have electrons in the outer shell of the atoms which are delocalised.

Conducting Heat:

Electrons are free to move so when heated they gain energy, this makes them vibrate and move faster making it easier for them to bump into other electrons and atoms to pass on the heat.

Conducting Electricity:

Electrons are free to move to carry the electricity along the material.

If there is a charge either side of the metal the electrons will be attracted to the positive. So will move through the metal to get there making electricity flow through the metal.

Ethene is monomilised to poly(ethene), a chain of monomers. This is plastic.

With high pressure and low carbon dioxide you can get low density poly(ethene). --->

• polymer chains are far apart
• lower melting point
• softer
• weak forces of attraction

With a raised pressure (50degrees) and a certain catalyst you can get high density poly(ethene). --->

• high melting point
• polymer chains are close together
• harder
• strong forces of attraction

Thermosoftening

• Chains are fairly tangled
• Chains are easy to seperate
• Can be melted easily
• Good for recycling
• Used for bottles and containers

They are easy to melt and seperate out because:

• Weak intermolecular forces
• Polymers can seperate easily at low temperatures so less heat energy is needed.

Thermosetting

• long chains with covalent bonds which link the polymer chains
• high melting point
• can't be remoulded
• can be used for spatulas, pan handles, plug sockets

Nanoparticles are 1-100nm (very,very small) and have a very large surface area to volume ratio.

Can be used for:

• Catalyst to speed up chemical reactions because of their large surface area so can be used in the chemical industry
• Large surface area helps absorb more UV light so can be used in cosmetics like sun tan cream and deodrant
• Can be used in the medical industry for drug delivery (buckminster fullerene), antiviral and antifungal
• Can make a stronger or lighter material so can be used in construction (nanotube for tennis rackets making them light)
• Computers to make tiny circuits 

In the nucleus of an atom there is protons and neutrons which make up the mass number. Around the outside in shells are electrons.

The number of protons and electrons are the same to balance eachother out.

Protons:

• charge - +1 positive
• mass - 1

Neutrons:

• charge - no charge
• mass - 1

Electrons:

• charge - -1 negative
• mass - very small

If two of the same element have different number of neutrons they are isotopes however there proton number shoud be the same. The change in the number of neutrons affects the mass number.

The relative atomic mass is compared to carbon 12. Carbon 12 has a mass number of 12 and a proton number of 6.

On the periodic table is shows you the average mass number of the isotopes of an element. 

For example a hydrogen could have 24 as it's mass number and 12 as it's proton number. This will be 2x carbon 12.

Relative Formula Mass is the Ar of all the compound.

H2O 

Ar for H = 1

Ar for O = 16

Mr: (1x2)+16=18

Al2(SO4)3

Ar for Al = 27

Ar for S = 32

Ar for O = 16

Mr: (27x2)+3(32+64)=342

Paper chromatography is a chemical analysis used to identify additives in food.

1. On a chromatography paper draw a pencil line and add a sample of what you want to analyse on the pencil line

2. Put in the end of the paper in a beaker of solvent, don't put the sample in the solvent

3. Put a lid on to prevent evaporation

4. Allow the solvent to rise up the paper, this will dissolve the sample

5. Colours will seperate out because some of the sample will dissolve quicker than others so will be further up the paper

6. Compare with a chromatogram, this has known samples on it so you can compare and see what additives your sample has in it

• Sample is vaporised and passed through a column
• A gas (usually nitrogen) moves it through the column
• The chemicals are carried through the column at different speeds so they seperate out
• A detector detects the different chemicals in the sample and shows them as a peak on a chart
• You can compare the reading you got with known samples

A mass spectrometer is an extra analysis tool to identify the substances

From the mass spectrum you can work out the molecular mass

A mass spectrometer can identify chemicals quickly and accurately. It is very sensitive so it can even detect small amounts. 

To work out the percentage by mass you can use the formula:

relative atomic mass of the element / relative formula mass of the compound x 100

A mole is an amount (6.02x1023)

One mole of an element has a mass which is the same as the relative atomic mass (g).

H2O

3 moles of H2O have a mass of:

Ar of H = 1

Ar of O = 16

1 mole = 18g

3 moles = 54g

In a reversible reaction the products can react to produce the original reactants again.

An example:

anhydrous copper (II) sulphate + water = hydrated copper (II) sulphate

This reaction is used to test for water.

The white solid will turn blue in the presense of water.

If you heat the hydrated copper it will turn white because the water will be driven off, this make it anhydrous copper. When you add water to it again it will turn blue, it has turned back to hydrated copper.

If you have a balanced equation for a reaction you can calculate the masses of the reactants.

CaCO3 ------> CaO + CO2

If we have 50g of CaCO3, how much CaO can we make?

1. Work out the Mr of both compounds.

2. This means 100g of CaCO3 makes 56g of CaO.

3. 50g is half so we divide by 2. This means the answer is 28g.

We can use information about reacting masses to calculate the formula of a compound. e.g 3.2g of sulphur reacts with oxygen to produce 6.4g of sulphur oxide. What is the formula of the oxide?

Step 1. Find the masses.

• Sulphur 3.2g
• Oxygen 3.2g

Step 2. Look up Ar.

• Sulphur 32
• Oxygen 16

Step 3. Divide masses by Ar.

• Sulphur 0.1
• Oxygen 0.2

Step 4. Find ratio = 1:2

Answer = SO2

Exothermic reactions transfer energy to the surroundings. The energy is usually transferred as heat energy causing the reaction mixture and surrounding to become hotter.

Examples of exothermic reactions:

• combustion (burning)
• many oxidation reactions (rusting)
• neutralisation reactions between acids and alkalis

They can be used for everyday purposes like:

• handwarmers
• self heating cans

Endothermic reactions take in energy from the surroundings. This causes the reaction mixture and surroundings to get colder.

Examples of endothermic reactions:

• electrolysis
• reaction between ethanoic and sodium carbonate
• thermal decompisition of calcium carbonate in a blast furnace

Everyday purposes of endothermic reactions:

• Sports injury cold pack

Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. Electricity is the flow of electrons or ions. For electrolysis to work the compound must contain ions. The ions must also be free to move which is possible when a substance is dissolved in water or melted.

During elctrolysis positively charged ions move to the negative electrode. They receive electrons and are reduced. Negatively charged ions move to the positive electrode where they lose electrons and are oxidised.

The substance broken down is called the electrolyte. To be an electrolyte a substance must be able to conduct electricity.

Carbon electrodes are mostly chosen because they have a high melting point and will not react with reactants and products.

The metal is formed at the cathode (negative electrode) because the positive metal ions are attracted to it. The non metal is formed at the anode (positive electrode) where the negative ions are attracted.

Electrolysing aqueous solutions of ionic compounds can be more complicated than electrolysing molten compounds because the water molecules can provide hydrogen ions (H+) and hydroxide ions (OH-)

Metals and hydrogen are both positive. Whether you get hydrogen or a metal at the negative electrode depends on where the metal is in the reactivity series. The metal will be produced if it less reactive than hydrogen.

If the negative ion is more complex e.g NO3- then oxygen will be produced at the positive electrode instead.

A half equation shows you what happens at an electrode during electrolysis. Electrons are shown as e-. A half equation is balanced by adding or taking away a number of electrons equal to the total number of charges on the ions in the equation.

The amount of charge transferred during electrolysis can be calculated from the mean current used and the time taken.

charge = current x time

coulombs = amps x seconds

Electrolysis is used to electroplate objects. This is useful for coating cheaper metals with expensive ones.

• The negative electrode should be the object that is to be electroplated
• The positive electrode what you want to coat the object with
• The electrolyte should be a solution of the coating

A salt is any compound formed by the neutralisation of an acid by a base. The name of a salt has two parts. The first part comes from the metal, the second part comes from the acid.

Nitric Acid always produce salts that end in nitrate and contain NO3-

Hydrochloric acid always produce salts that end in chloride and contain the chloride ion Cl-

Sulfuric acid always produce salts that end in sulfate and contain the sulfate ion SO4 2-

To make an insoluble salt, two soluble salts need to react together in a precipitation reaction.

Silver chloride is an insoluble salt. It can be made by reacting a soluble silver salt with a soluble chloride salt.

silver nitrate + sodium chloride ------> sodium nitrate + silver chloride

AgNO3(aq) + NaCl(aq) ------> NaNO3(aq) + AgCl(s)

The silver chloride appears as tiny particles suspended in the reaction mixture, this is the precipitate. The precipitate can be filtered, washed with water on the filter paper and dried in the oven.

Soluble salts can be made by reacting acids with either soluble or insoluble bases.

Effect of increased temperature:

• reactant particles move quickly
• have more energy
• particles collide more often so more collisions are successful
• rate of reaction increases

Effect of increased concentration and pressure:

• the reactant particles become more crowded
• greater chance of particles colliding
• rate of reaction increases

Effect of increased surface area of the reactant:

• more particles exposed to the other reactant
• more collisions 
• rate of reaction increases

The rate of reaction can increase by adding the suitable catalyst. A catalyst is a substance which changes the rate of reaction but is unchanged at the end of the reaction.

Different catalysts catalyse different reactions.

Not all reactions have suitable catalysts.