Chemistry Revision Cards

Atoms

The nucleus contains protons and neutrons, meaning almost the whole mass is concentrated here. The electrons orbit the nucleus and occupy shells.

Protons have a mass of 1 and a charge of +1

Neutrons have a mass of 1 and a charge of 0

Electrons have a mass of 0.0005 and a charge of -1

The number of protons equals the number of electrons

Elements, Compounds and Isotopes

Elements consist of only 1 type of atom

Compounds are chemically bonded. Compounds are when two or more elements chemically bond together. Their properties are different to that of the original element.

Isotopes are the same, apart from they have a different amount of neutrons from each other.

Isotopes are different atomic forms of the same element which contain a different number of neutrons but the same number of neutrons.

Electron Shells

Electrons always occupy shells (they may be referred to as energy levels).

The lowest energy levels are always filled first - these are the ones closest to the nucleus.

Only specific amounts of electrons are allowed into each shell: 1st shell = 2, 2nd shell = 8, 3rd shell = 8.

When the outer shell is not full, the atoms want to react. The noble gases in Group 0 have full outer shells, so are therefore unlikely to react.

Ionic Bonding

Atoms tend to lose or gain electrons to form charged particles - ions. Ions are strongly attracted to ions of the opposite charge.

An atom with 1 electron is more likely to get rid than gain 7 electrons, whereas an atom with 7 electrons in it's outer shell is more likely to gain 1 than lose 7. - It takes less effort.

Giant Ionic structures are formed by ionic bonds. The atoms are closely packed together to form a lattice structure. There is very strong chemical bonds between each atom making them have a high melting point.

Giant Ionic Structures

They have high melting points due to the very strong chemical bonds each ion holds with others.

They dissolve to form an eletricity conducting solution. When dissolved the ions have the freedom to move meaning the have the ability to carry a charge.

THey conduct electricity when they are molten too. When it melts, the ions are, again, free to move and they carry a current. 

Electron Shells and Ions

Groups 1 & 2 and 6 & 7 are the most likely to form ions.

Group 1 and 2 elements are metals and they lose electrons to form positive ions (can be referred to as cations).

Group 6 and 7 elements are non-metals. They gain electrons to form negative ions (can be referred to as anions).

When cations react with anions, they form ionic bonds. Only elements of opposite charges may form ionic bonds.

Covalent Bonding

Covalent Bonding means sharing electrons. This way, both atoms have a full outer shell. Each covelent bond provides one extra shared electron for each atom. Each atom involved has to make enough covalent bonds in order to sill its outer shell.

Hydrogen  H (little 2) - Hydrogen atoms have just one electron. They only need one more to complete the first shell.

Ammonia NH (little 3) - Nitrogen has 5 outer electrons, so it needs to form three covalent bonds in order to fill its outer shell.

Oxygen  O (little 2) - Oxygen has six outer electrons. They sometimes form Ionic Bonds by taking the two extra electrons to complete its shell. However they can form covalent bonds and share two electrons instead.

Giant Covalent Structures

Similar to giant ionic structures apart from, there are no charged ions. All the atoms are bonded to each other by strong covalent bonds. They have very high melting and boiling points. They don't conduct electricity. They're usually insoluable in water.

Diamond - Each carbon atom forms four covalent bonds in a very rigid giant covalent structure. This structure makes diamond the hardest natural substance.

Graphite - Each carbon atom only forms three covalent bonds, creating layers which have the ability to slide over each other. The layers are held together very loosely that they can be rubbed off. It also leaves free electrons, so graphite is the only non-metal which is a good conductor of electricity.

Metallic Structures

Metal properties are down to the free electrons. Metals also consist of a giant structure, Metallic bonds involve free electrons, which produce all of the properties of metals. These free electrons come from the outer shell of every atom in the structure. These electrons are free to move, meaning these metals are good conductors of electricity,

These electrons also hold the atoms together in a regular structure. They allow the atoms to slide over each other, causing metals to be malleable.

Nanomaterials

Really tiny particles, 1-100 nanometres across, are called 'nanoparticles'. Nanoparticles include fullrenes. These are molecules of carbon, shaped like hollow balls or closed tubes. The smallest fullerene is buckminister fullerene, which has sixty carbon atoms joined in a ball.

Fullerenes can be joined together to form nanotubes. A nanoparticle has very different properties to the bulk chemical it is made from. E.g. fullerenes have different properties from atoms of carbon.

All those covalent bonds make carbon nanotubes very strong. They can be used to reinforce graphite in tennis rackets and a lot more. Nanotubes conduct electricity, so they can be used in tiny electric circuits for computer chips,

Balancing Equations

Reactants --> Products

Magnesium reacts with oxygen to produce magnesium oxide.                             2Mg + O2 --> 2MgO

There must always be the same number of atoms on both sides. You balance the equation by putting numbers in front of the formulas where needed.

Balance just ONE type of atom at a time. Find an atom that doesn't balance and pencil in a number to try and sort it out. Carry on doing this and it should eventually balance. (:

Relative Formula Mass

This is just a way of saying how heavy different atoms are. The relative atomic mass is usually just the same as the mass number of the element.

The relative formula mass is just all the relative atomic masses added together. For MgCl2 it would be 24 + (35.5 x 2) = 95.

Calculating % Mass

Percentage mass of an element in a compound =

(the relative atomic mass x the number of atoms (of that element) divided by the relative formula mass of the whole compund) x 100

Example. Find the percentage mass of sodium in sodium carbonate. Na2CO3 Answer. Sodium = 23, Carbon = 12, Oxygen = 16

Relative formula mass of sodium chloride = (2 x 23) + 12 + (3 x 16) = 106

(23 x 2) divided by 106 x 100 = 43.4%

Empirical Formula

1) List all the elements in the compound

2) Underneath, write their experimental masses or percentages

3) Divide each mass or percentage by the relative atomic mass for that particular element.

4) Turn the numbers you get into a nice simple ratio by dividing them by a common factor

5) Get the ratio into its simplest form.

Calculating Masses in Reactions

1) Write down the balanced equation. 2) Work out the relative formula mass just for the part(s) you want. 3) Apply the rule: Divide to get one, then multiply to get all

Example. What mass of magnesium oxide is produced when 60g of magnesium is burned in air.

1)  2Mg + O2  --> 2MgO

2)  (2 x 24) 48 --> (2 x (24 + 16)) 80

3)  48g of Mg ... reacts to give ... 80g of MgO

     1g of Mg ... reacts to give ... 1.67g of MgO

     60g of Mg ... reacts to give ... 100.2 g of MgO

The Mole

Number of Moles = Mass in grams of the element or compound divided by the relative formula mass of the element  or compound.

Example. How many moles are there in 42 g of Carbon?

Answer. No. of moles = Mass (g) / Mr = 42/12 = 3.5 moles

Number of Moles = Volume in litres x moles per litre of solution

Example. How many moles in 185 cm3 of a 2M solution? Answer. 0.185 x 2 = 0.37 moles.

Atom Economy

Atom Economy = total relative formula mass of useful products divided by total relative formula mass of reactants multiplied by 100.