Chemistry IGCSE (Paper 1 ONLY)

• Particles touching each other

• Regular arrangement

• Vibrate about fixed positions but don’t move apart

• Stronger force between particles than in a liquid

• Not compressible

• Particles close + touching each other - more spaced than solid

• Irregular particle arrangement

• Particles move around and slide past each other

• Forces between particles not as strong as a solid

• No fixed shape (takes shape of its container)

• Not compressible

• Particles far apart

• Irregular particle arrangement

• Particles move freely + collide with each other

• Very weak forces between particles

• No fixed shape or volume

• Compressible

= melting

Solid heated → particles get energy → vibrate more violently → at certain temp. particles have enough energy to break free from position

= evaporating

Liquid heated → particles get more energy → move faster, weakening + breaking bonds holding liquid together → at certain temp, particles have enough energy to break bonds

= freezing

Requires significant temp. decrease + occurs at specific temp, different for each substance

= condensing

Gas cooled → particles lose energy → when particles collide, don’t have enough energy to bounce back → group together to form liquid

= sublimation

only happens to a few solids

• Put potassium manganate(VII) at bottom of water beaker

• Purple colour slowly spreads out to fill beaker

• Particles of potassium manganate(VII) diffuse out among particles of water

• Random motion of particles in liquid causes purple colour to eventually be evenly spread out in water

Dilution: If you added more water to final solution of potassium manganate, particles would spread further + solution would be less purple

• Aqueous ammonia (NH₃) gives off ammonia gas

• Hydrochloric acid (HCl) gives off hydrogen chloride gas

• Set up experiment as in diagram → white ring of ammonium chloride forms in tube

• NH₃ gas diffuses from one end of tube + HCl gas diffuses from other → form ammonium chloride when they meet

• Ring doesn’t form exactly in middle - forms nearest end of hydrochloric acid

• Because ammonia particles are smaller + lighter so diffuse through air quicker

• Bromine gas: brown, strong-smelling

• Fill half a gas jar full of bromine gas + other half full of air - separate gases with glass plate

• Remove glass plate → brown bromine gas diffuses slowly through air

• Random motion of particles means that bromine will eventually diffuse right through air

substance being dissolved

liquid that solute dissolves in

mixture of solute + solvent that doesn’t separate out

solution where max amount of solute has been dissolved - no more solute will dissolve in solution at that temperature

consist of one type of atom only
e.g. oxygen, copper

• material composed of 2+ elements/compounds

• physically mixed together

• no chemical bond

• properties of mixture are mixture of properties of separate parts

• e.g. air (mixture of several gases), crude oil (mixture of hydrocarbons, mostly liquids)

• made up of atoms of 2+ different elements joined by chemical bonds

• properties often totally different from properties of original elements

• e.g. carbon dioxide is compound formed from chemical reaction, one C atom reacts with two O atoms to form molecule of carbon dioxide

• Made of single element/compound

• Has specific melting + boiling point
  e.g. pure ice melts at 0ᵒC, pure water boils at 100ᵒC

• Mixture not pure - will melt/boil gradually over range of temperatures

used to separate insoluble solid from a liquid/solution

1. Put filter paper in funnel and pour in mixture

2. Liquid part runs through paper, leaving behind solid residue

used to separate soluble solid from solution

1. Pour solution into evaporating dish + gently heat solution
   Some water will evaporate, solution becomes more concentrated

2. Once some water has evaporated/when crystals start to form, remove dish from heat + leave solution to cool

3. Salt should start to form crystals as it becomes insoluble in cold, high conc. solution

4. Filter crystals out of solution + leave in warm place to dry

used to separate dyes

1. Draw line near bottom of filter paper (use pencil as pencil marks are insoluble so won’t dissolve in solvent)

2. Add spots of diff inks to the line at regular intervals

3. Loosely roll sheet up + put in beaker of solvent e.g. water

4. Ensure level of solvent is below baseline - don’t want inks to dissolve in solvent

5. Put lid on container to stop solvent evaporating

6. Solvent seeps up paper, carrying inks with it

7. Each dye in inks moves up paper at diff rate + forms spot in diff place

8. When solvent has nearly reached top of paper, take paper out of beaker + leave to dry

9. End result is called chromatogram

• Different dyes move up paper at different rates

• Some stick to paper, others dissolve more readily in solvent + travel quicker

• Distance travelled by dyes depends on solvent + paper used

Rf = distance travelled by solute/distance travelled by solvent

1. To find distance travelled by solute, measure from baseline to centre of spot

2. Chromatography often used to see if certain substance is in mixture
   Run a pure sample of substance you think might be in mixture alongside sample of mixture itself
   If sample has same Rf values as one of the spots, they’re likely to be same

used to separate pure liquid from solution

1. Heat the solution
   Part of solution with lowest BP evaporates

2. Vapour is cooled, condenses + collected

3. Rest of solution is left behind in flask

4. Can use simple distillation to get pure water from seawater
   Water evaporates, condenses and is collected

Problem: can only be used to separate things with very different BPs

used to separate mixture of liquids with different boiling points

1. Put mixture in flask + put fractionating column on top, then heat it

2. Different liquids have different BPs so evaporate at diff temps

3. Liquid with lowest BP evaporates first
   When temp on thermometer matches BP of liquid, it reaches top of column

4. Liquids with higher BPs also start to evaporate but column is cooler towards top, so they only get part of the way up before condensing + running back down towards flask

5. When first liquid has been collected, raise temp until next one reaches the top

smallest particle of element
consists of electrons surrounding a nucleus that contains protons + neutrons

group of 2+ atoms chemically joined together

number of protons in nucleus of atom

sum of number of protons + neutrons in nucleus of atom

atoms of same element with same atomic number but different mass number

average mass of atom of an element
measured as ratio 1/12 of mass of atom of carbon-12

• Multiply % abundance of each isotope by its mass

• Add these numbers together

• Divide by total abundance (100%)

• Ordered in order of increasing atomic number

• Columns = groups

• Rows = periods

• have same number of electrons in outer shell

• have similar properties

• Properties of elements depend on number of electrons

• Number of electrons in outer shell is most important

Electrons occupy shells

1st shell: 2
2nd shell: 8
3rd shell: 8

• Period of element = number of shells containing electrons

• Group number = number of electrons in outer shell

• e.g. Sodium in period 3 so has 3 shells occupied
  First two shells must be full (2.8)
  In group 1 so has 1 electron in outer shell
  So electronic configuration = 2.8.1

• Elements on left of zigzag are metals

• Metals conduct electricity because they allow charge to pass through them easily

• Metal oxides are basic - they neutralise acids
  Metal oxides which dissolve form solutions with pH of 7+

• Elements on right of zigzag are non-metals

• Non-metals are poor electrical conductors

• Non-metal oxides are acidic - they neutralise base
  They dissolve in water to form solutions with pH less than 7

• Called noble gases, including helium, neon, argon

• Inert - don’t react much

• → takes a lot of energy to add/remove electrons from full outer shell of noble gas atom

Reactants + products of reaction
Can write word equations or chemical (symbol) equations

(s) - solid

(l) - liquid

(g) - gas

(aq) - aqueous (dissolved in water)

• Put numbers in front of formulas where needed

• Find an element that doesn’t balance, write a number to try sort it out

• See where it gets you. May create another imbalance, if so, write another number and see where that gets you.

• Carry on correcting unbalanced elements until it solves

Sum of relative atomic mass of all atoms

Unit for amount of substance

One mole of atoms/molecule of a substance has mass in grams equal to relative particle mass for that substance

Mass of one mole, measured in grams

Number of Moles = Mass in g / Mᵣ

• Work out balanced equation

• Work out Mᵣ of reactant + product you’re interested in

• Find number of moles of the substance you know of

• Use balanced equation to find how many moles there’ll be of other substance

• Use number of moles to calculate mass

• Calculate theoretical yield using balanced equation

• Percentage yield = actual yield/theoretical yield x 100

• 100% yield means you got all the product you expected

Smallest whole number ratio of atoms in a compound

• List all elements in compound

• Write their experimental masses underneath

• Find number of moles of each element

• Turn numbers into ratio by dividing by smallest number of moles

• Get ratio in its simplest whole number form

Actual number of atoms of each element in a compound

1. Find the mass of empirical formula

2. Divide molecular mass by formula mass

3. Multiply empirical formula by number obtained in step 2

• Get crucible and heat until red hot (ensures that it’s clean and no traces of oil/water left)

• Leave crucible to cool, then weigh it, along with lid

• Add some clean magnesium ribbon to crucible
  Reweigh crucible, lid and magnesium ribbon

• Heat crucible containing magnesium
  Put lid on crucible to stop bits of solid escape, but leave small gap to allow oxygen to enter crucible

• Heat crucible strongly for around 10 mins

• Allow crucible to cool and reweigh crucible with lid + contents

• Use mass of magnesium oxide and initial mass of magnesium to calculate empirical formula

• Place rubber bung (with hole in middle) into test tube with small hole in end
  Weigh them using balance

• Take bung out of test tube + spread small amount of copper(II) oxide in middle of tube

• Re-insert bung + weigh test tube again

  Set up equipment as in diagram

• Expel air from test tube by gently turning on gas
  After 5 secs, light gas by holding burning splint next to hole in end of tube

• Use Bunsen burner to heat copper(II) oxide for 10 mins

• Turn off Bunsen burner + leave tube to cool

• Once tube has cooled, turn off gas and weigh tube with bung + contents

• All solid salts consist of lattice of +ve and -ve ions

• In some salts, water molecules are incorporated into lattice

• Water in lattice = water of crystallisation

• Solid salt containing water of crystallisation is hydrated

• If salt doesn’t contain water of crystallisation, it’s anhydrous

• One mole of hydrated salt always has particular number of moles of water of crystallisation - formula shows how many

• e.g. hydrated copper sulfate has 5 moles of water for every one mole of salt
  So formula is CuSO₄.5H₂O (dot between CuSO₄ and 5H₂O)

• Many hydrated salts lose water of crystallisation when heated to become anhydrous

when atoms lose/gain electrons
Negative ions (anions) form when atoms gain electrons
Positive ions (cations) form when atoms lose electrons

Groups 1, 2, 3 are metals. They lose electrons to form +ve ions.

Groups 5, 6, 7, are non-metals. They gain electrons to form -ve ions.

Elements in same group have same number of electrons in outer shell
So can lose/gain same number of outer electrons
So form ions with same charge

Ag⁺

Cu²⁺

Fe²⁺

Fe³⁺

Pb²⁺

Zn²⁺

H⁺

OH⁻

NH₄⁺

CO₃²⁻

NO₃⁻

SO₄²⁻

transfer of electrons

• When metal + non-metal react, metal atom loses electrons to form positive ion and non-metal gains these electrons to form negative ion

Ionic compounds are made up of positively charged part + negatively charged part

Overall charge of ionic compound = 0

So negative charges must balance positive charges

• Dots represent electrons from one of the atoms

• Crosses represent atoms from the other atom

Electrostatic attraction between oppositely charged ions

• Compounds with ionic bonding have giant ionic structures

• Ions held together in closely packed 3D lattice

• Electrostatic attraction between oppositely charged ions is very strong

• → a lot of energy needed to overcome strong attraction

• → high melting + boiling points

• Solid - don’t conduct electricity

• Molten/in aqueous solution - conduct electricity

• Atoms make covalent bonds by sharing pairs of electrons with other atoms

• Each covalent bond provides 1 extra shared electron for each atom

the strong electrostatic attraction between negatively charged pair of electrons and positively charged nuclei of the atoms involved

• Atoms within molecule are held together by very strong covalent bonds

• But forces of attractions between molecules are very weak

• → weak intermolecular forces = very low melting + boiling points, because molecules are easily separated

• Are gases/liquids at room temp or solid with low melting + boiling points

have stronger intermolecular forces than smaller molecules

• Because there are more points along the larger molecules for intermolecular forces to act between them, so more energy needed to break forces

• → melting + boiling points of simple molecular substances increase as relative molecular mass increases

• All atoms bonded to each other by strong covalent bonds

• Lots of bonds → takes lots of energy to break them

• → have very high melting + boiling points

• Don’t conduct electricity - even when molten (except for graphite)

• Made of network of carbon atoms that each form four covalent bonds

• High melting point - strong covalent bonds take lots of energy to break

• Very hard - strong covalent bonds hold atoms in rigid lattice structure

• Doesn’t conduct electricity - no free electrons/ions

• Each carbon atom forms three covalent bonds, creating layers of carbon atoms

• Soft + slippery - layers are held together weakly by intermolecular forces, so are free to slide over each other

• High melting point - covalent bonds in layers need lots of energy to break

• Conducts electricity - only 3 out of carbon’s 4 outer electrons are used in bonds, so each C atom has 1 delocalised (free) electron that can move

• Hollow spheres made of 60 carbon atoms

• Not a giant covalent structure - made of large covalent molecules

• Soft - C₆₀ molecules only held by weak intermolecular forces so can slide over each other

• Poor electrical conductor - has 1 delocalised electron but electrons can’t move between molecules

• Elements in same group react similarly

• e.g. lithium, sodium, potassium react vigorously in water

• Reaction produces metal hydroxide solution
  Solution is alkaline → Group 1 = alkali metals

• Reaction of alkali metals with water also produces hydrogen → causes fizzing

Group 1 metals can react with oxygen in air to form metal oxides

Different types of oxide form depending on the Group 1 metal

Forms lithium oxide (Li₂O)

Forms mixture of sodium oxide (Na₂O) and sodium peroxide (Na₂O₂)

Forms mixture of potassium peroxide (K₂O₂) and potassium superoxide (KO₂)

• As you go down Group 1, elements are more reactive

• This can be seen with rate of reaction with water

• Lithium takes longer than sodium + potassium to react, so it’s least reactive

• Potassium takes shortest time to react, so it’s most reactive

• Trend of reactivity can be seen in reaction between alkali metals + oxygen
  Potassium reacts quicker than sodium + lithium when left in air

• This trend shows that the elements further down the group (e.g. caesium) are more reactive

As atomic number increases:

• darker colour

• higher boiling point

• Fairly reactive

• Poisonous

• Green gas

• Poisonous

• Red-brown liquid

• Gives off orange vapour at room temp.

• Dark grey crystalline solid

• Gives off purple vapour when heated

• 78% nitrogen

• 21% oxygen

• 0.9% argon

• 0.04% carbon dioxide