chem paper 1

Proton: 1, +1 Neutron: 1, 0 Electron: Negligible, -1

Average mass of atoms of that element taking into account the mass and amount of each isotope it contains, on a scale where the mass of a C-12 atom is 12

((mass no.1×%abundance)+(mass no.2×%abundance)+⋯)/100

John Dalton: Atoms could form compounds

JJ Thompson: Before the discovery of the electron, atoms were thought indivisible. The electron led to JJ Thompson's plum pudding model (ball of positive charge with e- embedded in it).

Ernest Rutherford: After the Gold foil experiment (fired alpha particles at thin gold foil), Ernest Rutherford, concluded that the mass of at atom was concentrated at the centre, in a charged nucleus and most of the atom was empty space. If the plum pudding were correct, then all the particles would go straight through, but some bounced back (hit hard, dense nucleus), some veered off (repelled by positive nucleus), and some went through (empty space)

Niels Bohr: Energy levels (the electrons in an atom occupy the lowest available energy levels/shells until given energy)

Further experiments concluded: Positive charge of the nucleus could be divided into protons

James Chadwick: Proved the existence of neutrons within the nucleus.

All fast, highly charged alpha particles would pass through unhindered. This is because the positive charge and mass in the plum pudding model would be spread out throughout the entire very large volume of the atom, so in a single point that a tiny alpha particle would pass through, the charge would be too low to deflect it.

1. Positive charge - spread throughout in PP vs in centre in N

2. Negative charge - spread throughout ball of positive charge in PP vs electrons orbiting nucleus in N

3. Neutrons - none in PP vs in nucleus in N

4. Space - atom is solid with no empty space in PP vs atom mostly empty space in N

5. Mass - spread evenly throughout in PP vs in centre in N

Atomic mass: The sum of protons and neutrons (bottom) Atomic number: a unique number of protons = electrons (if atom) (top)

by increasing atomic number in groups of similar properties (occur at relative intervals - periodicity), and valency in periods of occupied electron shells

RAM = (Mass no x abundance) + (Mass no. x abundance) / 100

positive

negative

• Gases

• Unreactive due to stable electron configuration

• Rarely form compounds

• Have full outer shell

• The boiling points of the noble gases increase with increasing relative atomic mass (going down the group)

• Density increases down the group as atoms have higher RAM

• Do not form ions

• Metals

• Appearance: dull when exposed to air and shiny

• Very easy to cut and easier as you go down

• Low densities. Less dense than water for first 3 and density increases down (potassium is an anomaly)

• Relatively low melting points, decreasing as the atoms get bigger going down the group

• All are very reactive due to valency of 1. The reactivity of the elements increases going down the group because of the increasing distance between the nucleus and the outer electron down the group, which results in a decreased force of attraction so it is lost easier

• Reaction with water is more vigorous as you go down. It produces effervescence, an alkali solution (the metal dissolves), hydrogen and it is exothermic

• Form white compounds

• When reacting with water, forms alkaline solution

(As you go down the group, the metallic force of attraction decreased due to the sea of delocalized electrons being further away from the positive ions, so it easier to cut, and the melting and boiling points decrease. The density increases as you go down the group because there is a higher increase in mass than volume)

4Alkali metal + O₂(g) -> 2[Alkali metal]₂O(s) The metals burn with different colour flames

Alkali metal + H₂0(l) -> [Alkali metal]OH(aq) + 1/2 H₂(g) All react with water to produce hydrogen gas (effervescence) and an alkaline solution containing metal hydroxide (metal dissolves). Exothermic reaction

2Alkali metal + Cl₂(g) -> 2[Alkali metal]Cl(s) All burn in chlorine to form metal chlorides which are white powders

Fizzes, moves on the surface of the water

Fizzes, melts into a ball, burns with lilac flame (hydrogen ignites), moves on the surface of the water

Explosive reaction

When the melting and boiling points come together so liquid state is skipped

• Non-metals

• Diatomic (exist in covalently bonded pairs to become stable)

• They make halide salts (e.g. Chlorine in Sodium Chloride)

• All are very reactive as they need only one electron to become stable and the reactivity decreases down the group because the distance between the outer shell and nucleus increases, so the electron is weakly attracted, and so in a displacement reaction (e.g. in a salt), the halogens would switch places when they come together as the electron is then more strongly attracted to the other nucleus so it moves and the halogen displaces the other

• Low melting/boiling points, increase down the group as the atoms get heavier

Fluorine: pale yellow gas Chlorine: pale green gas Bromine: Dark brown liquid w/orange gas Iodine: grey solid (as a gas - 184°C - violet)

Compounds made from Halogens

Cl₂ + 2KI -> 2KCl + I₂

• Found in the D-block (not all elements in the D-block are transition metals

• First row is Titanium - Copper

• Many can form ions with different charges (e.g. Iron (II) oxide)

• Form coloured compounds

• Act as catalysts (e.g. copper can speed up Zinc + Sulfuric Acid reaction)

• Good thermal and electrical conductors

• Shiny when polished (retain it unlike Group 1)

• Stronger and Harder

• Low reactivity

• High density

• Boiling/Melting points higher than Group 1

Before discovering protons, neutrons and electrons, scientists tried to classify the elements by arranging them in order of their atomic weights (i.e. relative atomic mass) The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed. Newlands found the 'Law of Octaves' as the properties seemed to repeat every 8th element Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights. Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct.

• No gaps

• More elements

• Actinide and Lanthanide section

• Noble gases

• D-block of Transition metals

• Mendeleev had some boxes with 2 elements in

Substance made from 2 or more elements chemically bonded together with a fixed proportion Can only be separated by chemical reaction

More than one substance NOT CHEMICALLY BONDED with any proportions Can be separated through: Filtration, Evaporation, Crystallisation, Distillation, Chromatography

A solution in which no more solid can dissolve at that temperature

High m.p. and b.p. Thermal and electrical conductor Shiny when polished Can be hammered into shape Ionically bonds with non-metals Metallically bonds with metal Metal oxides are basic

Low Thermal and electrical insulator Dull Brittle as solids Ionically bonds with metals Covalently bonds with non-metals Non-metal oxides are acidic

Filtration - solid: residue, liquid: filtrate

Evaporation or Crystallisation for solid Simple Distillation for solvent (see image)

Chromatography

Fractional Distillation (see image)

Separating Funnel

• Polar solvents (e.g., water) can dissolve ions and polar molecules

• Organic solvents (e.g., alcohols, cyclohexane) are useful for non-polar substances

1. Add warm water to dissolve the NaCl as it is soluble and stir to ensure fully dissolved

2. Filter the sand out using filter funnel, paper and flask

3. Add extra water to ensure all solution has gone through (wash through)

4. Dry the sand in an oven

5. Evaporate the water out by heating gently with a Bunsen burner in an evaporating basin. Heat to the point of crystallisation/to the point is starts bubbling to leave water of crystallisation

6. Leave to allow crystals to form slowly for at least 24 hrs

7. Pat dry the crystals

Electrostatic attraction between positive and negative ions

Electrostatic force of attraction between the nuclei and shared electrons (non-metals only)

Electrostatic attraction between positive metal ion and delocalised electrons

Giant Ionic lattice Simple molecular Giant covalent lattice, e.g., diamond, graphite, silicon, silicon dioxide Giant metallic lattice

High - lots of energy needed to break lots of ionic bonds

solid: non-conductor liquid/aqueous: conductor

Very High - lots of energy needed to break lots of covalent bonds

Non-conductor (no ions and no delocalised e-)

Low - little energy needed to overcome weak intermolecular forces

Non-conductor (except graphite)

High - lots of energy needed to break lots of metallic bonds

Conductor (delocalised e-)

Polymers contain very large molecules with covalent bonds. Thermosoftening polymers soften or melt when heated as the molecules are not joined together (intermolecular forces are strong enough due to large molecules to keep them solid at room temperature)

Pure metals are malleable as the metallic lattice has layers of atoms which can slide over each other Alloys are not as they have other elements of different sizes which distort the layers so they can't slide over each other

Graphite Diamond Graphene Fullerenes Carbon nanotubes

Giant covalent lattice bonded in flat layers (hexagons) which are weakly attracted to each other. Each carbon is bonded to 3 others, leaving a delocalised outer shell e- on each atom free to move along the layers

Very high

Soft (layers slide over with weak intermolecular forces)

✔

Electrodes as they are unreactive, cheap, can withstand high temperatures, is a conductor Pencil

Giant covalent lattice where each carbon is bonded to 4 others in a tetrahedral arrangement

Very high

Very hard

✘

Jewellery Drill bits + saw tips

Very high

Giant covalent lattice - one layer of graphite (one atom thick) Each carbon is bonded to 3 others, leaving a delocalised outer shell e- on each atom free to move along the layers

Simple molecule. Has a spherical shape with hexagonal or pentagonal rings. Hollow at the centre of the molecule. Each carbon is bonded to 3 others, leaving a delocalised outer shell e- on each atom but e- cannot move between molecules

✘

Delivery of drugs (hollow part) Lubricants in metal as it can roll Catalysts

Giant covalent lattice Very high length Tubes of graphene sheets. Each carbon is bonded to 3 others, leaving a delocalised outer shell e- on each atom free to move along the tube

Very high

High tensile strength + very hard

✔

Reinforce tennis racquets + golf clubs

Behave differently as the increased surface area: volume ratio means that there are more particles on the surface which can react, and they tend to clump together.

• Fuel cells require platinum as a catalyst so to lower costs, platinum nanoparticles are being used

• Delivery of drugs - Gold nanoparticles are used to reduce the amount of the drug needed and reduce side effects of the drug by delivering them to specific cells.

• Sun creams - Nanoparticles of Titanium dioxide and Zinc oxide are used to absorb harmful UV radiation and are clear and colourless, and give better skin coverage

• Synthetic skin - Nanoparticles (e.g., carbon nanotubes) are being used to create better synthetic skin that is stronger and more flexible (and maybe sense touch and heat)

• Cosmetics - In face creams in emulsions that contain vitamins, In moisturisers to kill bacteria, In foundations to diffuse light to partially disguise wrinkles Deodorants - Silver nanoparticles kill bacteria to prevent odour Electronics - Used to make smaller components

Nanoparticles may penetrate cell membranes to enter cells and cause DNA damage which can cause mutation and increase risk of cancer

Shows the electron structure of the ions

Can give impression that the structure is only pairs of ions

Very easy to draw

• Can give impression that structure is limited to a few ions

• Only shows 2D structure

Helps show how the ions are arranged relative to each other

Can give impression that structure is limited to a few ions

Gives good representation of how the ions are packed together

• May look like covalent bonds

• May look that ions are a long way apart

Sum of the relative atomic masses of all the atoms in the formula - Mr

6.02 × 10²³

Total mass of reactants = total mass of products (prove using relative formula masses). NB: any 'missing' mass is the mass of gas (not weighed) which has escaped into the air

A reaction where heat causes a substance to break down into simpler substances CaCO₃ → CaO + CO₂

When the amount of a reactant is greater than the amount that can react (ensures all of the other reactant is used up)

The reactant in a reaction that determines the amount of products formed. Any other reagents are in excess and will not all react

Amount (n,mol)= Mass (m,g)/Molar mass (M,g/mol)

Molar mass is just the relative formula mass (Mr)

Number of moles (mol) = Concentration (mol⁄dm³ ) × Volume (dm³)

Volume = Moles × 24

% yield= experimental yield (mol or g)/theoretical yield (mol or g)×100

% Atom economy= Total Mr of useful products/Total Mr of all reactants×100

Use a volumetric pipette with pipette filler to measure your acid or alkali and place into conical flask Add indicator (methyl orange or phenolphthalein) The other solution, acid or alkali is added to the burette using a filter funnel The solution is added from the burette into the conical flask until the indicator changes colour (end point). This is your first rough titre. The next titres will be added drop-wise around the point where the indicator changed colour in your rough titre Repeat until concordant results are found - 0.1cm³ close to each other and find a mean of the 2 concordant results

Add drop-wise near to the endpoint Repeat and calculate a mean Have a white tile under the flask Swirl the solution

Acid: Red Alkali: Yellow End point: Peach/Orange

Acid: Colourless Alkali: Pink End point: [Colour of whichever substance you're adding]