Chem Paper 1

• Relative masses, charges of subatomic particles

  Proton: 1, +1

  Neutron: 1, 0

  Electron: Negligible, -1
• Relative Atomic Mass definition

  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
• Relative Atomic Mass formula

  ((mass no.1×%abundance)+(mass no.2×%abundance)+⋯)/100
• History of the atom

  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, butsome 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.
• What would have happened in Rutherford's experiments if the Plum pudding model were correct

  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.
• Plum pudding model vs Nuclear model

  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 vs Atomic number

  Atomic mass: The sum of protons and neutrons (bottom)

  Atomic number: a unique number of protons = electrons (if atom) (top)
• How is the periodic table arranged?

  by increasing atomic number

  in groups of similar properties (occur at relative intervals - periodicity), and valency

  in periods of occupied electron shells
• Relative atomic mass formula

  RAM = (Mass no x abundance) + (Mass no. x abundance) / 100
• Ions of metals


  positive
• Ions of non-metals


  negative
• Properties and Trends for Noble Gases/Group 0 (Appearance, Reactivity, Compound properties, Boiling/Melting points, density)

  - 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
• Properties and Trends for Alkali Metals/Group 1 (Appearance, Reactivity (+water reaction), Compound properties, Boiling/Melting points, density)


  - 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)
• Group 1 reaction with oxygen (specifically first 3) and description

  4[Alkali metal](s) + O₂(g) -> 2[Alkali metal]₂O(s)

  The metals burn with different colour flames
• Group 1 reaction with water (specifically first 3) and description

  [Alkali metal](s) + 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
• Group 1 reaction with chlorine (specifically first 3) and description

  2[Alkali metal](s) + Cl₂(g) -> 2[Alkali metal]Cl(s)

  All burn in chlorine to form metal chlorides which are white powders
• Description of lithium reaction with water

  Fizzes, moves on the surface of the water
• Description of potassium reaction with water

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

  Explosive reaction
• Definition of sublimination


  When the melting and boiling points come together so liquid state is skipped
• Properties and Trends for Halogens/Group 7 (Appearance, Reactivity, Compound properties, Boiling/Melting points, density)

  - 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
• Halogen appearances - Fluorine, Chlorine, Bromine, Iodine

  Fluorine: pale yellow gas

  Chlorine: pale green gas

  Bromine: Dark brown liquid w/orange gas

  Iodine: grey solid (as a gas - 184°C - violet)
• Halides meaning


  Compounds made from Halogens
• Displacement reaction between Chlorine and Potassium iodide

  Cl₂ + 2KI -> 2KCl + I₂
• Properties and Trends for Transition metals (Appearance, Reactivity, Compound properties, Boiling/Melting points, density, Conductivity)

  - 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
• History of the Periodic Table

  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.
• Differences between Mendeleev's table and the modern one

  - No gaps

  - More elements

  - Actinide and Lanthanide section

  - Noble gases

  - D-block of Transition metals

  - Mendeleev had some boxes with 2 elements in
• Compound definition


  Substance made from 2 or more elements chemically bonded together with a fixed proportion

  Can only be separated by chemical reaction
• Mixture definition


  More than one substance NOT CHEMICALLY BONDED with any proportions

  Can be separated through: Filtration, Evaporation, Crystallisation, Distillation, Chromatography
• Saturated Solution definition


  A solution in which no more solid can dissolve at that temperature
• General properties of metals (Melting and boiling points, Conductivity, Appearance, Malleability, Bonding, Acid/base oxides)

  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
• General properties of non-metals (Melting and boiling points, Conductivity, Appearance, Malleability, Bonding, Acid/base oxides)

  Low

  Thermal and electrical insulator

  Dull

  Brittle as solids

  Ionically bonds with metals

  Covalently bonds with non-metals

  Non-metal oxides are acidic
• Method of separation for Insoluble solid and liquid

  Filtration - solid: residue, liquid: filtrate
• Method of separation for Soluble solid dissolved in a solvent

  Evaporation or Crystallisation for solid

  Simple Distillation for solvent (see image)
• Method of separation for Soluble solid


  sdissolved in solventChromatography
• Method of separation for Two miscible liquids (liquids that mix)

  Fractional Distillation (see image)
• Method of separation for Two immiscible liquids (liquids that don't mix)

  Separating Funnel
• 2 types of solvent

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

  - Organic solvents (e.g., alcohols, cyclohexane) are useful for non-polar substances
• Practical: separating rock salt to get pure NaCl & sand

  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
• Ionic bonding definition


  Electrostatic attraction between positive and negative ions