Chemistry (C2)

Nota:

• Elements react to form compounds by gaining, sharing or losing electrons.
• Elements react to form compounds by gaining, sharing or losing electrons.
• The element is ALWAYS trying to get to a noble gas configuration.
• Atoms involved in chemical bonding are in the OUTER SHELL.

Nota:

• Held together by strong forces between the oppositely charged ions.
• -Gaining or losing electrons. -When a non-metal and metal react.

1. Characteristics

   Nota:

   • -Giant structure (or latice) -High melting and boiling point. -Hard and Brittle. -Conduct electricity in water.
   1. High melting and boiling points

      Nota:

      • High temperature required to break the positive and negative attraction.
   2. Conductors

      Nota:

      • In water, dissociated ions are free to conduct an electric charge.
      • MOLTEN ionic compounds (salts) also conduct electricity.
2. Representation

   Nota:

   • Ionic bonding can be shown by: dot and cross diagrams.
   1. Example

Nota:

• The charges on the ions in an ionic compound always cancel each other out.

1. Brackets

   Nota:

   • Used when we need to multiply ions. An example of this is:  Ca(OH)₂ - Need two hydroxide ions.

Nota:

• Sharing electrons
• -Sharing electrons -When two non-metals react.
• Substances containing covalent bonds consist of simple molecules, but some have giant covalent structures.

1. Characteristics

   Nota:

   • -Low melting and boiling points. -Don't conduct electricity well.
   1. Low melting and boiling points

      Nota:

      • Weak intermolecular forces break down easily.
   2. Conductors

      Nota:

      • They do not have free electrons or an overall electrical charge.
2. Representation

   Nota:

   • We can use dots and crosses to show where the electrons are shared, on each atom.
   1. Example

Nota:

• The atoms in metals are: -CLOSELY packed together. -Arranged in REGULAR layers.

1. Higher tier

   Nota:

   • -Electrons in the highest energy level are delocalized. -They can move FREELY. -Produces a lattice of positive ions in a 'sea' of moving electrons -The DELOCALISED ELECTRONS strongly attract the positive ions and hold the giant structure together.
2. Characteristics

   Nota:

   • -Good conductors of heat and electricity. -Malleable -Ductile
   1. Conductors

      Nota:

      • Free electrons carry heat or carry a charge throughout the metal.
   2. Malleable and ductile

      Nota:

      • Free electrons allow metal atoms to slide over each other.

Nota:

• -Strong electrostatic forces hold ions together. -Solids at room temperature. -High melting and boiling points

1. Melting

   Nota:

   • -MELTING = free electrons/ions -Allows them to carry electrical charge. -Therefore conduct electricity.
2. Dissolving

   Nota:

   • -Some ionic structures dissolve in water. -Water molecules can split up the lattice. -Ions are free to move therefore conduct electricity.

Nota:

• -Held together by strong covalent bonds. -ONLY act between atoms of molecule. -Low melting and boiling points. -No electricity conduction.

1. Intermolecular forces (H)

   Nota:

   • -Intermolecular forces are the forces of ATTRACTION. -Broken when boiled or melted. -Small molecules (H₂, CH₄) have weakest intermolecular forces, thus they are gases at RT. -Larger molecules (Br₂) have stronger attractions, so may be liquids at room temperature. -I₂ is a solid at room temperature.

Nota:

• -Atoms of some elements can form several covalent bonds. -Atoms can join together to make GCS's (macromolecules). -Every atom joined to several other atoms (STRONG bonds). -Therefore, VERY high melting point.

1. Diamond

   Nota:

   • -Form of carbon that has a regular 3-D giant structure. -Each carbon atom covalently bonded to four others. -Makes diamond hard and transparent. -Silicon dioxide IS SIMILAR.
2. Graphite

   Nota:

   • -Form of carbon (2-D layers) -One carbon atom is covalently bonded to three others. -No covalent bonds between layers, so they slide over each other. -Graphite is slippery and grey.
   • -One electron from each carbon atom is delocalised. -Allows graphite to conduct heat and electricity. -Weak intermolecular forces between layers in graphite, meaning layers can slide over each other easily.
3. Fullerenes

   Nota:

   • -Large molecules from hexagonal rings of carbon. -Rings join together to form cage-like shapes with different numbers of carbon atoms (some are NANO-SIZED).

Nota:

• When we bend and shape metals, the layers of atoms in the giant metallic structure slide over each other.

1. Alloys

   Nota:

   • -Mixtures of metals or metals mixed with other elements. -Different sized atoms distort layers in metal structure therefore difficult for them to slide. -Alloys are harder than pure metals.
   1. Shape memory alloys

      Nota:

      • -Bent or deformed into a different shape. -When heated, they return to original shape. -Used for many things: e.g. dental braces.
2. Metal structures

   Nota:

   • -Delocalised electrons (move throughout the giant metallic lattice and transfer energy quickly). -Good conductors of heat and electricity.

Nota:

• Depends on the monomers used to make them.  Could also depend on the reaction conditions.

1. Poly(ethene)

   Nota:

   • Low density (LD) poly(ethene) and high density (HD) poly(ethene) are made using different catalysists and different reaction conditions.
   • Changing reaction conditions can also change the properties of the polymer that is produced.
2. Thermosoftening polymers

   Nota:

   • -Poly(ethene) is an example. -Made up of individual polymer chains that are tangled together. -Heated - soft. -Cooled - hard. -Can be heated to mould into shapes and remoulded through heating again.
   • -Forces between polymer chains are weak. -When heated, these weak intermolecular forces are broken and polymer becomes soft. -When cooling down, intermolecular forces bring polymer molecules back together, thus hardening polymer.
3. Thermosetting polymers

   Nota:

   • -Do not melt or soften when heated. -Polymers set hard when first moulded. -Due to strong covalent bonds forming cross-links between their polymer chains. -Strong bonds hold polymer chains in position.

Nota:

• The study of small particles that are between 1 and 100 nanometres in size.

1. Nanoparticles

   Nota:

   • -1 nanometre is 10−⁹m. -Very small sizes give them: --BIG surface area. --New properties which make them very useful materials.
2. Nantechnology

   Nota:

   • Uses nanoparticles to: --Highly selective sensors. --Very efficient catalysts. --New coatings. --New cosmetics. --Improvement in construction materials.
3. The Future

   Nota:

   • -VERY EXCITING. -Unpredictable consequences for our health and the environment. -MORE research needed to find out effects.

Nota:

• Protons - 1 Neutrons - 1 Electrons - 0

1. Mass number

   Nota:

   • Total number of protons and neutrons.
2. Atomic number

   Nota:

   • (Or the proton number) The number of protons and electrons in an atom.
3. Isotopes

   Nota:

   • Atoms of the same element with DIFFERENT numbers of NEUTRONS.

Nota:

• We use relative atomic masses to compare the masses of atoms.

1. Relative atomic mass

   Nota:

   • Relative atomic mass (Ar) is an average value that depends on the isotopes the element contains.
2. Relative formula mass

   Nota:

   • (Mr) Adding up all the relative atomic masses of the atoms in its formula.
3. Moles

   Nota:

   • One mole of a substance is its relative formula mass in grams.

1. Percentage composition

   Nota:

   • Divide the relative atomic mass of the element by the relative formula mass of the compound then multiply by 100.
   1. Example

      Nota:

      • Percentage of C in CO₂: C = 12 , O = 16 Mr of CO₂ is: 12 + 32 = 44 So: 12/44 x 100 = 27.3%
2. Empirical formula

   Nota:

   • Simplest ratio of atoms or ions in a compound.
   • To work out: -Mass in 100g -Mass / Ar -Divide by smallest (mass/Ar) -Convert to Empirical formula -REMEMBER: You can't have a decimal of an atom, so convert to integers.
   1. Example

      Nota:

      • Empirical formula of the hydrocarbon that contains 80% C -Mass in 100g (C=80 , H=20) -Mass/Ar (C=80/12=6.67 , H=20/1=20) -Smallest ratio (C=6.67/6.67 = 1 , H=20/6.67=3) -Empirical formula is CH₃
3. Molecular formula

   Nota:

   • -Empirical formula not always the same as molecular formula in covalent compounds. -e.g. Ethane's molecular formula is: C₂H₆ BUT its empirical formula is CH₃

Nota:

• To work out: -Calculate Mr for all compounds. -Work out how much the product weighs. -(The amount you have / mole amount) x Mr of thing you are trying to work out 

Nota:

• The yield of a chemical reaction describes how much product is made.
• The percentage yield tells us how much product is made compared with the maximum amount that could be made.

1. Formula

   Nota:

   • Formula for Percentage Yield: (amount of product collected / maximum amount of product possible) x 100
2. Why?

   Nota:

   • It isn't possible to collect the amounts calculated from the chemical equation because: -Incomplete reaction -Other reactions may happen. -Product may be lost when it is seperated or collected from the apparatus. 
3. High yields

   Nota:

   • Good for industry as it: -Conserves resources -Reduces waste.
   • Chemical processes should also waste as little energy as possible so that: -There is a reduction in pollution. -It makes production more sustainable. 

Nota:

• In a reversible reaction, the products of the reaction can react to make the original reactants.
• Reversible reactions are shown by this sign: ⇌

1. Example

   Nota:

   • Ammonium chloride ⇌ ammonia + hydrogen chloride

Nota:

• The process whereby small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper.

1. Paper Chromotography

   Nota:

   • Used to identify food additives, such as artificial colours. 
   • The process: -A spot of colour is put onto paper and a solvent can move through it. -The colours move different distances depending on their solubility. 
2. Gas Chromotography

   Nota:

   • Used to separate mixtures so that compounds can be identified.
   • The process: -Mixture is carried by a gas through a long column packed with particles of a solid. -Individual compounds travel at different speeds and come out at different times. -Amount of substance leaving column at different times is recorded against time and shows: --Number of compounds --Retention times
   1. Mass spectrometer

      Nota:

      • This is connected to the gas chromatography column to give further data.
      1. Relative molecular masses

         Nota:

         • A GC-MS can give the relative molecular mass of a compound. It can do this by reading off the molecular ion peak, which is furthest to the right on the mass spectrum. 

Nota:

• Measures the speed of a reaction or how fast it is.

1. Equation

   Nota:

   • Rate of reaction = amount of reactant used / time  
   • Rate of reaction = amount of product formed / time
2. Gradient

   Nota:

   • The gradient of the line on a graph of amount of reactant or product against time tells us the reaction at that time. The steeper the gradient. the faster the reaction.
   • The faster the rate, the shorter the time it takes for the reaction to finish. So rate is INVERSELY PROPORTIONAL to time. 

Nota:

• -Reactions can only happen if particles collide. -Particles must collide with enough energy to create new substances. -This minimum energy is called the activation energy.
• IMPORTANT to learn each node word by word.

1. The effect of temperature

   Nota:

   • Increasing the temperature increases the kinetic energy of particles therefore they will collide more frequently with enough activation energy and so the rate of reaction will increase.  
   • A rise of 10°C will roughly double the rate of many reactions, so they go twice as fast.
2. The effect of surface area

   Nota:

   • The rate of a chemical reaction increases if the surface area of any solid reactant is increased. This increases the frequency of collisions between reacting particles.
3. The effect of catalysts

   Nota:

   • -Catalysts change the rates of chemical reactions. -Catalysts that speed up reactions lower the activation energy required, therefore more successful collision occur.
   • Catalysts do not get used up during a chemical reaction.
   • Different catalysts are needed for different reactions.
4. The effect of concentration

   Nota:

   • Increasing concentration increases the frequency of successful collisions (these are the ones with the activation energy). This therefore will increase the rate of reaction.
5. The effect of pressure

   Nota:

   • Increasing pressure increases the frequency of collisions because particles are closer together since they occupy a smaller volume. This will increase the frequency of collisions with enough activation energy and so increases the rate of reaction. 

Nota:

• -Catalysts are used in industry to increase the rate of reactions and reduce energy costs. -This means that less fossil fuels are burned. therefore conserving resourcing and reducing pollution

1. Traditional catalysts

   Nota:

   • Often transition metals or their compounds. However, some of these are toxic and may cause harm to the environment. 
2. Modern catalysts

   Nota:

   • Being developed in industry which result in less waste and are safer for the environment. 

Nota:

• In a reaction, energy may be transferred to or from the reacting substances.

1. Exothermic

   Nota:

   • Reactions that transfer energy to the surroundings.
   1. Examples

      Nota:

      • -Combustion (burning fuels) -Oxidation reactions (respiration) -Neutralization reactions (involving acids and bases)
   2. Uses

      Nota:

      • Used in hand warmers and self-heating cans.
2. Endothermic

   Nota:

   • Reactions which take in energy from the surroundings.
   1. Examples

      Nota:

      • Some cause a decrease in temperature and others require a supply of energy.
      • Solid compounds that are mixed with water cause temperature decrease because endothermic changes happen as they dissolve
      • Thermal decomposition reactions need to be heated continuously to keep the reaction going.
   2. Uses

      Nota:

      • Used in instant cold packs for sports injuries.

Nota:

• In reversible reactions, the reaction in one direction is exothermic and in the other, endothermic.

1. Example

   Nota:

   • Hydrated copper sulfate ⇌ anhydrous copper sulfate CuSO₄⋅5H₂O ⇌ CuSO₄ + 5H₂O
   • The hydrated copper sulfate must be heated continuously for the reaction to complete, because it is an endothermic reaction.
   • Adding water to the anhydrous copper sulfate causes the mixture to get hot, because it is an exothermic reaction.

Nota:

• Acids are substances that produce H⁺(aq) ions, when they are added to water.
• Alkalis are bases that dissolve in water to make alkaline solutions. They produce OH⁻ ions.

1. Bases

   Nota:

   • React with acids and neutralizes them. 
2. pH scale

   Nota:

   • Potential Hydrogen scale - it shows how acidic or alkaline a solution is. 

Nota:

• Acids will react with metals that are above hydrogen in the reactivity series.

1. Equation

   Nota:

   • Acid + Base → Salt + Hydrogen
   • When this happens, a neutralisation reaction take place.
2. Crystals

   Nota:

   • Salts can be crystalllised from solutions by evaporating off water.
3. Examples

   Nota:

   • HCl → Chlorides HNO₃ → Nitrates H₂SO₄ → Sulfates

Nota:

• We can make soluble salts by: Acid + Alkali → Salt + Water

1. Neutralisation

   Nota:

   • H⁺(aq) + OH⁻(aq) → H₂I(l)
2. Insoluble salts

   Nota:

   • Mixing solutions of soluble salts that contain the ions needed, in order to form a precipitate (insoluble salt).
3. Precipitation

   Nota:

   • An important way of removing some metal ions from industrial waste water.

Nota:

• -Electricity is used to break down ionic compounds into elements. -When electricity is passed through molten ionic compounds or a solution containing ions, electrolysis takes place. -Substance broken down is an electrolyte.

1. Electrodes

   Nota:

   • -Made of an inert substance that doesn't react with the products. -Ions which move to either electrode are discharged to produce elements.
   1. Anode

      Nota:

      • Negatively charged ions are attracted to the anode, losing their charge and forming non-metallic elements.
   2. Cathode

      Nota:

      • Positively charged ions are attracted to the cathode, losing their charge and forming either hydrogen or metals, depending on the electrolyte. 

Nota:

• When an ion reaches an electrode, they lose or gain electrons to become neutral atoms. 

1. OILRIG

   Nota:

   • Oxidation  Is  Loss Reduction Is Gain
   1. Oxidation

      Nota:

      • Negative ions lose electrons to become neutral atoms, with some non-metals forming molecules. 
   2. Reduction

      Nota:

      • Positive ions gain electrons.
2. Half equations

   Nota:

   • Anode: 2Br⁻ → Br₂ + 2e⁻ Cathode: Pb²⁺ + 2e⁻ → Pb Anode - Losing electrons. Cathode - Gaining electrons.
3. Aqueous solutions

   Nota:

   • Water contains hydrogen and hydroxide ions.
   1. Negative electrode

      Nota:

      • Hydrogen may be produced at the negative electrode if the positive ions in the solution are those of a metal more reactive than hydrogen. 
   2. Positive electrode

      Nota:

      • Oxygen is usually produced. If the solution has a high concentration of a halide ion, then a halogen will be produced.

Nota:

• Aluminium oxide is electrolysed, because aluminium is more reactive than carbon. We do this to manufacture aluminium.

1. Cryolite

   Nota:

   • Added to aluminium oxide to reduce the melting temperature (from 2000°C to 850°C)
2. Electrodes

   Nota:

   • Different products are formed at either electrode.
   1. Anode

      Nota:

      • Oxide ions are oxidised to oxygen atoms by losing electrons and these oxygen atoms form oxygen molecules.
      1. Substances

         Nota:

         • -Anode is made of carbon. -At high temperatures, the oxygen reacts with the carbon to form carbon dioxide. -All the carbon electrodes gradually burn away, therefore they must be replaced regularly. 
   2. Cathode

      Nota:

      • Aluminium ions are reduced to aluminium atoms by gaining electrons. The molten aluminium is collected from the bottom of the cell.

Nota:

• Brine is a solution of sodium chloride in water.

1. Brine ions

   Nota:

   • Brine contains: -Na⁺ sodium ions -H⁺ hydrogen ions -Cl⁻ chloride ions -OH⁻ hydroxide ions
2. Electrodes
   1. Anode

      Nota:

      • Chlorine is produced from the chlorine ions. 2Cl⁻ → Cl₂ + 2e⁻ 
   2. Cathode

      Nota:

      • Hydrogen ions. 2H⁺ + 2e⁻ → H₂
   3. Leaving

      Nota:

      • A solution of sodium ions and hydroxide ions.
3. Products

   Nota:

   • Sodium hydroxide is a strong alkali and has many uses: -Soap -Paper -Bleach -Neutralising acids -Controlling pH
   • Chlorine is used to: -Kill bacteria in drinking water and swimming pools. -Make bleach. -Make disinfectant. -Make plastics.
   • Hydrogen is used to: -Make margarine. -Make hydrochloric acid.

Nota:

• Uses electrolysis to put a thin coating of metal onto an object. 

1. Uses

   Nota:

   • Electroplating is used to: -Make the object look more attractive. -Protect a metal object from corroding. -Increase the hardness of a surface. -Reduce costs by using a thin layer rather than pure metal.
2. Process

   Nota:

   • Object to be electroplated is made the negative electrode. 
   1. Electrolyte

      Nota:

      • A solution containing ions of the plating metal. 
   2. Electrodes
      1. Anode

         Nota:

         • -Made from the plating metal. -Atoms of the plating metal lose electrons to form metal ions which go into the solution.
      2. Cathode

         Nota:

         • Metal ions from the solution gain electrons to form metal atoms which are deposited on the the object to be plated.