Chemistry

Chemistry

1. History of the Atom

   • John Dalton described atoms as indestructible and all atoms of given elements are identical
   • Not all atoms of an element are identical as atoms of the same element can have different numbers of neutrons
   • JJ Thompson discovered the electron and created the plum pudding model of an atom
   • JJ Thompson thought that electrons were surrounded by a positively charged soup which balanced out the negative charge
   • Rutherford carried out the Gold Foil Test, which proved that there was a nucleus in the centre of the atom and was orbited by electrons
   • Bohr's experiment was the same as Rutherfords as the worked together on it
   • Bohr discovered that you can have more electrons in the outer shell than in the inner shell
   • Chadwick discovered the neutron, which helps to neutralise the protons and electrons. it was difficult to detect as there was no charge being emitted

2. Isotopes

   • Atoms of the same element always have the same atomic number/number of protons
   • Isotopes are atoms of the same element with the same number of protons and electrons but a different number of neutrons
   • When an atom loses a neutron it has physical differences - its density changes but because the number of electrons hasn't changed the chemical properties are the same

3. Ions

   • Ions are electrically charged particles. They can be single particles or a group of particles
   • Metal atoms lose electrons to form positive ions and non-metal atoms gain electrons to form a negative ion.
   • The number of electrons gained or lost is the same as the charge of the ion. Chlorine atoms gain 1 electron to become Cl- when oxygen atoms gain 2 electrons to become O2-.
   • Atoms with a full outer shell (8 electrons) are stable
   • An ionic compound is a chemical compound that consists of ions that are bonded electrically. Overall these compounds are neutral
   • Lithium + Sulfur = Lithium Sulphide Calcium + Carbon = Calcium Carbonate Potassium + Nitrogen = Potassium Nitrate
   • Ionic compounds are giant structures of ion, held together in a lattice by electrostatic forces known as ionic bonds
   • Ionic Compounds
     • An Ionic compound is a giant structure of ions
     • they have a regular repeating pattern called a giant ionic lattice
     • They are bonded by an electrostatic charge
     • Ionic compounds are solids at room temperature
     • Some ionic compounds are soluble in water
     • Some ionic compounds don't conduct electricity but do in water
     • They don't conduct electricity in ethanol
     • They have a high melting and boiling point
     • Increased amount of kinetic energy can overcome the bonds
     • Some are overcome in melting but all are overcome in boiling
     • They conduct electricity in solution
     • They contain charged particles
     • Water molecules have charges which pull the cation and anion apart
     • Anion = Negative Ion Cation = Positive Ion
       • TIP TO REMEMBER Anion = Negative Ion A Negative ION 

4. Reactivity Groups 1 and 7

   • Group 1
     • Group 1 metals react by losing an electron
     • Reactivity increases as the atoms get bigger down the group
     • The bigger the atom the harder is is to hold onto the last electron on the outer shell
     • This is because the bigger distance between the nucleus and electron, the weaker the electrostatic force
     • It also happens because the inner shells block the force
   • Group 7
     • Group 7 metals react by gaining 1 electron
     • The reactivity decreases as the atoms get bigger down he group
     • The fewer shells there are the closer the outer shell is to the nucleus, making the electrostatic force stronger

5. Covalent Bonding

   • The covalent bonds are formed when 2 atoms of non-metal elements share a pair of electrons so that they can have a full outer shell
   • The atoms are held together by the electrostatic attraction between positive charges on their nuclei and negative charges on their shared electrons
   • The electron arrangement is then like the nearest noble gas
   • Most of the compounds of non-metals with non-metals have simple molecular structures although form giant covalent structures
   • Giant Covalent Structures
     • Atoms that share electrons can form giant covalent structures or macromolecules
     • Diamond, Graphite and Silicon Dioxide are examples of giant covalent structures
     • All atoms in these structures link to each other via strong covalent bonds which means they have a very high melting point
     • Allotropes are forms of an element that exist in the same state but have different properties
     • Diamond, Graphite and fullerenes are all allotropes of carbon

6. Hydrocarbons

   • A hydrocarbon is a compound made from carbon and hydrogen atoms only
   • Most of the hydrocarbons in crude oil are saturated hydrocarbons called alkenes
   • Saturated means that all the carbon - carbon bonds are single covalent bonds
   • The Homologuos series is a series of compounds that have the same general formula but different lengths

7. Fractional Distillation

   • The hydrocarbons are separated into factions with similar numbers of carbon atoms
   • The column is hot at the top and cold at the bottom
   • The oil is heated
   • This process is called fractional distillation
   • - Boiling point increases - Viscosity increases -Flammability decreases - Volatility decreases

8. Alkenes

   • Alkenes react with hydrogen, water and halogens by the addition of atoms across the C=C double bond so that the C=C becomes a C-C
   • Hydrogenation is the addition of hydrogen to an alkene in the presence of a nickel catalyst to produce a corresponding alkene
   • Hydration is the addition of water to an alkene that takes place by reaction with steam in the presence of a catalyst and high temperature to produce an alcohol
   • The addition of a halogen to an alkene to produce a saturated hydro
   • Alkenes react with bromine waterm turning it from orange to colourless. Bromine water tests for the presence of unsaturated compounds

9. Alcohols

   • A functional group determines how a group of compounds will typically react
   • Alcohols form a homologuos series that contain the function group OH (Hydroxyl Group)
   • Alcohols are flammable. They burn in air to produce Carbon Dioxide and Water
   • Short chain alcohols have relatively low boiling points as they have weaker intermolecular forces
   • They dissolve completely to form a neutral solution
   • They can be oxidised to form carboxylic acids
   • Ethanol is the main alcohol in alcoholic drinks. It is not as toxic as methanol but still damages the liver and brain
   • Methylated spirits are a poisonous mix of ethanol and methanol and is used as fuel

10. Carboxylic Acids

    • In the presence of an oxidising agent alcohols are oxidised to form carboxylic acids
    • During the reaction the potassium diochromate turns from orange to green
    • Esters
      • Esters have a functional group of COO
      • Produced during an esterification reaction between an alcohol and a carboxylic acid.
      • An esterification reaction is also a condensation reaction and water is released
      • Esters are volatile compounds
      • They have distinctive smells and are used as flavourings and perfume
      • Small chain esters dissolve in water. They have a Ph close to neutral

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