Chemistry
- Created by: AOconnor
- Created on: 13-05-18 13:32
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- Chemistry
- Separating Mixtures
- Filtration separates soluble solids from insoluble solids by dissolving and filtering
- Crystallisation obtains a soluble solid from a solution
- Mixture is warmed then water evaporates, leaving solid
- Distillation obtains solvent from solution via evaporation and condensation
- Fractional distillation separates mixtures containing components with different boiling points
- Chromatography separates the different soluble coloured components of a mixture
- Periodic Table
- Development
- Newlands arranged via atomic weight, so some were in the wrong place
- Mendeleev left gaps to allow discovery
- Organised via increaseing atomic number
- Each element was in a group with others that had similar properties
- Group 0 (Noble gases)
- Full outer shell making them unreactive
- Group 1 (Alkali Metals)
- Low melting/boiling point that decrease down group
- Reactivity increases down group as electron can be lost more easily
- React vigorously so kept in oil
- When reacting with water, metal hydroxide is formed and hydrogen released
- When hydroxide dissolves, alkaline solution produced
- Low density (float on water)
- Group 7 (Halogens)
- Reactivity increases down group (harder to gain electron)
- React with metals to produce ionic salts
- More reactive halogens displace less reactive ones
- Reactivity increases down group (harder to gain electron)
- Development
- Atoms
- Isotopes have the same number of protons but different neutrons
- Ions form when an atom loses/gains electrons
- Plum Pudding
- Atoms contained tiny, negative electrons surrounded by sea of positive charge
- Disproved when scientists fired alpha particles at sheet of gold
- Most passed through but some deflected back
- Meant that the positive charge was concentrated in a small area
- Most passed through but some deflected back
- Ionic compounds
- Transfer of electrons from metal to non-metal
- Ionic bond is strong electrostatic attraction between positive and negative ions
- Properies
- High melting/boiling point (ionic bonds are hard to overcome)
- Only conduct electricity when aqueous or molten
- Covalent Compounds
- Shared pair of electrons between atoms (2 non-metal)
- Strong covalent bonds
- Small molecules
- Small number of atoms joined via covalent bond
- Weak intermolecular forces (low melting point)
- Larger the molecule, stronger the intermolecular forces
- Giant structures
- Strong covalent bonds (high melting point)
- Diamond
- Giant rigid structure (lattice)
- 1 carbon joins 4 other carbons)
- Strong bonds means high melting point
- No charged particles so doesn't conduct electricity
- Giant rigid structure (lattice)
- Graphite
- High melting point and giant lattice
- 1 carbon joins 3 others (layered hexagonal structure)
- Weak intermolecular forces between layers causes sliding
- 1 electron is delocalised and can carry charge around structure
- Conducts electricity
- 1 carbon joins 3 others (layered hexagonal structure)
- High melting point and giant lattice
- Silicon dioxide
- Similar to diamond
- 1 oxygen joined to 2 silicon
- 1 silicon joined to 4 oxygen
- Similar to diamond
- Separating Mixtures
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