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Chemistry Section 1 (A (States of matter (Solids (Particles close together…

- - - - Particles close together
      - Arranged in a regular pattern
      - held together by strong forces of attraction
      - vibrate at a fixed position
      - cannot move from place to place
    - - close together
      - arranged randomly
      - can move around each other and take the shape of the container
      - forces of attraction keep particles close together
        
        but are weak enough to allow movement
    - - far apart
      - arranged randomly
      - move quickly in all directions
        
        brownian motion
      - forces of attraction very weak
    - - Solid and liquid
        
        melting
        
        particles get more energy and vibrate more
        
        vibrate fast enough to overcome forces of attraction
        
        they become free to move
        
        energy in, endothermic
        
        Freezing
        
        particles move less, less energy
        
        move slow enough for forces attraction to bring them close together
        
        energy out, exothermic
      - sublimation
        
        a few substances have the ability to go from gas to solid with no liquid state, eg CO2
- - - - Random movement of particles
        
        from area of high concentration to area of low concentration
      - Rate of difusion
        
        less dense particles diffuse faster
    - - material categories
        
        Molecule
        
        pure, neutral substance with 2 or more atoms chemically bonded
        
        element
        
        single, pure substance containing only 1 type of atom
        
        Compound
        
        single, pure substance containing 2 or more elements chemically combined
        
        mixture
        
        impure substance, containing 2 or more compounds/elements not chemically combined
      - insoluble solid in a liquid
        
        Filtration, Centrifuge, decanting
        
        remaining solid
        
        residue
        
        liquid
        
        filtrate
      - mixture of 2 solids
        
        uses difference in properties
        
        salt and sand
        
        solubility in water
        
        sugar and salt
        
        solubility in alcohol
        
        iron and sulfur
        
        magnetic property of iron
        
        uses dissolving in water, filtering, evaporating,to point of crystallisation, then crystallising, then drying
      - simple distillation
        
        solid dissolved in solvent
        
        solvent boils, and condenses in condenser
        
        solution becomes more concentrated and eventually crystallises
        
        anti bumping granules help water boil more smoothly
        
        position thermometer in equilibrium between liquid and gaseous state
        
        ensure condenser remains full of water, no air pockets, constant flow of coolant
      - fractional distillation
        
        uses difference in boiling points between liquids
        
        careful and slow heating causes evaporation of different liquids at different points, liquids can be collected
        
        Crude Oil
      - seperation funnel
        
        Used to separate 2 immiscible liquids
        
        the funnel, with the tap, seperates the liquids into 2 layers, which can then be decanted
        
        E.g oil and water
      - Chromatography
        
        uses solubility of different dyes
- - - - made up of only 1 type of atom
      - Atoms
        
        proton and neutron nucleus, electron shells
        
        Proton
        
        +1. Mass 1
        
        Neutron
        
        neutral. Mass 1
        
        electron
        
        -1. mass 1/1836
        
        electron arrangement
        
        electrons occupy a particular energy level, electrons at lowest energy level in innermost shells
        
        electrons in the same group have the same number of electrons in the highest energy level (outer shell)
        
        1st shell: 2 electrons
        
        2nd shell: 8 electrons
        
        3rd shell: appears full at 8, but can expand to 18
        
        Ions
        
        when atoms form chemical bonds they transfer electrons to complete their outer shell. They form ions.
        
        Atoms that lose electrons form + ions
        
        Number of protons > number of electrons
        
        cations
        
        Atoms that gain electrons form - ions
        
        number of protons < number of electrons
        
        anions
        
        charge of atom is neutral
        
        number of e = number of p
        
        number of protons: atomic number
        
        number of protons + number of neutrons = mass number
        
        atoms arranged in a periodic table by their atomic number
        
        .
        
        Isotopes
        
        elements all have atoms of the same number of protons/ electrons
        
        but they can have variations in number of neutrons
        
        These are isotopes
        
        examples: Carbon-12, Carbon-14. Hydrogen-1, Deuterium (H-2) Tritium (H-3)
        
        They have different physical properties, such as radioactivity ( C-14 and H-3), but share the same chemical properties
        
        Relative mass
        
        the standard measurement for all atoms and molecules
        
        Standard mass: C-12
        
        relative mass allows for particles to be easily compared
        
        Relative atomic mass (Ar)
        
        Taken from the standard where C-12 is exactly 12 units
        
        Calculating Ar
        
        calculated using the masses and the relative abundance of an isotope.
        
        [ (%IsotopeA x massA) + (%IsotopeB x massB)] /100
        
        the weighted avg mass takes into account of the contribution made by each isotope
      - periodic table
        
        Groups: group number shows number of electrons in outer shell (except group 0 - full outer shell)
        
        periods
        
        period number shows the number of energy levels present (i.e number of shells)
- - - - Mr is relative formula mass, it is the mass of a molecule.
      - Its calculation is (number of that element in the molecule x relative atomic mass) + (number of that element in the molecule x relative atomic mass)
    - - Ar is relative atomic mass, it is the average mass of an atom of a specific element.
      - It is calculated by doing (% of isotope x mass of isotope) + (% of isotope x mass of isotope) over 100.
    - - A mole is an amount, in the same way that you can have a dozen buns, you can have a mole of carbon.
      - Having a mole of something is having 6.022x1023 of it.
      - A mole is Avogadro's number simpy because if you have 1 mole of an element its weight in grams will be its atomic mass.
- - - - Weigh you compound, remove one element of the compound through a reaction (break up a metal oxide or salts), then weigh again.
      - The first weight is AB the second weight is A so doing AB-A= B.
      - Now that you have the weight of A and B you can work out the formulae by doing the weight divided by the Ar.
      - empirical and molecular formulae
        
        Find the masses of the elements in the compound (by weight the compound then weighing it with elements taken out).
        
        Make these masses into percentages, divide each percentage by the ar of that element and you will have the number of atoms of it in a molecule.
        
        empirical formulae
        
        To find the empirical formula divide the molecular formula by the smallest number.
      - Calculating masses
        
        This means knowing that the mass of A and the mass of B will equal the mass of AB.
        
        Bearing in mind that the mass of one mole of an element is its atomic mass.
        
        If we have 2 moles of A(24) and react it with 5 moles of B(25)
        then we have (2x24)+(5x25) and can calculate that A2B5 will weigh 173g
      - calculating yield
        
        Theoretical yield
        
        Theoretical yield is what you expect to get, if a reaction doesn't finish you may end up with a lower yield than the expected theoretical yeild.
        
        To work out theoretical yield it is important to understand that an equation gives you a ratio of moles, e.g.
        Fe2O3 > 2Fe
        tells us that every one mole of iron oxide makes two moles of iron. In this equation the weight of Fe will be your yield.
        
        If we are told the weight of the Fe2O3 is 100g we can easily work out the theoretical yield:
        Work out the moles of Fe2O3 by doing the weight (g) divided by the atomic mass: 100/160= 0.625Mol
        
        We know that for every one mole of Fe2O3 there are two of Fe so we do: 0.625 x 2= 1.25 Mol
        Now we have moles of Fe we can work out weight by Mol x Ar: 1.25 x 56= 70g
- - - - Electrons are transferred from one atom to another (this is in an effort to either fill or empty the outer shell to become stable.)
      - n atom has no charge because the electrons and protons have equal and opposite charges.
      - But an ion will have a charge: an electron has a charge of -1, so loosing an electron looses one negative charge, making the ion +1.
      - The atoms the gain or loose electrons to each other will have opposite charges:
    - - The name given to loosing electrons is oxidation; the name given to gaining electrons is reduction.
      - OIL RIG
        
        Oxidation
        Is
        Loss
        Reduction
        Is
        Gain
    - - Dot and cross diagrams represent electron transfer. One atom will have dots as electrons, the other crosses.
    - - Ionic bonding happens between two ions
      - they are attracted to each other due to their opposite charges, so we say the ions have electrostatic attraction.
      - This attraction bonds them together into an ionic compound.
      - Breaking Ionic Bonds
        
        To melt or boil anything, heat is used to break bonds.
        
        The stronger the bonds, the more heat needed.
        
        Ionic compounds have strong bonds, so they don't melt or boil unless there is a considerable amount of heat, this means the have high melting and boiling points.
        
        The bigger the difference in charge, the stronger the attraction
        
        if you have + and - ions they will have a weaker bond than +3 and -3 ions.
        
        The stronger the attraction, the harder it is to break the bonds, this means that the melting and boiling points will be higher.
    - - An ionic crystal is a lattice of electrons in a 3D structure, the ions are alternate positive and negative and their opposing charges hold the structure together.
- - - - To draw a dot and cross diagram for a covalent bond, you need to draw the outer shells of the two atoms involved with an overlap, in this overlap should be the electrons they share.
      - Half the electrons in the overlap should be dots and half crosses, because one electron in every pair comes from each atom.
      - The rest of the electrons for the outer shell should be drawn on, one atom with dots, the other with crosses.
    - - A simple molecule (one with only a few atoms) will have a low melting point.
      - A substance with a simple molecular structure is one that contains only a few atoms in a molecule.
      - The intermolecular forces (between the molecules) are weak, so it doesn't take much energy- or heat- to break them- this means they will melt and boil under low heats, as even small amounts of heat energy are enough to break the bonds.
    - - A giant covalent structure is one with many atoms bonded together.
      - To melt or boil them you are not separating intermolecular bonds (between molecules), you are separating intramolecular bonds that keep the molecule together.
      - These bonds are strong covalent bonds which take a lot of energy to break, so a lot of heat energy is required before the bonds will break to boil or melt; meaning they have high melting and boiling points.
    - - Graphite
        
        Carbon atoms in Graphite are each bonded to three other atoms.
        
        In Graphite the atoms from layers, these layers can slide over each other, this makes it very slippery and so can be used as a lubricant.
      - Diamond
        
        Diamond is formed of carbon atoms each joined to four others.
        
        Diamond is extremely hard because it has a many bonds in it, this means it is great for cutting as it can cut anything.
- - - - Metals have delocalised electrons, electrons carry electricity; so because there are free electrons charge can pass easily through a metal.
    - - The structure of a metal is with rows of atoms on top of one another, in pure metals as all the atoms will be the same size, the layers can slide easily over one another making them easy to bend.
- - - - An electric current is a flow of electrons, although it can also be a flow of ions (as they have a charge.)
    - - In covalent compounds there are no electrons free to move, this means there can be no transfer of electricity through a covalent compound
    - - When ionic compounds are molten or in solution, the positive and negative ions separate this means that there are ions free to flow, and so they can conduct electricity.
    - - Experiment
        
        Set up an electric circuit with an LED and a break in the wire, put both ends of wire into a solution/molten substance.
        
        If the LED lights up then there is a current flowing, this will only be able to happen if the solution is conducting: so it must be an electrolyte.
        
        Conversely if the LED does not light up then there is no current flowing, and so the solution has not conducted electricity meaning it must be a nonelectrolyte.
    - - In electrolysis ionic compounds conduct electricity.
      - Positively charged ions move to one end, negatively to the other, these are then turned into atoms (by losing their charge) and so new substances are formed.
    - - Inert electrodes are ones that don't react with any other substances, but only play a role in the transfer of electrons.
      - Place inert electrodes (ones that wont react) into an aqueous solution.
      - At the positive electrode the negatively charged ion from the compound will form an atom. At the negative electrode the atom of the positive ion will form.
      - sodium chloride:
        
        Hydrogen at the negative
        
        chlorine at the positive
      - copper(II) sulfate:
        
        copper at the negative
        
        oxygen at the positive
      - dilute sulfuric acid:
        
        Hydrogen at the negative
        
        oxygen at the positive
      - If the metal in the solution is more reactive then hydrogen, the hydrogen from the water will be a product, as the metal will bond with the oxygen.
      - Test the products using known methods: eg damp blue litmus paper turned red by chlorine.