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Chemistry Revision, C1 Practicals - Coggle Diagram

- - - - negatively charged and tiny, but cover a lot of space
      - the volume of their orbits determines the size of the atom
      - move around the nucleus in electron shells
      - negligible mass
    - - atoms are neutral
      - because they have the same number of protons and electrons
      - the size of the charge on electrons is the same as on the protons, but opposite, so they cancel out
      - in an ion, the number of protons doesn't equal the number of electrons. This means it has an overall charge
    - - positively charged because of the protons
      - almost all the mass is concentrated in the nucleus
      - has a radius of around 1 x 10^ -14
      - it's in the middle of the atom
      - it contains protons and neutrons
    - - the nuclear symbol of an atom tells you its atomic (proton) number and mass number
      - the atomic number tells you how many protons there are
      - the mass number tells you the total number of protons and neutrons in the atom
      - to get the number of neutrons, just subtract the number atomic number from the mass number
  - - - Rutherford came up with an idea to explain this new evidence - the nuclear model of the atom. In this, there's a tiny, positively charged nucleus at the centre, where most of the mass is concentrated. A 'cloud' of negative electrons surrounds this nucleus - so most of the atom is empty space. When alpha particles came near the concentrated, positive charge of the nucleus, they were deflected. If they were fired directly at the nucleus, they were deflected backwards. Otherwise, they passed through the empty space
      - scientists realised that electrons in a 'cloud' around the nucleus of an atom, as Rutherford described, would be attracted to the nucleus, causing the atom to collapse
      - from the plum pudding model, they were expecting the particles to pass straight through the sheet or be slightly deflected at most. This was because the positive charge of each atom was thought to be very spread out through the 'pudding' of the atom. But, while most of the particles did go straight through the the gold sheet, some were deflected more than expected, and a small number were deflected backwards. This meant the plum pudding model couldn't be right
      - Niels Bohr's nuclear model of the atom suggested that all the electrons were contained in shells
      - in 1909 Rutherford and his student Marsden conducted the famous alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold
      - Bohr proposed that electrons orbit the nucleus in fixed shells and aren't anywhere in between. Each shell is a fixed distance from the nucleus
      - the plum pudding model showed the atom as a ball of positive charge with negative electrons embedded in it
      - Bohr's theory of atomic structure was supported by many experiments and it helped to explain lots of other scientists' observations at the time
      - the 'solid sphere' idea of atomic structure had to be changed. The new theory was known as the 'plum pudding model'
      - further experimentation by Rutherford and others gave the conclusion that the nucleus could be divided into smaller particles, each of which has the same charge as a hydrogen nucleus
      - in 1897 JJ Thomson concluded from his experiments that atoms weren't solid spheres. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles - electrons
      - about 20 years after scientists had accepted that atoms have nuclei, James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus. These became known as neutrons. The discovery of neutrons resulted in a model of the atom which was pretty close to the modern day accepted version, known as the nuclear model
      - at the start of the 19th century John Dalton described atoms as solid spheres, and said that different spheres made up the different elements
      - electronic structure and the periodic table
        
        electron structure: 2,8,8,8...
        
        periodic table development
        
        early periodic tables were not complete and some elements were placed in the wrong group. This is because elements were placed in order of atomic weight and did not take into account their properties
        
        in 1869, Dmitri Mendeleev overcame some of the problems of early periodic tables by taking 50 known elements and arranging them into his table of elements - with various gaps
        
        back then, the only thing they could measure was atomic weight, and so the known elements were arranged in order of atomic weight. When this was done, a periodic pattern was noticed in the properties of the elements, which is where the name periodic table comes from
        
        Mendeleev put the elements mainly in order of atomic weight but did switch that order if the properties meant it should be changed.
        
        back then, scientists had no idea of atomic structure or of protons, neutrons or electrons, so there was no such thing as atomic number to them
        
        gaps were left to make sure that elements with similar properties stayed in the same groups. Some of these gaps indicated the existence of undiscovered elements and allowed Mendeleev to predict what their properties might be. When they were found, and they fitted the pattern, it helped confirm Mendeleev's ideas.
        
        until quite recently there were two ways to categorise elements
        
        their atomic weight
        
        their physical and chemical properties
        
        modern periodic table
        
        the group number tells you how many electrons there are in the outer shell, e.g. group 1 elements have 1 electron in their outer shell. The exception is helium, in group 0, with 2 electrons in its outer shell. This means elements in the same group all are likely to act in a similar way
        
        the rows are called periods. Each new period represents another full outer shell
        
        elements with similar properties form columns. These columns are called groups
        
        metals are found to the left, and non-metals to the right
        
        in the periodic table, there are 100ish elements, laid out in order of increasing atomic (proton) number. This means there are repeating patterns in the properties of the elements
        
        groups
        
        group 1
        
        the alkali metals are lithium, sodium, potassium, rubidium, caesium and francium
        
        they are all soft and have low density. The first three in the group are less dense than water
        
        they all have one electron in their outer shell. This makes them very reactive and gives them similar properties
        
        as you go down, the elements get more reactive - outer electron is more easily lost as the attraction between the nucleus and electron decreases, because the electrons get further away from the nucleus. They have lower melting and boiling points further down, and higher relative atomic mass
        
        the group 1 elements don't need much energy to lose their one outer electron to form a full outer shell, so they readily form 1+ ions
        
        it's so easy for them to lose their outer electron that they only ever react to form ionic compounds. These compounds are usually white solids that dissolve in water to form colourless solutions
        
        reaction with water - they react vigorously to produce hydrogen gas and metal hydroxides - compounds that dissolve in water to produce alkaline solutions. The amount of energy given out by the reaction increases as you go down the group
        
        reaction with chlorine - they react vigorously when heated in chlorine gas to form white metal chloride salts
        
        reaction with oxygen - react with oxygen to form a metal oxide
        
        group 7
        
        fluorine is a very reactive, poisonous yellow gas
        
        chlorine is a fairly reactive, poisonous dense green gas
        
        bromine is a dense, poisonous, red-brown volatile liquid
        
        iodine is a dark grey crystalline solid or purple vapour
        
        they all exist as molecules which are pairs of atoms
        
        as you go down, the halogens become less reactive - it's harder to gain an extra electron because the outer shell is further from the nucleus. They have higher melting and boiling points and higher relative atomic masses
        
        halogen atoms can share electrons via covalent bonding with other non-metals so as to achieve full outer shells. The compounds that form when halogens react with non-metals all have simple molecular structures
        
        the halogens form 1- ions called halides when they bond with metals
        
        metals/non-metals
        
        non-metals don't generally form positive ions when they react
        
        atoms generally react to form a full outer shell. They do this via losing, gaining or sharing electrons
        
        non-metals are in the far right and top of the periodic table
        
        metals to the left of the periodic table don't have many electrons to remove and metals towards the bottom of the periodic table have outer electrons which are a long way away from the nucleus so feel a weaker attraction. Both these effects mean that not much energy is needed to remove the electrons so it's feasible for the elements to react to form positive ions with a full outer shell
        
        most elements in the periodic table are metals
        
        for non-metals, forming positive ions is much more difficult. This is because they are either to the right of the periodic table - where they have lots of electrons to remove to get a full outer shell, or towards the top - where the outer electrons are close to the nucleus so feel a strong attraction. It's far more feasible for them to share or gain electrons to get a full outer shell
        
        they're towards the bottom of the periodic table, and to the left
        
        all metals have metallic bonding which causes them to have similar basic physical properties
        
        great heat and electrical conductors
        
        high boiling and melting points
        
        strong, but malleable
        
        metals are elements which can form positive ions when they react
        
        as non-metals don't have metallic bonding, they don't exhibit the same properties as metals. They tend to be more dull looking, more brittle, aren't always solid at room temperature, don't generally conduct electricity and often have a lower density
- - - - slowly heat the solution. the solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form
      - keep heating the evaporating dish until all you have left is dry crystals
      - pour the solution into an evaporating dish
    - - once some of the solvent has evaporated, or when you see crystals start to form, remove the dish from the heat and leave the solution to cool
      - the salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
      - pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate and the solution will get more concentrated
      - filter the crystals out of the solution, and leave them in a warm place to dry. You could also use a drying oven or desiccator