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Chemistry - Topic 2 - Bonding, Structure and Properties of Matter…

- - - - Each carbon atom forms four covalent bonds in a very rigid giant covalent structure.
    - - Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom also has one delocalised (free) electron.
    - - Sometimes called silica, this is what sand is made of. Each grain of sand is one giant structure of silicon and oxygen.
- - - - The displayed formula shows the covalent bonds as single lines between atoms.
      - This is a great way of showing how atoms are connected in large molecules. However, they don't show the 3-D structure of the molecule, or which atoms the the electrons in the covalent bond have come from.
    - - The 3-D model shows the atoms, the covalent bonds and their arrangement in space next to each other. But 3-D models can quickly get confusing for large molecules where there are lots of atom to include. They don't show where the electrons in the bonds come from either.
    - - You can use dot and cross diagrams to show the bonding in covalent compounds.
      - Electrons drawn in the overlap between the outer orbitals of two atoms are shared between those atoms.
      - Dot and cross diagrams are useful for showing which atoms the electrons in a covalent bond come from, but they don't show the relative sizes of the atoms, or how the atoms are arranged in space.
- - - - The tubes are very long in comparison to their diameter.
      - They are good electrical and thermal conductors along the tube due to their free electrons.
      - One kind of fullerene are nanotubes: Tiny carbon cylinders.
      - They have a high tensile strength. This means they don't break easily when stretched.
      - The use of small particles such as nanotubes is called nanotechnology. Nanotubes can be used in electronics or to strengthen materials without adding much mass and therefore weight.
- - - - The sodium atom gives up its outer electron, becoming an Na+ ion. The chlorine atom picks up the electron, becoming a Cl– (chloride) ion.
    - - The magnesium atom gives up its two outer electrons, becoming an Mg2+ ion. The oxygen atom picks up the electrons, becoming an O2– (oxide) ion.
    - - The magnesium atom gives up its two outer electrons, becoming an Mg2+ ion. The two chlorine atoms pick up one electron each, becoming two Cl– (chloride) ions.
    - - Two sodium atoms each give up their single outer electron, becoming two Na+ ions. The oxygen atom picks up the two electrons, becoming an O2– ion.
- - - - The particles don’t move from their positions, so all solids keep a definite shape and volume.
      - The particles vibrate about their positions - the hotter the solid becomes, the more they vibrate
      - Strong forces of attraction between particles, which holds
        them close together in fixed positions to form a very regular lattice arrangement.
    - - Liquids have a definite volume but don’t keep a definite shape,
        and will flow to fill the bottom of a container.
      - The particles are constantly moving with random motion. The hotter the liquid gets, the faster they move. This causes liquids to expand slightly when heated.
      - Weak force of attraction between the particles. They’re randomly
        arranged and free to move past each other, but they tend to stick closely together.
    - - the temperature
      - the pressure
      - the material
    - - Gases don’t keep a definite shape or volume and will always fill any container.
      - The particles move constantly with random motion. The hotter the gas gets, the faster they move. Gases either expand when heated, or their pressure increases.
      - In gases, the force of attraction between the particles is very weak — they’re free to move and are far apart. The particles in gases travel in straight lines.