Chemistry C1

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  • Created on: 08-05-18 16:01
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  • Chemistry C1
    • States of matter.
      • Solids
        • Strong forces of attraction between particles, which hold them in fixed positions in a regular lattice arrangement.
          • Particles don't move- all solids stay in their definite shape and volume.
            • Vibrates in fixed position. the hotter a solid becomes, the more they vibrate.
              • If you heat a solid, it will eventually melt and become a liquid.
      • Liquids
        • Some forces of attraction between particles. They're free to move past each other but generally stay in their position.
          • Don't keep their definite shape and will flow and fill the bottom of a container. Keep the same volume.
            • Particles are constantly moving in a random motion. The hotter the liquid, the faster the particles move.
              • If you cool a liquid, it will freeze and become solid. If you heat a liquid enough, it will evaporate and become a gas.
      • Gases
        • No forces of attraction between the particles. They are free to move. They travel in straight line and  only interact when they collide.
          • Gases don't keep a definite shape or volume and will always fill any container. When particles bounce off the walls of a container, they exert a pressure on the walls.
            • The particles move constantly with a random motion, the hotter the gas gets the faster they move.
              • If you cool a gas, it will condense and become a liquid.
      • Particle theory: great model for explaining the three states of matter. However, particles aren't solid and they're not spheres- they're atoms, ions or molecules.
      • Doesn't give any ideas about the size of the particles or the space between them. Doesn't show the forces between them or how strong they are.
      • When a substance changes state, it's a physical change. No new substances are made the original chemicals just change state.
      • Physical changes are easy to undo by heating or cooling.
      • During a chemical reaction, bonds between the atoms break and the atoms change places. New products are made.
      • Compared to physical changes, chemical changes are often hard to reverse.
    • History of Atoms.
      • Atoms are the tiny particles of matter which make up everything in the universe.
      • At the start of  the 19th century, John Dalton said atoms were solid spheres and said that different spheres made up different elements.
      • In 1897, J.J Thompson 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. PLUM PUDDING MODEL
      • 1909 Ernest Rutherford and his students Geiger and Marsden conducted the famous gold foil experiment. They fired positively charged alpha particles at an extremely thin sheet of gold.
        • From the plum pudding model, they were expecting the particles to pass straight through the sheet or be spread out through the 'pudding; of the atom. Whilst most of the particles did go through the gold, some were deflected more than expected and a small number deflected backwards.
          • Rutherford came up with the theory of the nuclear atom to explain his new evidence. in this there is a tiny positively charged nucleus at the centre surrounded by negative electrons.
      • Niels Bohr proposed a new model where all the electrons where contained in shells.He suggested that electrons can only exist in fixed orbits and not anywhere in between. each shell has a fixed energy.
        • Bohr's theory of the atomic structure was supported by many experiments and it helped to explain lots of other scientists observations.
      • Our current model of the atom is different to what people thought the atom looked like in the past.
        • Scientists did more experiments, and new evidence was found and out theory of the structure of the atom was modified. These ideas can used to make predictions.
    • The Atom.
      • Made up of three subatomic particles. Protons, Electrons and Neutrons.
        • Protons are heavy and positively charged.
        • Electrons have hardly any mass and are negatively charged.
        • Neutrons are heavy and neutral.
      • Nucleus is the the middle of the atom. It contains protons and neutrons.It has a positive charge due to the protons. Almost the whole mass of an atom is in the nucleus.
        • Compared to the size of the atom, the nucleus is tiny.
      • Electrons move around the nucleus in electron shells.
        • They are negatively charged and very small but their orbitals cover a lot of space.
          • The volume of their orbitals determines the size of the atom. Electrons have virtually no mass.
      • Molecules are made up of two or more atoms. They can be made of the same or different elements.
        • The bonds that form between molecules are generally a similar length to the atomic radius.
          • Nano particles are a bit bigger than simple molecules (e.g. atoms). They're typically made up of around 100 atoms and range from 1nm to 100nm.
    • Atoms, Isotopes and Ions.
      • The atomic (proton) number tells you how many protons there are. Atoms of the same element all have the same number of protons.
        • To get the number of neutrons, just subtract the atomic number from the mass number.
      • The mass (nucleon) number is always the biggest number. On the periodic table the mass number is actually the relative atomic mass.
        • Neutral atoms have no charge overall. This is because they have the same number of protons and electrons. the charge on the electrons is the same size as the charge of the protons but opposite.
      • Ions form when atoms gain or lose electrons. .
        • Negative ions form when atoms gain electrons, they have more electrons than protons
          • Positive ions form when atoms lose electrons, they have more protons than electrons.
      • Isotopes are different forms of the same element, which have the same number of protons but different neutrons.
        • They have the same atomic number but different mass numbers.

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