Chemistry Paper 1

• Atom


  The smallest part of an element that can exist
• Types of substances


  • Wood
  • Metal
  • Plastic
  • Glass
• There are about 100 different types of atom found naturally on Earth
• Element


  A substance made up of only one type of atom
• Chemical symbol


  A symbol that represents an atom of an element
• The elements in the periodic table are arranged in columns, called groups, with each group containing elements with similar chemical properties
• Metals


  Elements to the left of the 'staircase' line in the periodic table
• Non-metals


  Elements to the right of the 'staircase' line in the periodic table
• Metalloids or semi-metals


  Elements lying next to the dividing line between metals and non-metals, with some metallic and some non-metallic properties
• Compound


  A substance made up of different types of atom bonded together
• The chemical formula of a compound shows the ratio of atoms of each element present
• Chemical bond


  A force that holds atoms tightly together in a compound
• Atoms are made up of a tiny central nucleus with electrons orbiting around it
• Chemical equation


  A representation of a chemical reaction showing the reactants and products
• In a chemical reaction, the atoms get rearranged but the total mass of the products is equal to the total mass of the reactants (Law of conservation of mass)
• Adding state symbols (s, l, g, aq) to a balanced chemical equation provides extra information about the physical states of the substances
• Mixture


  A combination of two or more substances that are not chemically combined
• Mixture


  • No fixed composition, proportions vary
  • Substances can be separated by physical means
• Compound


  • Fixed composition, ratio of elements is always the same
  • Substances are chemically combined
• Separation techniques for mixtures

  1. Filtration

  2. Crystallisation

  3. Distillation

  4. Chromatography
• Filtration


  Separating insoluble substances from soluble substances in a mixture
• Crystallisation


  Separating a soluble solid from a solvent by evaporating the solvent
• Distillation


  Separating a solvent from a mixture by evaporating and condensing the solvent
• Fractional distillation


  Separating miscible liquids with different boiling points using a fractionating column
• Paper chromatography


  Separating and identifying substances in a mixture based on their relative solubility in a solvent
• John Dalton proposed that substances are made up of atoms that are the fundamental building blocks of nature
• J.J. Thomson discovered the electron, a tiny negatively charged particle within atoms
• It was not until the early 1800s that the ideas about particles and atoms became linked to strong experimental evidence
• John Dalton put forward his ideas about atoms from his experiments, he suggested that substances were made up of atoms that were like tiny, hard spheres
• Dalton also suggested that each chemical element had its own atoms that differed from others in their mass
• Dalton believed that these atoms could not be divided or split, and they were the fundamental building blocks of nature
• In chemical reactions


  Atoms re-arrange themselves and combine with other atoms in new ways
• Dalton's ideas are still useful today for example, they help to visualise elements, compounds and molecules, as well as the models still used to describe the different arrangement and movement of particles in solids, liquids, and gases
• At the end of the 1800s, a scientist called J.J. Thomson discovered the electron, a tiny, negatively charged particle that was found to have a mass about 2000 times smaller than the lightest atom
• Thomson's experimental evidence for the existence of electrons

  1. Applying high voltages to gases at low pressure

  2. Observing the beams of particles that were attracted to a positive charge, showing they were negatively charged particles

  3. Calling the tiny, negatively charged particles electrons
• Thomson's experiments showed that Dalton's idea that atoms could not be divided had to be revised
• Thomson's model for the atom

  Negatively charged electrons embedded in a positive charge
• Geiger and Marsden's students were doing an experiment with radioactive particles, firing dense, positively charged particles (called alpha particles) at the thinnest piece of gold foil they could make
• Their results shocked them as the particles were repelled back towards their source, suggesting a new model for the atom
• Rutherford's atomic model


  The positive charge must be concentrated at a tiny spot in the centre of the atom (the nucleus), with electrons orbiting around this nucleus