atomic structure 🧪

• nucleus is in the middle of the atom
• nucleus contains protons and neutrons
• nucleus has an overall positive charge
• almost the whole mass of the atom is concentrated in the nucleus
• electrons move around the nucleus in energy levels called shells
• electrons have a negative charge
• in a neutral atom, the number of protons is equal to the number of electrons so it has no charge overall
• atomic number: how many protons there are in an atom of that element
• mass number: total number of protons and neutrons in an atom of that element
• solids:

  • strong forces of attraction between particles
  • fixed position / regular lattice arrangement
  • definite shape and volume
  • particles vibrate (the hotter the solid becomes the more they vibrate)
• liquids:

  • some force of attraction between particles
  • free to move past one another but do stick together
  • no definite shape + sink to bottom of containers
  • particles constantly moving with random motion (the hotter the liquid gets the faster they move)
• gases:

  • no force of attraction between particles - free to move
  • travel in straight lines
  • only interact when they collide
  • no definite shape or volume
  • always fill any container
  • pressure exerted when they bounce off the walls of a container
  • move constantly with random motion (the hotter the gas gets the faster they move)
  • expand when their pressure increases
• all 3 states of matter expand when heated
• volatility:

  • when a liquid is heated the heat energy is transferred to the particles which makes them move faster
  • some particles move faster than others
  • fast moving particles at the surface will overcome the forces of attraction from the other particles and escape (that’s evaporation)
  • volatility is how easily a liquid evaporates
• elements consist of one type of atom only
• atoms in gases are often found in pairs
• nitrogen is the most common element in air (at around 78%)
• a compound is a substance made of two or more different elements that are chemically bonded
• it’s difficult to separate chemically bonded elements in compounds
• mixtures are elements that have not been chemically bonded and are easy to separate
• you can separate mixtures with physical methods like distillation
• mendeleev created the first periodic table in 1869
• in mendeleev’s table, elements with similar chemical properties were placed in the same vertical groups
• mendeleev discovered he had to leave gaps to make his table work
• with the gaps in mendeleev’s table, properties of undiscovered elements could be predicted
• neutron’s relative mass: 1
• isotopes: different forms of the same element which have the same number of protons but different numbers of neutrons
• radius of an atom is around 10000 times the radius of the nucleus
• compounds have totally different properties to the original elements
• chromatography: a way to identify different artificial colours / dyes
• chromatography:

  1. put spots of each coloured solution on a pencil baseline on filter paper (do not use pen - it might dissolve)
  2. put the paper in a beaker with some solvent but keep the baseline above the level of the solvent
  3. the solvent seeps up the paper, taking the dyes with it
  4. different dyes form spots in different places