Atoms & Elements

Atoms & Elements

1. The atom is made up of Electrons, Protons and Neutrons. The overall charge is neutral, this is because the number of protons and electrons is equal.(They cancel out)

   • Electron- Negatively charged, relative mass is very small. Neutron- No charge, relative mass is 1. Proton- Positively charged, relative mass of 1.
   • A compound is when atoms of different elements are chemically bonded together
   • A mixture is made up of two or more substances that have not been chemically combined. They can be separated and their chemical properties do not change.

2. Key Features of a chemical reaction- Compounds formed/broken, At least 1 new substance, No atom created/destroyed, Measurable energy change. \when written the equation is balanced as no atom is created/destroyed.

3. Separation Techniques

   • Crystallisation- Separates solutions into solids and liquids
     • Heat mixture, evaporate the solvent and collect it through condensing. The solute is left as crystals
   • Chromatography- Chromatography Separates solutions with a number of different solutes (solids) in the solvent (liquid).
     • Place a drop of the solution to be separated near the bottom of a piece of chromatography paper. Dip the very bottom of the paper into a suitable solvent. The solvent (liquid) moves up the paper and carries the solutes (solids) in the solution with it. Different solutes (solids) move at different speeds, so they separate on the paper.
   • Distillation- Separates 2 liquids with different boiling points
     • The mixture is heated until the liquid with the lower boiling point starts to boil. The vapour released passes through a condenser, where the gas cools back into a liquid. Simple distillation can also separate a solute from a solvent, when the solvent has a lower boiling point than the solute.
   • Fractional Distillation- Separates lots of liquids with different boiling points
     • The mixture is slowly heated until the liquid with the lowest boiling point boils and then condenses. Then we increase temperature slowly to collect (boil then condense) the other fractions.

4. The model of the Atom-

   • Thomson's Plum pudding model. this showed the atom as a ball of positive charges with negative electrons mixed in
   • The Nuclear model was next, it showed that an atoms mass can be concentrated in a central "nucleus" this contained positive protons
   • After that, Bohr discovered that electrons orbit the nucleus at fixed distances. Chadwick discovered that some particles in the nucleus have no charge at all, neutrons.

5. Atom Size- 0.1nm. Mass number= top number(P+N). Atomic number(P)= bottom