Topic 1

Topic 1

1. Atoms consist of electrons surrounding a nucleus that contains protons and neutrons.

2. Neutrons are neutral, but protons and electrons are electrically charged. Protons have a relative charge of +1, while electrons have a relative charge of -1.

3. he number of protons in an atom is called its atomic number. In the periodic table atoms are arranged in atomic number order.

4. Each atom consists of a nucleus containing protons and neutrons, with electrons arranged around it in energy levels

5. Chromatography: This is good for separating dissolved substances that have different colours, such as inks and plant dyes. It works because some of the coluored substances dissolve in the liquid better than others, so they travel further up the paper.

6. Filtration: Filtration is good for separating an insoluble solid from a liquid. (An insoluble substance is one that does not dissolve). Sand, for example, can be separated from a mixture of sand and water using filtration. That's because sand does not dissolve in water.

7. Evaporation: This is good for separating a soluble solid from a liquid (a soluble substance does dissolve, to form a solution). For example copper sulphate crystals can be separated from copper sulphate solution using evaporation. Remember that it is the water that evaporates away, not the solution.

8. Simple distillation: This is good for separating a liquid from a solution. For example, water can be separated from salty water by simple distillation. This method works because the water evaporates from the solution, but is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.

9. Fractional distillation: This is good for separating two or more liquids from each other. For example, ethanol (alcohol) can be separated from a mixture of ethanol and water by fractional distillation. This method works because the two liquids have different boiling points.

10. Plum pudding model of the atom: An early model - scientific idea - about the structure of the atom was called the plum pudding model. In this model, the atom was imagined to be a sphere of positive charge with negatively charged electrons dotted around inside it like plums in a pudding. Scientific models can be tested to see if they are wrong by doing experiments. An experiment carried out in 1905 showed that the plum pudding model could not be correct.

11. The nuclear model atoms have a small central nucleus surrounded by electrons The structure of the atom Atoms contain three sub-atomic particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in energy levels around the nucleus. The table shows the properties of these three sub-atomic particles.