##### Matter_

1. Matter is anything that occupies space and has mass.

2. Matter can be classified into elements and compounds.

3. An element is a substance that consists of only one type of atom.

4. A compound is a substance that contains two or more elements that are chemically bonded together.

5. Matter is made up of tiny and discrete particles. There are spaces between these particles.

6. The particles may be atoms, molecules or ions.

7. An atom is the smallest particle of an element that can participate in a chemical reaction.

8. Metals and some non-metals such as carbon and noble gases exist as atoms.

9. A molecule is a neutral particle that consists of two or more atoms which are chemically bonded together.

10. An ion is a positively-charged or negatively-charged particle.

11. Particles in matter are in motion. This has been confirmed by many experiments such as the diffusion of bromine.

12. Diffusion occurs when the particles of a substance move between the particles of another substance from a region of high concentration to a region of a low concentration.

13. The rate of diffusion of gas particles depends on their masses.

(a) Gases with low molecular masses diffuse faster than those with high molecular masses.

(b) Figure 2.5 shows the set-up of the apparatus used to compare the rates of diffusion of ammonia gas, $$NH_{3}$$and hydrogen chloride gas, HCI.

(c) A white solid ring forms nearer to the hydrogen chloride end. The white solid is ammonium chloride $$NH_{4}CI$$, a compound produced from the reaction of ammonia gas and hydrogen chloride gas when they meet inside the glass tube.

(d) This experiment shows that the ammonia molecules move faster than the hydrogen chloride molecules.

(e) Ammonia gas diffuses faster than hydrogen chloride gas because the molecular mass of ammonia is less than that of hydrogen chloride.

14. The rate of diffusion is affected by the temperature.

(a) The higher the temperature, the faster the particles move and so the faster the diffusion.

(b) For example, the purple colour of potassium manganate(VII) spreads through the water much more quickly in hot water than in cold water.