The outermost electrons of an atom that can be gained or lost in a chemical reaction. Valence electrons are very important in determining how an element reacts chemically with other elements.

Very weak forces that exist between molecules. The smaller the molecules, the weaker the Van der Waals forces. These forces were named after Johannes van der Waals (1837-1923), a carpenter’s son from Dutch who was trained as a physics teacher and later returned to the university to study the physical properties of the gases. Van der Waals’ research showed the existence of very weak forces between molecules, an interaction too feeble to be classified as “bonds”. Johannes van der Waals was awarded the 1910 Nobel Prize for physics. The first isolation of Van Der Waals molecules took place in the 1980s.

An oscillatory motion —a movement first in one direction and then back in the opposite direction. According to the famous physicist R.P. Feynmann “everything that living things do can be understood in terms of the jigglings and wigglings of atoms…”

Visible light coming from the sun is made up of seven different colours, which correspond to different electromagnetic waves. These colours are: red, orange, yellow, green, blue, indigo and violet. A rainbow is an arch of light comprised of all the colours of the visible spectrum in their order. We can also see the different colours of the visible light by using a prism (light analysis).

Chemical compounds that are light and can be readily vaporised but not easily dissolved in water. Many of them are human-made chemicals that are used and produced in the manufacture of paints, pharmaceuticals and refrigerants inducing short or long-term adverse health effects

Εlectrical potential energy per unit charge.