Page 22 - Curriculum Visions Dynamic Book

Colours
Metal oxides are useful colouring agents and they have been used since ancient times as the pigment (coloured material) in paint.
An oxide of a particular metal may also have various colours, depending on how much oxygen is combined with the metal. For example, iron oxides can be red (when combined with much oxygen) or black (when combined with a smaller amount
of oxygen).
The same rule applies to other metals, as you can see by the lead shown on this page.
 Lead oxides make a variety of colours. Massicot, a form of lead monoxide (PbO), is a yellow, crystalline compound. It is one of the most widely used and commercially important metallic compounds. The bright red powder is known as “red lead” (Pb3O4), whilst the darkest powder is lead dioxide (PbO2).
 The series of photographs across the bottom of these two pages shows the changing oxidation states of vanadium.
Oxidation does not necessarily involve adding oxygen. It can also be defined as
“loss of electrons”. Elements are said to have “oxidation states”, described by
a number indicating the number of electrons lost. Each oxygen atom attached to
an element corresponds to 2 lost electrons. Vanadium is a good example of a metal element that can be changed to several oxidation states, which have different colours as in the sequence of pictures shown below. Vanadium with the lowest oxidation state (2) is violet; with an oxidation state of 3 it is green; blue corresponds to an oxidation state of 4 and yellow to 5. The other colours are intermediate situations where two oxidation states are present (e.g. yellow plus blue appears green).
Also:
Vanadium colours
Vanadium, oxidation state 5
Transition Vanadium, oxidation state 4
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