Page 16 - Curriculum Visions Dynamic Book

surroundings.Thus the colour given here and the colour most commonly observed (due to oxidation, and so on) may differ.
Density
A comparison of the densities of the gases can be made using a simple calculation based on the idea that 24 litres of any gas at room temperature and standard pressure will have a mass in grams equal to its molecular weight. Most gaseous elements exist as diatomic molecules, for example, O2, N2 and so on.
Examples:
Oxygen (atomic weight 16) Molecular weight of O2 = 2 x 16 = 32 Thus density = 32/24 = 1.3g/l
Hydrogen (atomic weight 1) Molecular weight of H2 = 2 x 1 = 2 Thus density = 2/14 = 0.083g/l
The noble gases exist as single atoms. Helium (atomic weight 4) Molecular weight of He = 4
Thus density = 4/24 = 0.17g/l
Melting point/boiling point
Because of the difficulty in obtaining absolutely pure samples of some elements, the unstable nature of some elements and the difficulties
in taking the measurements at high temperatures, variations can be found between sets of published data.The values given in the key facts of these books are typical quoted values from established scientific institutions.
Origin of name
The derivation of the name is given.
The main text may explain this derivation more fully.
Shell pattern of electrons
Electrons move in certain places around the nucleus.These places are known as shells.The shell pattern is thus the pattern of electrons that surrounds the nucleus of an atom.The list is given from the centre outward.The shell pattern corresponds to the shell diagram given on each page.
Shell diagrams
The shell diagrams, such as the ones shown below, are colour-coded to match the Periodic Table on pages 6-7. Hydrogen and other non-metals are coloured purple. Metals are orange, with the actinide and lanthanide series green. Metalloids (semi- metals) are coded yellow.
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