Page 8 - Curriculum Visions Dynamic Book

of inert gases, it is often designated group 0 (since that is the number of electrons in the shell outside the stable shell of helium, which is
two, or of neon, argon, krypton, xenon and radon, which is eight). Sodium and potassium have only one electron in their outer shell (outside the stable inner shell of eight electrons) and so are in group 1.
Transition elements
When atoms have reached a certain complexity (atomic number 21), ten
more electrons can be accommodated in an inner shell.They correspond to the elements scandium to zinc and are called the transition elements.All of the transition elements are metals.They include most of the metals that have the greatest use.They include iron, copper, gold, nickel and silver. These elements have high melting points and high densities. Most can be alloyed (mixed) together to give materials with new and useful properties.
At lanthanum a further 14 electrons can be included inside the atomic structure, giving rise to the lanthanide series of inner transition metals. (The actual electron configuration is shown in the shell diagram for each element found on its page.)
Alternative grouping system
A recent method of numbering the groups of the Periodic Table that scientists have devised to refer to the transition metals more specifically in the Periodic Table uses the numbers 1 to 18 (shown in parentheses in the table on pages 6–7). In the key facts given for each element these numbers are also shown in parentheses – for example, for chromium: position in Periodic Table:
 Dmitri Ivanovich Mendeleev (1834–1907) was born in Siberia but moved to St Petersburg to
get his university degrees. He was professor of chemistry there from 1867.
transition metal, group (6) (chromium group); period 4. In the text only the older
group numbers shown on the Periodic Table are used.
Radioactive elements are different from all other elements
because they lose particles from the nucleus of their atoms (which is called decaying). As a result, over time a radioactive element will change its atomic number and turn into a different element. So, for example, uranium decays to lead.This is shown in equations by numbers before the chemical symbol (example 293 Uuo).
Metals,metalloids and non-metals
The Periodic Table (pages 6-7) shows
a distinct clustering between elements
that are metals (coloured orange) – and that have a metallic lustre and are good electrical and thermal conductors – and the non-metals (coloured purple) – which do not have a luster and are electrical and thermal insulators. Metals form oxides that are basic and so react with acids to produce salts. Non-metals form oxides that react with water to form acids.
Between these major clusters lie elements known as the metalloids, semi- metals, or semi-conductors.They are coloured yellow. Metalloids are unusual in that they are better conductors at high temperatures (the reverse of metals) and conduct electricity much less than metals but more than non-metals.
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