Page 15 - Curriculum Visions Dynamic Book

Notes on Key facts
The key facts, such as the example given below for cobalt, present a summary of the information on each element.They appear in a form that allows direct comparisons between elements.
Atomic number
The number of a chemical element based on the number of protons in the nucleus. The number of protons always equals the number of electrons in the atom.
For example, an atom of actinium has 89 protons in its nucleus, so its atomic number is 89.This number can also be obtained by adding the electrons in the shell diagram. In the case of actinium this is 2–8–18–32–18–9–2 = 89.
Atomic weight
The ratio of the average mass of a chemical element’s atoms to one-twelfth the mass of an atom of carbon-12.
Most chemical reactions take place between atoms. Because it is impossible to count the atoms directly, the reactants and products are weighed and calculations are based on atomic weights. Experimentally determining the atomic weights of the elements was one of the most important achievements of chemists.
Position in Periodic Table
The location of the element in the Periodic Table given on pages 6-7 of this book.
State at room temperature
Whether it is a solid, liquid or gas.
Colour
The commonly observed colour of the pure element before it has had a chance to react with its surroundings. Some elements react almost instantaneously with their
Key facts...
Name: cobalt
Symbol: Co
Atomic number: 27
Atomic weight: 58.93
Position in Periodic Table: transition metal,
group (9) (cobalt group); period 4 State at room temperature: solid Colour: lustrous, metallic grey Density of solid: 8.9 g/cc
Melting point: 1,495°C
Boiling point: 2,870°C
Origin of name: from the German word kobald,
meaning goblin
Shell pattern of electrons: 2–8–15–2
Name
The name generally accepted. Some of the most recently discovered elements may not have internationally agreed names. Detail about the variation in the names is provided in the section of the page headed Discovery. Names beginning with Un- are intentionally temporary names that will be changed once international agreement on them has been obtained.
Symbol
This is the chemical symbol for the element. For those for which the name has not been agreed, the chemical symbol can be expected to change when a final name is assigned to the element.
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