Key words
Element, atomic symbol, compound, metals, non-metals, properties, chemical reaction
What you need to know
Elements are listed in periodic table in order of increasing atomic number.
Atoms are also in groups: Group 1 to group 8. Group 1 have one electron in their outermost shell, group 2, 2 electrons in the outermost shell, group 3, 3 electrons in the outermost shell, ………. and group 8 have 8 electrons in their outermost shell.
Atoms of an element are represented by atomic symbols. These symbols can be made up of one letter, 2 or 3 letters.The first letter is always a capital letter / uppercase with subsequent letters, small letters / lower case.
How elements react
1. Metal + metal
No (chemical) reaction
Note: two or more metals can form alloys (mixture).
2. Metal + non-metal
Formation of ionic compound; positive and negative ions formed.
Involves transfer of electrons from the metal to the non-metal.
Metals loss electrons to form positive ions
Non-metals gain electrons to form negative ions.
Example, sodium react with oxygen to form sodium oxide.
3. Non-metal + non-metal
Formation of molecular compounds (molecules are formed).
Involves sharing of electrons.
Example, carbon and oxygen share electrons during a chemical reaction to form carbon dioxide.
Retrieval Practice
Classify the following as ionic, molecular or metals
1. Oxygen
2. Sulfur dioxide
3. Potassium iodide
4. Sodium chloride
5. Brass
6. Hydrogen chloride
GCSE SCIENCE 