<\/o:p><\/span><\/span><\/p>\nCompounds are made up of fixed proportion of elements: They have a fixed proportion. Chemists call this the \u201cLaw of constant composition<\/b>\u201d. The forces that hold atoms together in compounds are called \u201cChemical bonds<\/b>\u201d. Reaction between elements and oxygen is called an oxidation reaction as the substance gains oxygen. Some examples<\/o:p><\/span><\/p>\n2Mg (S<\/sub>) + O2<\/sub>(g<\/sub>) \u2192 2MgO(S<\/sub><\/o:p><\/span><\/p>\nC(s)<\/span> + O2<\/sub>(g)\u2192 CO2<\/sub>(g<\/sub>)<\/o:p><\/span><\/p>\nWhen substances react such that there is a loss of oxygen, the process is called reduction. Some examples:<\/o:p><\/span><\/p>\nCuO (S<\/sub>) + H2<\/sub>(g)<\/sub> \u2192Cu(S<\/sub>) + H2<\/sub>0(g<\/sub>).<\/o:p><\/span><\/p>\nFe2<\/sub>O3(S<\/sub>) + 3CO(g<\/sub>) \u2192 2Fe(S<\/sub>) + 3CO2<\/sub>(g<\/sub>)<\/o:p><\/span><\/p>\nLook at these REDOX<\/b> reactions<\/o:p><\/span><\/p>\n1. <\/span>This is an example of oxidation reaction<\/o:p><\/span><\/p>\nCarbon + Oxygen \u2192 Carbon dioxide<\/o:p><\/span><\/p>\nC(s) + O2<\/sub>(g) \u2192 CO2(<\/sub>g)<\/o:p><\/span><\/p>\nOxidation reaction is gain of oxygen, loss of hydrogen or electrons.<\/o:p><\/span><\/p>\n2. <\/span>This is an example of a reduction reaction<\/o:p><\/span><\/p>\nCopper Oxide + Hydrogen \u2192 Copper + Water<\/o:p><\/span><\/p>\nCuG(s)<\/sub> + H2<\/sub>(g<\/sub>) \u2192 Cu (S<\/sub>) + H2<\/sub>O(g<\/sub>)<\/o:p><\/span><\/p>\ndeduction reaction is loss of oxygen, gain of hydrogen or electron.<\/o:p><\/span><\/p>\n<\/span> <\/span><\/span><\/span><\/b>MOLECULES<\/span><\/b><\/span><\/h2>\n<\/p>\nThe atoms are joined together in small groups. These small groups are called \u201cmolecules\u201d.<\/i><\/b> For example the atoms of Hydrogen, Iodine, Chlorine, Nitrogen, Oxygen, Fluorine and Bromine are each joined in pairs and are known as \u201cdiatomic\u201d<\/b>molecules, Phosphorus atoms are joined in four and sulphur in eight. In chemical shorthand the molecule of Chlorine is written s Cl2<\/sub>.<\/o:p><\/span><\/span><\/p>\nThe gaseous element helium, neon, argon, krypton, Xenon and Radon are composed of separate and individual atoms. They are \u201cmonatomic\u201d<\/b>; they are shorthanded Ne, Ar, Kr, Xe and Rn respectively.
![\"ELEMENTS,](\"https:\/\/i0.wp.com\/media.proprofs.com\/images\/QM\/user_images\/2503852\/New%20Project%20%2826%29%28120%29.jpg?resize=640%2C315&ssl=1\" "\\"ELEMENTS,")
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