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Exothermic reaction and endothermic reaction:
On the basis of energy changes during chemical reaction, they can be classified as
i) Exothermic reaction: A chemical reaction in which heat energy is produced.
Eg : C + O2 CO2 (g) + heat
ii) Endothermic reaction: A chemical reaction in which heat energy is absorbed.
Eg : CaCO3 + Heat CaO + CO2
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metals : - those elements have tendency to loose electrons and form cations is called metals.
ex: - sodium, potassium, etc.
scientific reasons : - the last shell of any metals contain one, two, or three electrons can easily loose to become stable.
group number = number of electrons in their valence shell.
metal in group 1 have only one electrons in their outermost shell so, are more reactive in nature than metals of other groups.
non - metals : - those elements have tendency to gain electrons and form anion is called non - metals.
ex : - chlorine, fluorine, oxygen, nitrogen.
their outermost shell contains 5,6,7 electrons.
for non metals : -
group number = 10 + valence electrons.
non - metals of group 17 are reactive metals are known as more electronegative elements because can snatch electrons from any metals and form anion to become stable.
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