Prabin Kalikote

The elements or compounds that take part in a chemicalreaction are reactants and the elements or compoundsthat are formed as a result of a chemical reaction arecalled products.

for example

H₂SO₄ + Zn ----------> ZnSO₄ + H₂

ReactantsProducts

A chemical equation is an equation that representsthe chemical reaction with the symbols and molecularformulae of the reactants and products.

For example: 2H₂+ 0₂ --------> 2H₂O

A chemical reaction expressed by writing the fullnames of reactants and products is called a wordequation. For example:

Hydrogen + oxygen ----------->Water

The combination or displacement that occurs in themolecules of matter during a chemical changecalled a chemical reaction.Any two examples are:

1. 2H₂ + 0₂ -------> 2H₂0
   
2. H₂SO₄ + Zn ---------> ZnSO₄ + H₂

We know, lanthanides are rare earth metals, and actinidesare radioactive metals. The properties of lanthanidesresemble each othervery closely but are differentfrom the rest elements due to the preferential fillingof f-orbitals. So, they are placed separately to avoidunnecessarysidewise expansion of the periodic table.

When we move from top to bottom in a group of non-metal,the atomic size increases gradually. Hence, nuclearattraction for incoming electrons decreases. As a result,the tendency of non-metallic atoms to gain electronsdecreases. Therefore, chemical reactivity of non-metals decreaseson moving down in a group.

When we move from top to doon of periodic groups ofmetals, the atomic size increases gradually. Due to this,nuclear attraction to the valence electron decreases.As a result, the tendency of metal atoms to loseelectrons increases. Hence chemical reactivityof metalsincreases when moving from top to bottom in a group.