${\rm{B}}{{\rm{r}}_2}$

${{\rm{F}}_2}$

${{\rm{I}}_2}$

${\rm{C}}{{\rm{l}}_2}$

Exothermic change

Endothermic change

Nuclear change

Photochemical change

$Ca{H_2}$

$Mg{H_2}$

$Ba{H_2}$

$Sr{H_2}$

$\alpha$ -particles

$\beta$-particles

$\gamma$-rays

Neutrons

1 electron, 1 proton, 1 neutron

1 electron, 2 protons, 1 neutron

1 electron, 1 proton, 2 neutrons

1 electron, 1 proton, 3 neutrons

They are ionic compounds

They are formed by transition metals

They are strong reducing agents

They react with water to liberate hydrogen gas

${{\rm{O}}_2}$

${{\rm{N}}_2}$

${\rm{C}}{{\rm{l}}_2}$

${{\rm{H}}_2}$

Deuterium

Helium

Tritium

Hydrogen

Strong nuclear force

Electromagnetic force

Gravitational force

Weak nuclear force

The reaction requires a large amount of heat to start.

A large amount of heat is absorbed during the reaction.

A large amount of heat is released during the reaction.

The reaction proceeds very slowly.

Scheele

Berzelius

Cavendish

Priestley