Lewis diagrams- grade 10 chemistry

can someone explain this to me?

Lewis diagram:
well first you have to know the Valence electrons the elements which will on top of the periodic table.

for examples:
H2O
it will be O-H-O and the dots will on top. oxygen have 6 valence electrons so that mean it need 6 dots. also for H it will have 7 V-electrons.

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium