Question

what happens when atoms of elements combine by sharing electrons or by the complete transfer of electrons from one atom to another?

Answer 1

They create a different substance because on the periodic table each substance has a certain amount of protons and if you add or take away protons and/or electrons it will create a different substance. For Example Nickel has 28 protons but if you add 2 more you get zinc and that has 30 protons. Another Example is
what if you have Titanium which has 22 protons and take away 2 you get Calcium which has 20 protons.

ps: The periodic table is attached as a picture to this answer
"AB84"