Why is an atom of one element different from the atoms of other elements?

The combining capacity of atoms of an element with the atoms of other element is called its valency. Based on valency the odd one is

What is atomic mass of an element?

Do the atoms of each element on left side equal to the atoms of the element on the right side of the equation?

Can carbon form bonds with the atoms of other elements?

The atoms of elements are with

Why are the atoms of different elements different?

Tracheids differ from other tracheary elements in

The mass of 1.5xx10^(20) atoms of an element is 15mg. The atomic mass of the element is

There are more number of atoms in one gram atom of an element than in one gram of the same element. Explain.