By number of protons/electrons.
Atoms of the same element may differ from one another by having differing numbers of Neutrons in their centres.
An element is a composition of many atoms. Thus you can hold NaCl (salt) in your hand. You can't hold the atoms it makes up.
An element is a composition of many atoms. Thus you can hold NaCl (salt) in your hand. You can't hold the atoms it makes up.
No. Atoms of the same element have the same chemical properties.
These atoms are known as valence atoms.
Yes
number of protons
isotopes
Neutrons. If the differ in electrons they are not neutral and if they differ in protons then they are no longer the same element as the number of protons determines the name of the element.
During chemical reactions atoms remain unchanged.
They are called isotopes.
They are called isotopes.