Why is the atomic number used to identify atoms instead of atomic mass?

Answer 1

Atomic Number is the number of protons in the nucleus. It is also the number of electrons the atom has. It is the number of electrons that determines the chemical behavoir of the atom. Mass number is the number of Protons and Neutrons the nucleus has. Neutrons have no effect on the electron number and therefore on the atom's chemical behavoir. So atoms with the same Atomic Number and different Mass Number all have the same chemical properties. This then is a usefull way to define an "element". Atoms with different Atomic Numbers will have very different chemical properties, regardless if their Mass Numbers are equal or not so it would not be very usefull to call two atoms with different chemical properties the same element.

Answer 2

Different elements may have the same number of nucleons, but no two elements will have the same number of protons, hence the atomic number is most reliable when it comes to identifying an element.

Answer 3

Atomic number is the number of protons in the nucleus of an atom and is the same for all atoms of the same element. The elements are arranged in increasing order of atomic number on the periodic table. Atomic Mass is the mass of an atom and can vary within atoms of the same element. This is because the number of neutrons can vary for atoms of the same element. So, long story made short, atomic number does not vary for an element, but atomic mass can.

Answer 4

The atomic number of an element is the number of protons in an atom's nucleus, which is the same as the number of electrons when the atom is neutral. The number and configuration of an atom's electrons are what determines most of an element's chemical and physical properties. Variations in the atomic mass of an element are due to varying number of neutrons. Since neutrons are not electrically charged they have no influence on electrons and so have little effect on an element's properties.

Answer 5

The atomic number is used to identify atoms because it represents the number of protons in the nucleus of an atom, which determines the element's identity. Atomic mass, on the other hand, is the sum of protons and neutrons and can vary due to isotopes. Atomic number provides a more specific and consistent way to classify elements.

Answer 6

The Periodic Table pre-dates knowledge of the precise mass of atoms.