What is the relation between atomic number and atomic mass?

 

Atomic Number

Atomic Number is the number of protons in an atom. Protons are known to exist in an atom's nucleus. The atomic number of an atom is determined by the number of protons in the atom. As a result, we may define an atomic number as:

The atomic number of an element is the number of protons in one atom. An element's atomic number equals the number of protons in one atom of the element is termed as Atomic Number.

The atomic number of sodium, for example, is 11, since one atom of this element has 11 protons. A carbon atom, for example, has six protons, giving it an atomic number of sixes, whereas a hydrogen atom has just one proton in its nucleus. As a result, hydrogen has an atomic number of ones. The letter Z represents an element's atomic number.

• All atoms of the same element have the same number of protons and hence the same atomic number.
• The amount of protons in the nuclei of various elements varies.
• The atomic number of two elements cannot be the same.
• Because each element has a unique atomic number, the atomic number may be used to identify it.

For example, if the atomic number is 6, it indicates that the element is carbon. There is no other element with an atomic number of 6. Thus, the atomic number differentiates one element's atoms from the atoms of another element. Because different elements have distinct atomic numbers, their atoms differ. The number of protons in a typical atom is equal to the number of electrons. As a result, we may state-

Atomic number of an element = Number of electrons in one neutral atom

Only a neutral atom has an equal number of protons and electrons; an element's atomic number is equal to the number of electrons in the neutral atom, not the ion. An ion, on the other hand, is formed by either removing or adding electrons to a conventional atom, and therefore contains either fewer or more electrons than protons. Chemical processes solely involve the electrons of atoms, not their protons. The number of electrons can change throughout a chemical reaction, while the amount of protons does not. As a result, the atomic number of an element does not change throughout a chemical reaction and stays constant.

Mass Number

Protons, neutrons, and electrons make up an atom. Because electrons have a tiny mass in comparison to protons and neutrons, the mass of an atom is determined solely by protons and neutrons. The mass number of an element is the total number of protons and neutrons contained in one atom.

The mass number is equal to the sum of the number of protons and neutrons or, 

Mass number = Number of protons + Number of neutrons

One atom of sodium, for example, contains 12 neutrons and 11 protons, therefore the mass number of sodium is 11+12=23. Similarly, because a carbon atom contains 6 protons and 6 neutrons, its mass number is 6+6=12.

A hydrogen atom has one proton but no neutrons. As a result, the mass number of hydrogen is only one. The letter A represents an element's mass number. Because the mass of the sodium atom is 23, we may state that A=23 for sodium.

Notation of the Atomic Number and Mass Number 

If the element is X, then the atomic number Z and mass number A are written in chemical notation as-

Symbolic representation of an atom	Atomic number	Mass number
AXZ           X ⇒ Element           A ⇒ Mass no. of an element           Z ⇒ Atomic no. of an element	Z = e = p Z ⇒ Atomic no. e ⇒ No. of electrons p ⇒ No. of protons	A = p + n A ⇒ Mass no. of an atom n ⇒ no. of neutrons p ⇒ No. of protons.