Question

What is atomic number ?

Answer 1

Definition

• Atomic number is defined as the number of protons present in an atom of an element.
• It is denoted by the letter “Z”.
• Atomic number is always written as a subscript on the left-hand side of the chemical symbol.
• No two elements can have the same atomic number.
• When we are considering a neutral atom, the number of protons equals the number of electrons in it.
• So we can say that, the atomic number of an element is equal to the number of electrons present in the neutral atom of that element.

Example

• Name of the element having chemical symbol $\mathrm{Na}$ = $\mathrm{Sodium}$
• Atomic number of $\mathrm{Sodium}$ = $11$
• Number of protons = Atomic number = $11$
• Number of electrons of neutral atom = Number of protons = $11$