5.1.2 The Nucleus

Objective: Know the relationship between the proton number and the relative charge on a nucleus.

The nucleus is the central part of an atom. It contains protons and neutrons. The number of protons in the nucleus is a defining characteristic of an element and determines its atomic number.

Proton Number and Atomic Number

The proton number of an element is the number of protons in the nucleus of a single atom of that element. This number is also known as the atomic number, denoted by the symbol Z.

Charge of a Proton

Protons have a positive electrical charge. The magnitude of this charge is defined as +1 elementary charge. The elementary charge, denoted by e, is approximately $1.602 \times 10^{-19}$ Coulombs.

Relationship between Proton Number and Relative Charge

The relative charge of a nucleus is determined by the number of protons it contains. Since each proton carries a +1 charge, the relative charge of the nucleus is equal to the number of protons.

Therefore, the relative charge of a nucleus is given by:

$$ \text{Relative Charge} = \text{Number of Protons} = Z $$

Table Summarizing the Relationship

Concept	Description
Proton Number (Z)	The number of protons in the nucleus of an atom.
Atomic Number (Z)	Another name for the proton number.
Charge of a Proton	A positive electrical charge of +1 elementary charge ($1.602 \times 10^{-19} \text{ C}$).
Relative Charge of the Nucleus	The positive electrical charge of the nucleus, equal to the number of protons.

Example

Consider an atom with 6 protons in its nucleus. This atom has an atomic number of 6 and a relative charge of +6.

$$ \text{Number of Protons} = 6 $$

$$ \text{Relative Charge} = +6 $$