definitions

Matter

Any substance that possesses mass and occupies physical space.

Element

A fundamental chemical substance consisting of atoms with the same number of protons, which cannot be broken down into simpler substances by ordinary chemical reactions.

Proton

A positively charged subatomic particle found within the atomic nucleus, possessing a relative charge of $+1$ and a relative mass of $1$.

Neutron

An uncharged subatomic particle residing in the atomic nucleus, possessing a relative charge of $0$ and a relative mass of $1$.

Electron

A negatively charged subatomic particle orbiting the atomic nucleus in specific energy levels, possessing a relative charge of $-1$ and a relative mass of approximately $\frac{1}{1836}$.

Atomic Number (Z)

The total number of protons found in the nucleus of an atom, defining the identity of a chemical element.

Mass Number (A)

The total number of protons and neutrons present in an atom's nucleus, calculated as $A = Z + N$, where $N$ represents the number of neutrons.