Nucleons

Of what parts is an atom formed?

An atom is constituted by:

a central nucleus
electrons (negatively charged) that turn around it.

Animated drawing of an atom with electrons orbiting the nucleus — Electrons move around the nucleus

Schematic representation of an atom: protons and neutrons in the nucleus and electrons in the periphery — Schematic representation of the parts of an atom

The atomic core is made up of nucleons that are of two fundamental classes:

protons (positively charged)
neutrons (without any charge)

The number of protons and neutrons of the nucleus defines the various isotopes of an element.

The electrons reside in atomic orbitals that have defined shapes

Atomic orbitals of sodium: 1s, 2s, the three 2p and 3s, superimposed around the nucleus — Atomic orbitals of the element sodium

Atomic orbitals are distributed in shells (1, 2, 3, etc.) and are designated letters (s, p, d, f). Each of them has a specific way in which electrons reside.
S orbitals are spherical. The others have a shape similar to that of two balloons joined at the inflation mouth.

The size of the atoms is really tiny. That of its particles is even smaller so, believe it or not, an atom is a essentially empty entity.

A hydrogen atom consists of only one proton and one electron. It can be considered as a sphere with a radius of 0.0000001 mm. Its nucleus in turn is another sphere of radius 0.000000000001 mm, that is, 100,000 times smaller. Electrons are even smaller, so tiny that their size has not yet been accurately measured. Indirect evidence indicates that its size cannot be greater than 0.000000000000001 mm, that is, 1,000 times smaller than the nucleus.

With these measurements it is easy to calculate that 99.99999999999999% of the volume of an atom is just emptiness.

The particles that form the nucleus: nucleons

With the word nucleon we refer to both protons (p) and neutrons (n). They practically have the same mass. The proton has a positive electrical charge. The neutron is electrically neutral.

Schematic representation
of a 7-lithium nucleus

Lithium-7 nucleus, with three protons and four neutrons, each 1.6 fm across

The nucleons have a size of 0.0000000000016 mm or 1.6 femtometers (fm). The core of atoms with several nucleons is not much larger because these are tightly packed by extraordinarily strong forces.

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