STD VIII – ATOMIC STRUCTURE (Hybrid)

Atoms are made up of three particles: protons, neutrons, and electrons.

Nucleus: It is the centre of the atom. It contains protons and neutrons.

Protons are always positively charged. The number of protons in the atom is called its atomic number(also called proton number). In the Periodic Table, atoms are arranged in atomic number order. Protons have a relative charge of +1.

Neutrons have a neutral charge.

Electron cloud: It is the outer portion of the atom.

Electrons: They are negatively charged and are arranged around the nucleus in shells or orbits. They have a relative charge of –1

The total number of electrons in an atom is always the same as the number of protons in the nucleus.

The nucleus of the atom

The number of protons and electrons are equal in atom which is therefore electrically neutral

Protons and neutrons are called nucleons since they occur inside the nucleus

Atomic number (Z) = Number of protons in the nucleus. In a neutral atom, number of protons=number of electrons (not in ions)

Mass number (A) = number of protons+ number of neutrons