Valency is the combining capacity of an atom, determined by the number of electrons it can gain, lose, or share to achieve a stable electron configuration. Different types of valencies include the positive valency (number of electrons lost), negative valency (number of electrons gained), and covalency (number of electrons shared in a covalent bond).

An activity to understand the implications of Rutherford's α scattering experiment with a gold foil involves directing a beam of alpha particles at a thin gold foil and observing the scattering pattern on a fluorescent screen. This demonstrates that most alpha particles pass through the foil undeflected, while a small fraction are scattered at large angles, indicating the presence of a concentrated positive charge (nucleus) in the atom.

Rutherford's α-particle scattering experiment involved directing a beam of alpha particles at a thin gold foil and observing the scattering pattern on a fluorescent screen. The observations showed that most alpha particles passed through the foil undeflected, while a small fraction were scattered at large angles, suggesting that atoms have a concentrated positive charge (nucleus) surrounded by empty space and electrons.

The relationship between atomic number, mass number, isotopes, isobars, and valency of an atom is as follows: The atomic number (number of protons) determines the identity of the element, while the mass number (sum of protons and neutrons) represents different isotopes of the element. Isobars are atoms of different elements with the same mass number. Valency is determined by the number of electrons involved in chemical bonding, which can vary for different isotopes or elements.