→ Most electronegative element in period 3 is chlorine \(\ce{(Cl)}\).

→ The electronegativity is a measure of an atom’s ability to attract electrons to itself.

→ Electronegativities increase across periods in the periodic table from left to right or as the number of valence electrons increases.

→ Fluorine is the most electronegative element with all other electronegativities relative to this.

→ The Bohr model of the atom was developed to use the quantisation of energy to explain the emission and absorption spectrum of hydrogen.

→ It proposed that the single electron of the atom was confined to defined orbits around the nucleus, somewhat analogous to a planet’s orbit around its star.

→ For the electron to change to a different orbit, energy had to be absorbed (to go to a higher energy orbit) or emitted (to go to a lower energy orbit).

→ The energy absorbed or emitted is well-defined, giving rise to sharp absorption or emission lines. No other changes in energy are allowed.

→ The model was an important step towards understanding and accepting the quantum view of the atom and introduced the idea of energy levels (shells) to describe the electronic configuration of atoms.

→ The Bohr model could not be applied to atoms other than hydrogen and did not provide any explanation for the quantisation.

→ These restrictions and limitations of the model were recognised by Bohr and the model was not meant to be used beyond the hydrogen atom, but the attractiveness of the simplicity of the model has ensured continued use and propagates the incorrect concept of electrons as particles orbiting a nucleus.