Refer to pages 79 and 81 of the Formulae and Tables booklet when answering this question - Leaving Cert Chemistry - Question 5 - 2022

The type of bonding that arises when atoms share electrons is called covalent bonding.

Yes, when two hydrogen atoms join to form a H₂ molecule, each H atom achieves a noble gas arrangement of electrons, effectively having a full shell of 2 electrons.

The octet rule is not applicable to hydrogen atoms, as they can only accommodate a maximum of 2 electrons in their valence shell. Thus, in the case of H₂, the electron configuration is satisfied with 2 electrons.

Electronegativity is the relative measure of attraction or tendency of an atom to attract shared pairs of electrons in a covalent bond.

Sodium (Na) has the electron configuration:

• Level 1: 2 electrons
• Level 2: 8 electrons
• Level 3: 1 electron

Written as: $2, 8, 1$.

Fluorine (F) has the electron configuration:

• Level 1: 2 electrons
• Level 2: 7 electrons

Written as: $2, 7$.

In sodium fluoride (NaF), sodium has a lower electronegativity value compared to fluorine. The electron is transferred from sodium ion (Na⁺) to a fluorine atom (F), leading to ionic bonding.

The bonding in NaF arises through the transfer of an electron from sodium (which loses an electron and becomes Na⁺) to fluorine (which gains an electron to become F⁻). This results in the formation of oppositely charged ions, which are held together by electrostatic forces.

In an ammonia (NH₃) molecule, there are three pairs of bonding electrons around the nitrogen atom.

The shape of an NH₃ molecule is trigonal pyramidal.