The diagram shows a small part of a sodium chloride (NaCl) crystal, made up of sodium ions and chloride ions electrostatically attracted to each other - Leaving Cert Chemistry - Question 5 - 2015

The electron configuration of a sodium atom is 2 electrons in the first shell and 8 electrons in the second shell, with 1 electron in the outermost shell.

    2
  ______
 |      |
 |  8   |  1
 |______|

A sodium atom becomes a sodium ion by losing one electron from its outermost shell. This loss creates a positive charge, resulting in a sodium ion (Na⁺) with a configuration resembling that of neon.

The distribution of electrons in a chlorine atom is as follows: 2 electrons in the first shell, 8 electrons in the second shell, and 7 electrons in the outermost shell.

    2
  ______
 |      |
 |  8   |  7
 |______|

A chlorine atom becomes a chloride ion by gaining one electron, which gives it a negative charge. This new electron fulfills the outer shell, resulting in a chloride ion (Cl⁻) with a stable electron configuration similar to argon.

Chlorine atoms are smaller than sodium atoms because chlorine has more protons (17) in its nucleus, creating a stronger nuclear charge. This pulls the electrons closer to the nucleus, resulting in a smaller atomic radius compared to sodium, which has 11 protons.

Electronegativity is defined as the tendency of an atom to attract electrons towards itself when it is involved in a chemical bond. It is typically measured on the Pauling scale.

In a water molecule (H₂O), the electronegativity values of oxygen (approximately 3.44) and hydrogen (approximately 2.20) indicate a significant difference. This difference leads to polar covalent bonding, with oxygen being more electronegative and attracting the shared electrons more than hydrogen.

Sodium chloride can be dissolved in water due to the polar nature of water molecules. The positive side of water molecules is attracted to chloride ions (Cl⁻), while the negative side is attracted to sodium ions (Na⁺). This interaction facilitates the breakdown of the ionic lattice structure and disperses the ions in the solution.

A sodium chloride solution conducts electricity because the dissolved ions (Na⁺ and Cl⁻) are free to move in the solution. When an electric field is applied, these ions can migrate, allowing the solution to conduct an electric current.