Which pair of atoms is most likely to form an ionic bond based on their positions and typical behaviour in the periodic table?

Introduction / Context:
Ionic and covalent bonds are two major types of chemical bonding. Recognising which pair of elements will form which type of bond is a key general chemistry skill. Ionic bonds usually form between metals that readily lose electrons and non metals that readily gain electrons. This question asks you to identify the pair of atoms that is most likely to form an ionic bond, based on their typical positions and behaviour in the periodic table.

Given Data / Assumptions:

• We are comparing several pairs of elements, including sodium with chlorine and combinations of non metals.
• Ionic bonds involve significant electron transfer from one atom to another, creating oppositely charged ions.
• Covalent bonds involve sharing of electrons, usually between non metals.
• We assume normal room temperature conditions and standard oxidation states.

Concept / Approach:
A typical ionic bond forms when a highly electropositive metal from the left side of the periodic table transfers one or more electrons to a highly electronegative non metal from the right side. The resulting cation and anion attract each other strongly. Sodium is an alkali metal that easily loses one electron to form Na plus, and chlorine is a halogen that readily gains one electron to form Cl minus. The strong electrostatic attraction between Na plus and Cl minus gives the ionic compound sodium chloride. In contrast, pairs consisting only of non metals, such as H and O or C and H, normally form covalent bonds by sharing electrons rather than fully transferring them.

Step-by-Step Solution:
Step 1: Analyse sodium and chlorine. Sodium is in group 1 and easily loses an electron. Chlorine is in group 17 and readily gains an electron. This is ideal for ionic bonding. Step 2: Consider hydrogen and oxygen. Both are non metals and typically share electrons to form covalent O H bonds, for example in water. Step 3: Look at carbon and hydrogen. These form mainly covalent C H bonds in organic compounds. Step 4: Examine nitrogen and oxygen. Both are non metals and in compounds such as NO2 and N2O5 they share electrons covalently. Step 5: Review chlorine and bromine. Both are halogens, similar non metals that form covalent Cl Br bonds if combined. Step 6: Conclude that sodium and chlorine is the only pair that clearly fits the pattern of metal plus non metal forming an ionic bond.

Verification / Alternative check:
Sodium chloride is the classic textbook example of an ionic compound with a high melting point, crystalline lattice and strong electrostatic interactions between Na plus and Cl minus. The formation of NaCl can be described with the half reactions Na -> Na+ + e minus and Cl2 + 2e minus -> 2Cl minus. In contrast, water H2O, methane CH4 and nitrogen oxides are all described with covalent bonds and molecular structures. Observation of properties such as electrical conductivity when molten and high melting point further supports the ionic character of NaCl compared with molecular covalent compounds formed by the other pairs.

Why Other Options Are Wrong:
- Hydrogen and oxygen: These combine to form water with covalent bonds, not an ionic solid, under normal conditions.
- Carbon and hydrogen: The C H bonds in hydrocarbons are covalent, and no full electron transfer occurs between carbon and hydrogen.
- Nitrogen and oxygen: These both strongly attract electrons and share them in molecules, forming covalent bonds.
- Chlorine and bromine: Both are halogens; a Cl Br bond between them would be covalent rather than ionic.

Common Pitfalls:
Students sometimes assume that any two different elements can form ionic bonds, or they focus only on electronegativity without considering whether one partner is a metal. A simple rule of thumb is that ionic bonding is most likely between a group 1 or group 2 metal and a group 16 or group 17 non metal. When both partners are non metals, especially on the right side of the periodic table, covalent bonding is usually more appropriate. Remembering that sodium chloride is a classic ionic compound helps anchor this idea.

Final Answer:
The pair of atoms most likely to form an ionic bond is Sodium Na and chlorine Cl.