In terms of chemical bonding, which type of bond is primarily found in solid sodium bromide (NaBr)?

Introduction / Context:
Sodium bromide, NaBr, is a simple binary compound of a metal and a nonmetal. Classifying the bond type in such compounds helps students understand how structure relates to properties like melting point, solubility and conductivity. This question asks which type of bond is primarily present in solid sodium bromide. Recognising ionic versus covalent bonding is a fundamental skill in introductory chemistry.

Given Data / Assumptions:

• Compound: sodium bromide, NaBr.
• Sodium is an alkali metal in group 1 of the periodic table.
• Bromine is a halogen in group 17.
• The solid is a crystalline salt at room temperature.

Concept / Approach:
When a highly electropositive metal such as sodium combines with a highly electronegative nonmetal such as bromine, the metal tends to lose an electron to form a cation, and the nonmetal tends to gain an electron to form an anion. In NaBr, sodium loses one electron to form Na⁺ and bromine gains one electron to form Br⁻. The electrostatic attraction between these oppositely charged ions produces an ionic crystal lattice. This is quite different from covalent bond formation, where electrons are shared between atoms, and from metallic bonding, which involves a sea of delocalised electrons in a metal lattice.

Step-by-Step Solution:
Step 1: Identify sodium as a group 1 metal, which commonly forms Na⁺ ions by losing one valence electron. Step 2: Identify bromine as a halogen, which commonly gains one electron to form Br⁻ ions. Step 3: Recognise that Na⁺ and Br⁻ combine due to electrostatic attraction, forming an extended ionic lattice rather than discrete molecules. Step 4: The dominant bond type in such a lattice is ionic bonding between positive and negative ions. Step 5: Therefore, the primary bond in sodium bromide is ionic, not covalent, metallic or hydrogen bonding.

Verification / Alternative check:
Physical properties of NaBr support the ionic bonding model. Sodium bromide has a relatively high melting point and conducts electricity when molten or dissolved in water, indicating the presence of mobile ions. It is also readily soluble in water, forming an electrolyte solution. These characteristics are typical of ionic salts. In contrast, covalent molecular substances often have lower melting points and do not conduct electricity in solution in the same way.

Why Other Options Are Wrong:
Option B, covalent bonding, is more typical of compounds formed between nonmetals, not between an alkali metal and a halogen. Option C, polar covalent bonds within discrete molecules, would describe compounds like HCl gas rather than ionic salts such as NaBr, which form lattices instead of individual molecules. Option D, metallic bonding, occurs in pure metals and alloys, not in salts of metals with nonmetals. Option E, hydrogen bonding, requires hydrogen bonded to highly electronegative atoms like O, N or F; NaBr contains no hydrogen and cannot form hydrogen bonds. Only option A correctly identifies ionic bonding between Na⁺ and Br⁻ ions as the primary bond type in sodium bromide.

Common Pitfalls:
A common mistake is to think that all halogen containing compounds are covalent because examples like HCl and Cl2 are taught early. However, when halogens bond with very reactive metals such as sodium and potassium, ionic salts are formed. Another pitfall is to confuse polar covalent and ionic bonding; remembering the combination of metal with nonmetal, especially group 1 metals with group 17 nonmetals, is a good cue for ionic character.

Final Answer:
The correct bond type is Ionic bond between Na⁺ and Br⁻ ions, which dominates in the crystal structure of solid sodium bromide.