Which is the correct Lewis structure for magnesium bromide? a) 2 Mg²+ [Br] c) Mg²+2 [Br] b) Mg:Br: d) :Mg:Br:
The Correct Answer and Explanation is:
The correct Lewis structure for magnesium bromide (MgBr₂) is:
c) Mg²⁺ 2[B
Magnesium bromide is an ionic compound composed of magnesium (Mg) and bromine (Br) atoms. To determine its correct Lewis structure, we must consider the nature of the bonding and the electron configurations of the involved elements.
1. Ionic Nature of MgBr₂:
Magnesium is a group 2 element with an electron configuration of [Ne]3s². It has two valence electrons, which it readily loses to achieve a stable noble gas configuration like neon. Losing two electrons results in a Mg²⁺ cation.
Bromine is a group 17 (halogen) element with seven valence electrons. It needs one more electron to complete its octet. Each bromine atom gains one electron to become a Br⁻ anion.
2. Formation of MgBr₂:
For charge balance:
- One Mg atom loses 2 electrons to become Mg²⁺
- Two Br atoms each gain 1 electron to become 2Br⁻
The resulting compound is electrically neutral:
Mg²⁺ + 2Br⁻ → MgBr₂
3. Lewis Structure Representation:
In ionic compounds, the Lewis structure shows ions with full outer shells:
- Mg²⁺ is represented without valence electrons (it lost them).
- Br⁻ ions are shown with full octets (eight electrons around each).
Therefore, the correct Lewis structure is:
Mg²⁺ 2[Br⁻]
This matches option c), which shows the metal cation and two halide anions correctly.
4. Why Other Options Are Incorrect:
- a) “2 Mg²⁺ [Br]” implies two magnesium ions for one bromide—incorrect stoichiometry.
- b) “Mg:Br:” suggests covalent bonding—incorrect for an ionic compound.
- d) “:Mg:Br:” also suggests shared electrons (covalent)—not appropriate for MgBr₂.
Thus, option c) Mg²⁺ 2[Br⁻] is correct.
