Lewis dot of MgBr
The phrase lewis dot of mg br commonly points to the ionic Lewis representation for magnesium bromide. Magnesium forms a stable cation with charge \(+2\), and bromine forms a stable anion with charge \(-1\), so the formula unit is \( \mathrm{MgBr_2} \).
Valence electrons and ion formation
Magnesium (Group 2) has 2 valence electrons and readily forms \(\mathrm{Mg^{2+}}\) by losing both. Bromine (Group 17) has 7 valence electrons and forms \(\mathrm{Br^-}\) by gaining 1 electron to complete an octet.
\[ \mathrm{Mg \rightarrow Mg^{2+} + 2e^-} \]
\[ \mathrm{2Br + 2e^- \rightarrow 2Br^-} \]
Ionic Lewis dot representation
The Lewis dot diagram for an ionic compound is written as ions in brackets with charges. The cation \(\mathrm{Mg^{2+}}\) carries no dots in the Lewis symbol because its valence shell electrons are lost. Each \(\mathrm{Br^-}\) is shown with eight electrons (four lone pairs) around the symbol.
A neutral “MgBr” unit would require \(\mathrm{Mg^+}\) paired with \(\mathrm{Br^-}\), which is not the typical stable ionic state for magnesium in general chemistry. Charge balance with \(\mathrm{Mg^{2+}}\) produces \( \mathrm{MgBr_2} \).
Compact summary table
| Species | Valence electrons (neutral atom) | Ion formed | Lewis dot meaning |
|---|---|---|---|
| Mg | 2 | \(\mathrm{Mg^{2+}}\) | No dots shown on \(\mathrm{Mg^{2+}}\); electrons transferred away |
| Br | 7 | \(\mathrm{Br^-}\) | Eight dots on \(\mathrm{Br^-}\); complete octet (four lone pairs) |
Visualization of electron transfer and the final ionic diagram
Common pitfalls
Bromine is often written as \(\mathrm{Br_2}\) in elemental form, yet the bromide ion in salts is \(\mathrm{Br^-}\). The Lewis dots for ionic compounds track electron transfer and octets on anions rather than shared pairs between atoms.