draw a Louis dot diagram for magnesium phosphide and phosphorus try hydride
Draw Lewis Dot diagrams for: explain briefly all 2 and explain it
a) Magnesium phosphide
b) Phosphorus trihydride.
The Correct Answer and Explanation is:
Let’s draw the Lewis Dot Diagrams for the following compounds and explain the bonding:
a) Magnesium Phosphide (Mg₃P₂)
Lewis Dot Diagram:
Mg has 2 valence electrons, and P has 5 valence electrons.
Each P³⁻ ion needs 3 electrons to complete its octet.
Each Mg atom loses 2 electrons to become Mg²⁺.
Thus:
- 3 Mg atoms lose a total of 6 electrons (3 × 2 = 6)
- 2 P atoms gain a total of 6 electrons (2 × 3 = 6)
This satisfies the charge balance:
3 Mg²⁺ + 2 P³⁻ → Mg₃P₂
We show this by:
- Writing Mg with no dots (they lose electrons).
- Writing P surrounded by 8 electrons, showing the gained 3 extra electrons from Mg.
Diagram:
Mg Mg Mg [••P••]³⁻ [••P••]³⁻
(no dots) (8 electrons around each P)
(Mg²⁺) (P³⁻ with octet completed)
b) Phosphorus Trihydride (PH₃)
Lewis Dot Diagram:
Phosphorus (P) = 5 valence electrons
Hydrogen (H) = 1 valence electron × 3 = 3 electrons
Phosphorus needs 3 electrons to form bonds with 3 H atoms and keeps one lone pair.
Diagram:
..
:P:
/ | \
H H H
- The “:” on top represents the lone pair of electrons on phosphorus.
- Each line (–) between P and H represents a single covalent bond (shared pair of electrons).
Explanation (300+ words):
Lewis Dot Structures are diagrams that represent the valence electrons of atoms and show how these electrons are involved in bonding. These diagrams help visualize how atoms come together to form molecules or ionic compounds by sharing or transferring electrons.
a) Magnesium Phosphide (Mg₃P₂):
This is an ionic compound, formed between magnesium (a metal) and phosphorus (a nonmetal). Magnesium atoms each lose two electrons, becoming Mg²⁺ ions. Phosphorus atoms each need to gain three electrons to achieve a stable octet, becoming P³⁻ ions. To balance charges:
- 3 Mg atoms lose 6 electrons (3 × 2 = 6),
- 2 P atoms gain 6 electrons (2 × 3 = 6),
making the formula Mg₃P₂ electrically neutral. In Lewis notation, we don’t show the lost electrons on Mg because metals donate them, and we draw full octets around P, with brackets and a charge of 3⁻.
b) Phosphorus Trihydride (PH₃):
This is a covalent compound, where phosphorus shares electrons with hydrogen. Phosphorus has 5 valence electrons and needs 3 more to complete its octet. Each hydrogen has 1 electron and needs 1 more. Phosphorus forms three single bonds with three hydrogen atoms, sharing a pair of electrons with each. The remaining two electrons on phosphorus remain as a lone pair, which affects the molecule’s geometry (trigonal pyramidal). The resulting molecule is neutral and stable. This type of bonding is typical for covalent molecules, where atoms achieve stability through electron sharing rather than transfer.
In conclusion, Mg₃P₂ is ionic with complete electron transfer, while PH₃ is covalent with electron sharing. Lewis Dot Diagrams are key to visualizing how these compounds form and help predict structure and behavior.