- Use Lewis dot symbols to show the sharing of electrons between two bromine atoms to form a bromine (Br2) molecule. Label all electron pairs as bonding pairs (BPs) or lone pairs (LPs).
- Use Lewis dot symbols to show the sharing of electrons between a phosphorus atom and hydrogen atoms to form a molecule in which phosphorus has an octet of electrons.
The Correct Answer and Explanation is :
1. Bromine Molecule (Br₂)
In a bromine (Br₂) molecule, two bromine atoms share electrons to form a covalent bond. Each bromine atom in the molecule has seven valence electrons, as shown in its Lewis dot structure:
- Step 1: Each bromine atom has seven valence electrons. The dot symbol for each bromine atom looks like this:
[ \text{Br} \cdot \text{Br} ] The dots represent the valence electrons around each bromine atom. - Step 2: When two bromine atoms bond to form Br₂, one electron from each bromine atom will be shared, creating a covalent bond. This shared pair of electrons forms the bond between the two atoms.
- Step 3: After the bonding, both bromine atoms will have a complete octet (8 electrons), as they each share one electron from the other atom. The final Lewis structure for Br₂ is:
[
\text{Br} : \text{Br}
]
This structure shows that each bromine atom has six electrons as lone pairs (LP) and two electrons in the bonding pair (BP).
Labeling:
- Lone pairs (LP) on each bromine atom: 6 electrons per atom (3 pairs of dots)
- Bonding pairs (BP): 1 pair of shared electrons (1 dash between the two Br atoms)
Final structure:
[
\text{Br} : \text{Br}
]
2. Phosphorus Hydride (PH₃)
In phosphorus hydride (PH₃), phosphorus shares electrons with hydrogen atoms to form a molecule where phosphorus achieves an octet.
- Step 1: Phosphorus has five valence electrons, and hydrogen has one valence electron. The dot structure for phosphorus and hydrogen is:
[
\text{H} \cdot, \, \text{P} \cdot \cdot \cdot \cdot
] - Step 2: To form PH₃, phosphorus shares one electron with each hydrogen atom. Since hydrogen only needs two electrons to fill its valence shell, each hydrogen shares one electron with phosphorus, and phosphorus shares one electron with each hydrogen.
- Step 3: After the bonding, phosphorus will have eight electrons in its valence shell (an octet). The final structure for PH₃ is:
[
\text{H} – \text{P} – \text{H}
]
[
\quad \ \ \ \text{H}
]
Labeling:
- Lone pairs (LP) on phosphorus: 1 lone pair (2 electrons)
- Bonding pairs (BP): 3 bonding pairs (each sharing one pair of electrons with hydrogen)
Final structure:
[
\text{H} – \text{P} – \text{H}
\quad \ \ \ \text{H}
]
In this structure, phosphorus fulfills the octet rule with a total of 8 electrons: 3 bonding pairs and 1 lone pair. Each hydrogen atom has 2 electrons, satisfying its duet rule.