Question 12 For the covalent molecule, silicon tetrabromide. a. Draw the Lewis diagram. b. How many total valence electrons are present? c. How many bonding electron pairs? How many lone pairs does the central atom have? d. What is the molecular shape of the molecule? e. Is the molecule polar or nonpolar? f. What is the strongest attraction between molecules of silicon tetrabromide?

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**a. Lewis Diagram**  
Silicon tetrabromide, $$\text{SiBr}_4$$, has a silicon atom in the center connected via single bonds to four bromine atoms. Each bromine atom possesses three lone pairs of electrons. The diagram can be represented as:

$$
\begin{array}{c}
\quad :\! \text{Br} : \
\quad \quad \; \downarrow \
:\! \text{Br} - \text{Si} - \text{Br} : \
\quad \quad \; \uparrow \
\quad :\! \text{Br} : \
\end{array}
$$

Each bromine is drawn with three pairs of dots around it indicating its lone pairs, and silicon is connected to each bromine by single bonds.

**b. Total Valence Electrons**  
Silicon (Si) is in group 14 and contributes $$4$$ electrons. Bromine (Br) is in group 17 and contributes $$7$$ electrons each. With four bromine atoms, the total electrons are calculated as:

$$
4 + 4 \times 7 = 4 + 28 = 32.
$$

So, there are $$32$$ total valence electrons present.

**c. Bonding Electron Pairs and Lone Pairs on the Central Atom**  
- **Bonding electron pairs:** There are four $$\text{Si–Br}$$ bonds, so there are $$4$$ bonding pairs.  
- **Lone pairs on the central atom (Si):** All $$4$$ of Si's valence electrons are used in bonding with the bromine atoms, so there are $$0$$ lone pairs on silicon.

**d. Molecular Shape**  
With four bonding pairs around the central silicon atom and no lone pairs, the VSEPR theory gives a tetrahedral molecular shape.

**e. Polarity**  
Even though each $$\text{Si–Br}$$ bond is polar (because bromine is more electronegative than silicon), the symmetric tetrahedral arrangement causes the bond dipoles to cancel out. Therefore, the molecule is **nonpolar**.

**f. Strongest Attraction Between Molecules**  
Since $$\text{SiBr}_4$$ is a nonpolar molecule, the only intermolecular forces present are **London dispersion forces** (induced dipole-induced dipole attractions), which are the strongest attractions between its molecules.
**a. Lewis Diagram** Silicon tetrabromide has a silicon atom in the center connected to four bromine atoms with single bonds. Each bromine has three lone pairs. **b. Total Valence Electrons** There are 32 total valence electrons. **c. Bonding and Lone Pairs** - 4 bonding pairs - 0 lone pairs on silicon **d. Molecular Shape** Tetrahedral **e. Polarity** Nonpolar **f. Strongest Attraction** London dispersion forces

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