The shape of chromate ion is

Options

A. tetrahedral
B. square planar
C. two tetrahydra linked at one of their apex
D. octahedral

Answer

To determine the shape of the chromate ion (CrO4^2-), we can follow these steps:

### Step 1: Identify the central atom and its oxidation state
The central atom in the chromate ion is chromium (Cr). In the chromate ion, chromium has an oxidation state of +6.

**Hint:** Remember that the oxidation state of the central atom can help you determine the number of bonds it can form.

### Step 2: Count the number of valence electrons
Chromium has 6 valence electrons, and each oxygen atom has 6 valence electrons. Since there are four oxygen atoms, the total number of valence electrons contributed by oxygen is 4 × 6 = 24. However, we need to account for the 2 negative charges on the chromate ion, which adds 2 more electrons. Therefore, the total number of valence electrons is:

\[ 6 (from \, Cr) + 24 (from \, O) + 2 (for \, charges) = 32 \, electrons \]

**Hint:** When calculating total valence electrons, remember to include those contributed by the charge of the ion.

### Step 3: Determine the number of bonds and lone pairs
To form the chromate ion, chromium will form double bonds with some of the oxygen atoms and single bonds with others. The structure can be represented as:

- One Cr=O double bond (1 oxygen)
- Three Cr-O single bonds (3 oxygens)

This results in a total of 4 bonds (1 double bond and 3 single bonds) and no lone pairs on the central atom.

**Hint:** Visualizing the Lewis structure can help you see how many bonds and lone pairs are present.

### Step 4: Use VSEPR theory to determine the shape
According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the shape of a molecule is determined by the repulsion between electron pairs. With 4 bonding pairs and no lone pairs, the chromate ion adopts a tetrahedral shape.

**Hint:** VSEPR theory is a useful tool for predicting molecular geometry based on the number of bonding and lone pairs around the central atom.

### Conclusion
The shape of the chromate ion (CrO4^2-) is tetrahedral.

**Final Answer:** The shape of the chromate ion is tetrahedral.

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