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Chapter 7: Problem 68

Consider the dichromate ion. It has no metal-metal nor oxygenoxygen bonds. Write a Lewis structure for the dichromate ion. Consider chromium to have six valence electrons.

Short Answer

Expert verified
Answer: The Lewis structure for the dichromate ion is as follows: O O \\ // Cr - O - Cr // \\ O O \\ / O - - O With a -2 charge on the top and bottom single-bonded oxygen atoms.

Step by step solution

01

Determine the elements and their charges

The dichromate ion is Cr2O7^2-. There are two chromium atoms (Cr) with six valence electrons each and seven oxygen atoms (O) with six valence electrons each. The overall charge of this ion is -2.
02

Calculate the total number of valence electrons

We need to find the total number of valence electrons in the system. Total valence electrons = (2 Chromium x 6 electrons) + (7 Oxygen x 6 electrons) + 2 extra electrons (due to 2- charge) = 12 + 42 + 2 = 56 electrons
03

Draw the skeletal structure

There are two chromium atoms, and each of them will be bonded to four oxygen atoms. In the skeletal structure, each chromium atom is attached to two oxygen atoms with single bonds and another two oxygen atoms with double bonds. Place the two extra negatively charged electrons on a single bonded oxygen.
04

Place the electrons around each atom

Now, distribute the remaining electrons among the atoms in the ion, providing each atom with an octet, including the extra negatively charged electrons in the ion. Start by adding lone pairs of electrons to the single bonded oxygen atoms (6 each, after accounting for the negatively charged electrons). Then, double bond each chromium atom with two other oxygen atoms (4 each).
05

Verify the octet rule and overall charge

After assigning all the electrons, check that each atom satisfies the octet rule (8 electrons in the valence shell) and that the overall charge of the ion is -2. We can see that each oxygen atom has 8 electrons, and each chromium atom has 12 electrons, which is acceptable for transition metals. The overall charge of the setup is -2, as required. The final Lewis structure for the dichromate ion is: O O \\ // Cr - O - Cr // \\ O O \\ / O - - O Note the -2 charge on the top and bottom single-bonded oxygen.

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Most popular questions from this chapter

Give the formula of a polyatomic ion that you would expect to have the same Lewis structure as (a) \(\mathrm{Cl}_{2}\) (b) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{CH}_{4}\) (d) \(\mathrm{GeCl}_{4}\)

Radioastronomers have detected the isoformyl ion, \(\mathrm{HCO}^{\top}\), in outer space. Write the Lewis structure for this ion.

Predict the geometry of the following species: (a) \(\mathrm{SCO}\) (b) \(\mathrm{IBr}_{2}^{-}\) (c) \(\mathrm{NO}_{3}^{-}\) (d) \(\mathrm{RnF}_{4}\)

In each of the following polyatomic ions, the central atom has an expanded octet. Determine the number of electron pairs around the central atom and the hybridization in (a) \(\mathrm{SF}_{2}{ }^{2-}\) (b) \(\mathrm{AsCl}_{6}^{-}\) (c) \(\mathrm{SCl}_{4}{ }^{2-}\)

Based on the concept of formal charge, what is the central atom in (a) HCN (do not include \(H\) as a possibility)? (b) \(\mathrm{NOCl}(\mathrm{Cl}\) is always a terminal atom)?
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