What is the systematic name for Li2Cr2O7? What is the ionic charge on Cr?
The correct answer and explanation is :
Systematic name of Li₂Cr₂O₇:
Lithium dichromate
Ionic charge on Cr in Li₂Cr₂O₇:
Chromium (Cr) has an oxidation state of +6 in lithium dichromate.
Explanation (about 300 words):
Lithium dichromate, Li₂Cr₂O₇, is an ionic compound composed of lithium ions (Li⁺) and the dichromate ion (Cr₂O₇²⁻).
Step 1: Understanding the compound components
- Lithium (Li) is an alkali metal in Group 1 of the periodic table and almost always forms a +1 ion (Li⁺).
- The compound formula shows two lithium atoms: Li₂, meaning there are two Li⁺ ions contributing a total positive charge of +2.
Step 2: The anion – dichromate ion (Cr₂O₇²⁻)
- The anion in the compound is the dichromate ion, Cr₂O₇²⁻.
- The charge on the dichromate ion is known to be -2 overall.
Step 3: Determining the oxidation state of chromium
- Oxygen in almost all compounds has an oxidation state of -2.
- There are seven oxygen atoms in the dichromate ion, so total oxygen charge = 7 × (-2) = -14.
- The overall charge on the dichromate ion is -2.
- Let the oxidation state of chromium be $x$. Since there are two chromium atoms, their combined charge is $2x$.
Using the oxidation state rule:
$2x + (-14) = -2$
Simplify:
$2x – 14 = -2$
$2x = -2 + 14 = 12$
$x = \frac{12}{2} = +6$
Thus, each chromium atom has an oxidation state of +6.
Step 4: Naming the compound
- The cation is lithium: lithium
- The anion is dichromate, which is a common polyatomic ion derived from chromium and oxygen.
- The systematic name combines the cation and the anion: lithium dichromate.
Summary:
- The compound is composed of 2 Li⁺ ions and 1 dichromate ion (Cr₂O₇²⁻).
- Chromium in dichromate is in the +6 oxidation state.
- The systematic name is lithium dichromate.