Step 1: Recall that for a neutral element, Atomic number = # of protons = # of electrons.
The atomic number of Cr is 24 which means Cr has 24 electrons.
The location of Cr in the periodic table is shown below:
Based on the figure, Cr belongs in the d-block in Period 4 so its electron configuration will contain the 4s and 3d subshells.
• s–subshell can hold a maximum of 2 electrons
• p–subshell can hold a maximum of 6 electrons
• d–subshell can hold a maximum of 10 electrons
• f–subshell can hold a maximum of 14 electrons
Starting from 1s, the electron configuration for Cr is:
Step 2: In ammonium chromate, the charge of Cr is +6.
The +6 charge means 6 e– were lost. Therefore, we need to subtract 3 e– starting from the highest energy level (4s).
The electron configuration for Cr6+ is:
How many unpaired electrons would you expect on chromium in ammonium chromate?
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