EasyChemistryHigh School (9–10)GeneralThe Periodic Table › Periodic TrendsStructure of the Atom › Electronic Configuration and ValencyNumerical
Selenium is in group 16, below sulphur. Its arrangement is 2, 8, 18, 6.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Selenium is in group 16, below sulphur. Its arrangement is 2, 8, 18, 6. Find its valency and the formula of its compound with hydrogen.
Need a reminder? The key ideaShow
Valency is the number of electrons an atom loses, gains or shares to fill its outer shell. With to outer electrons it equals that number; with to it is minus that number; a full shell gives . Cross the valencies to write a formula.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Outer electrons. Six.
Step 2. Valency. , like sulphur and oxygen above it.
Step 3. Hydride. Two hydrogens: , like and .
Answer: valency ; .
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