MediumChemistryHigh School (9–10)GeneralThe Periodic Table › Groups and FamiliesConceptualBoard Exam
An element has the electron arrangement 2, 8, 18, 7…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
An element has the electron arrangement 2, 8, 18, 7. Say what you can about it: its period and group, its valency, whether it is a metal, the formula of its compound with sodium and with hydrogen, and its name.
Need a reminder? The key ideaShow
The position predicts the valency, the formulas, the reactivity and the nature of an element. A property in the middle of a group can be estimated as the average of its two neighbours, but only roughly.
The worked solution
Have you tried it?
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. Place. Four shells: period 4. Seven outer electrons: group 17.
Step 2. Valency. It gains one electron: valency .
Step 3. Nature. A halogen, so a non-metal.
Step 4. Formulas. With sodium: NaX. With hydrogen: HX.
Answer: period 4, group 17, valency , a non-metal; NaBr and HBr; it is bromine.
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