Chemistry · Atomic structure and the periodic table. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Elements in the modern periodic table are in order of atomic number. The group number gives the number of electrons in the outer shell and the period number gives the number of shells. Elements in a group react in similar ways because they have the same number of outer electrons. Metals are on the left and form positive ions. Non-metals are on the right.
Mendeleev ordered the elements mainly by atomic weight. He left gaps for elements not yet discovered and changed the order of some pairs so that their properties matched.
Group 0 atoms have full outer shells, so they are unreactive. Group 1 metals get more reactive down the group. Group 7 non-metals get less reactive down the group.
Students give Group 7 the same reactivity trend as Group 1. The trends are opposite: Group 1 gets more reactive down the group, Group 7 gets less reactive.
Answer: Yes. Iodine forms, so the solution turns brown.
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