Question

helium (he) has two valence electrons, and these electrons are located in the 1s subshell. without using the periodic table, in which group and period is helium located?
group 8a, period 1
group 6a, period 3
group 3b, period 6
group 3a, period 3
question 20
1 pts
which group has seven valence electrons?
halogens
noble gases
alkaline earth metals
alkali metals

Explanation:

1. Helium has two valence - electrons and its electrons are in the 1s subshell. The period number is determined by the principal quantum number of the outermost shell (n = 1 for helium, so period 1). Helium is a noble gas and is placed in Group 8A (even though it has only 2 valence electrons, it has a full outer - shell configuration).
2. Halogens have seven valence electrons. Noble gases have 8 (except helium which has 2), alkaline earth metals have 2, and alkali metals have 1.

Answer:

1. Group 8A, Period 1
2. halogens