Question

Mendeleev’s principle of chemical periodicity states that when the elements are arranged according to their atomic numbers. This periodic law allows elements with similar properties to appear at regular intervals. Predict the group of elements and their number of valence electrons that will combine in a 2:1 ratio to with sodium. A)
bromine, chlorine, iodine, 7
B)
sulfur, selenium, polonium, 6
Eliminate
C)
hydrogen, fluorine, potassium, 1
D)
calcium, phosphorus, tellurium, 2

Answer 1

The main part of this question is the "2:1 ratio."

On the periodic table, bromine, chlorine, and iodine have 7 valence electrons and sulfur, selenium, and polonium have 6, so these choices are viable based on their valence electrons. However, fluorine does not have 1 valence electron and phosphorus and tellurium do not have 2 valence electrons, so C) and D) are automatically out, leaving A) and B).

If we know that the sodium will combine in a 2:1 ratio, we know that the charge of the ions must have a 2:1 ratio too; that's how ionic compounds work. Sodium (Na) has an ion with a charge of +1 (Na+), so that means whatever ion it combines with in a 2:1 ratio must have a charge of -2   -   a 2:1 ratio.

Bromine, chlorine, and iodine have a charge of -1, but sulfur, selenium, and polonium have charges of -2. This gives us the correct answer as C).

Answer 2

The correct option is B.

Sodium will react with elements in GROUP 6, WHICH HAVE SIX ELECTRONS IN THEIR OUTERMOST SHELLS.

Sodium is a metal with atomic number 11. The electronic configuration of sodium is 2,8,1. This implies that, sodium has one electron in its outermost shell. Sodium always donate this electron in order to become stable. Elements in group 6 have six electrons in their outermost shells and they require two more electrons to attain stability. In order to form chemical bonds with elements from group 6, two atoms of sodium will react with each atom of those elements, that is, the ratio of reaction will be 2:1. By so doing, the two sodium atoms will be the ones that will donate the two electrons that the group 6 elements need to attain stability. One example of compounds formed by such reaction is sodium sulfide, Na2S.