Question

Which element can expand its valence shell to accommodate more than eight electrons? which element can expand its valence shell to accommodate more than eight electrons? o he n br?

Answer 1

Answer:

Br can expand its valence shell to accommodate more than eight electrons.

Explanation:

In a bond, elements tends to accommodate their valence electrons to reach the configuration of a noble gas (The Octet rule), so they try to complete their valence shell with 8 electrons, and they can do that only if they use the orbitals s (may contain only 2 electrons) and p (may contain only 6 electrons).

Sometimes, there are elements that need to share more than 8 valence electrons to use all the available electrons, but this is possible only if the atom has orbitals d (may contain 10 electrons) or f (may contain 14 electrons).

That's why only the elements that has a number 3 of period or more can expand its valence shell, because level 3 atoms has a d subshell.

In this case, He atom is in period number 1, N atom is in period number 2 and Br atom is in period number 3, that's why Br atom can expand its valence shell, and He and N atoms can't.

Answer 2

According to octet rule,  atoms with an atomic number less than 20 tend to combine  with other atom such that both of these atoms have eight electrons in their valence shells, which gives them the same electronic configuration as that of noble gas.

However, there are few compound that donot obey octel rule. Among the elements mentioned above i.e. oxygen and helium obeys octet rule.

In case of nitrogen, oxide of nitrogen (like NO and NO2) have incomplete octet. 

While there are few compounds of Br wherein Br has expanded octet. For example, in BrF5, Br has 12 electrons in valence shell.