Which element can expand its valence shell to accommodate more than eight electrons?

Phosphorous

Explanation:

The octet rule states that atoms below atomic number 20 on the periodic table, tend to combine so that they each have eight electrons in their valence shells, which allows them to have identical electronic configuration as a noble gas.

Phosphorous is, known to be highly reactive; it has the ability to bend the octet rule and expand its valence shell to allow more than eight (8) electrons. Sulphur is another example of an element that accommodates more than 8 electrons.