How many valence shell electrons does an atom of thallium have?
The Correct Answer and Explanation is :
Thallium (( \text{Tl} )) has three valence electrons in its outermost shell.
Explanation:
Thallium is an element in Group 13 of the periodic table, also known as the boron group. The electron configuration of thallium is:
[ \text{Tl}: [\text{Xe}] 4f^{14} 5d^{10} 6s^2 6p^1 ]
To determine the number of valence electrons, we focus on the outermost electron shell, which in thallium’s case is the sixth shell ((n=6)). The electrons in the (6s) and (6p) orbitals are part of this shell:
- (6s^2): two electrons
- (6p^1): one electron
Adding these together gives a total of three valence electrons.
Key Points:
- Valence electrons are the electrons in the outermost electron shell of an atom. These are the electrons involved in chemical bonding.
- Thallium belongs to Group 13, where all elements typically have three valence electrons. This group trend is due to the presence of two (s)-electrons and one (p)-electron in their outermost shell.
- Although thallium has filled (4f)- and (5d)-subshells, these electrons are not considered valence electrons because they reside in inner shells and do not participate directly in chemical bonding.
- Thallium’s chemistry is interesting because it can exhibit multiple oxidation states. The +1 oxidation state is more common than the expected +3, due to the “inert pair effect.” This effect arises because the (6s^2) electrons are more stable and less likely to participate in bonding, leaving the (6p^1) electron to bond.
Thus, while thallium has three valence electrons, its chemical behavior often reflects the involvement of only one electron from its (6p)-subshell.