Question

question 6 of 25
what is the electron configuration for la (lanthanum)?
a. kr6s²5d¹
b. xe6s²5d¹
c. cs6s²5d¹
d. rn6s²5d¹

Explanation:

Step1: Recall noble - gas shorthand rules

Noble - gas shorthand uses the electron configuration of the nearest noble gas with a lower atomic number. Lanthanum (La) has an atomic number of 57.

Step2: Identify the nearest noble gas

The nearest noble gas with an atomic number lower than 57 is xenon (Xe), which has an atomic number of 54.

Step3: Write the remaining electrons

After using the [Xe] core, we need to account for the remaining 3 electrons. The electron configuration of La follows the pattern of filling the 6s and 5d orbitals. The 6s orbital fills before the 5d orbital. So, the electron configuration of La is [Xe]6s²5d¹.

Answer:

B. [Xe]6s²5d¹