Which is the electron configuration for lithium?
A. $1 s^2$
B. $2 s^3$
C. $1 s^2 2 s^1$
D. $1 s^1 2 s^2$
Answer (1)
Lithium has 3 electrons.
The first 2 electrons fill the 1 s subshell: 1 s 2 .
The remaining electron occupies the 2 s subshell: 2 s 1 .
The electron configuration for lithium is 1 s 2 2 s 1 .
Explanation
Determine the number of electrons Lithium has an atomic number of 3, which means a neutral lithium atom has 3 electrons. We need to determine how these electrons are arranged in the electron shells and subshells.
Fill the first electron shell The first electron shell (n=1) has only one subshell, the 1s subshell, which can hold up to 2 electrons. So, the first two electrons of lithium will fill the 1s subshell, resulting in a 1 s 2 configuration.
Fill the second electron shell After filling the 1s subshell with 2 electrons, we have 1 electron remaining. This electron will go into the next available subshell, which is the 2s subshell in the second electron shell (n=2). The 2s subshell can hold up to 2 electrons, but we only have 1 electron left, so it will be 2 s 1 .
Write the electron configuration Combining the configurations of the first and second shells, the electron configuration for lithium is 1 s 2 2 s 1 .
Examples
Understanding electron configurations is crucial in chemistry for predicting how elements will interact to form chemical bonds. For example, knowing that lithium has a 1 s 2 2 s 1 configuration helps us understand that it readily loses one electron to form a positive ion, L i + , which can then bond with other elements like fluorine to form lithium fluoride, L i F . This concept is fundamental in designing new materials and understanding chemical reactions.
