Question

which of the following electron configurations represents an element with similar chemical properties to an element with the electron configuration of 1s²2s¹?
1s²2s²2p⁵
1s²2s²2p⁶
1s²2s²2p⁶3s²3p⁵
1s²2s²2p⁶3s²3p⁶4s¹
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶

Explanation:

Step1: Understand the key - outer electron configuration

Elements with similar chemical properties have similar outer - shell electron configurations. The given electron configuration $1s^{2}2s^{1}$ has 1 electron in its outermost shell (the 2s orbital).

Step2: Analyze each option's outer - shell electrons

• For $1s^{2}2s^{2}2p^{5}$, the outer - shell has 7 electrons ($2s^{2}2p^{5}$).
• For $1s^{2}2s^{2}2p^{6}$, the outer - shell has 8 electrons ($2s^{2}2p^{6}$).
• For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$, the outer - shell has 7 electrons ($3s^{2}3p^{5}$).
• For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}$, the outer - shell has 1 electron ($4s^{1}$), which is similar to the given configuration's outer - shell electron count.
• For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}$, the outer - shell has 8 electrons ($4s^{2}4p^{6}$).

Answer:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}$