Question

use the periodic table and your knowledge of atomic structure to match each element with the correct electron configuration.
arsenic (as)
phosphorus (p)
chromium (cr)
chlorine (cl)
sodium (na)
1s²2s²2p⁶3s¹
1s²2s²2p⁶3s²3p⁶4s²3d⁴
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p³
1s²2s²2p⁶3s²3p³
1s²2s²2p⁶3s²3p⁵

Explanation:

Step1: Recall electron - configuration rules

Electrons fill orbitals in the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p etc. The number of electrons in each sub - shell is given by the exponent.

Step2: Analyze sodium (Na)

Sodium has an atomic number of 11. Its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{1}$.

Step3: Analyze phosphorus (P)

Phosphorus has an atomic number of 15. Its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}$.

Step4: Analyze chlorine (Cl)

Chlorine has an atomic number of 17. Its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$.

Step5: Analyze arsenic (As)

Arsenic has an atomic number of 33. Its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$.

Step6: Analyze chromium (Cr)

Chromium has an atomic number of 24. Due to the stability of half - filled d - orbitals, its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5}$ (not the expected $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{4}$). But among the given configurations, the closest one for the elements presented is:

• Sodium (Na) matches $1s^{2}2s^{2}2p^{6}3s^{1}$
• Phosphorus (P) matches $1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}$
• Chlorine (Cl) matches $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$
• Arsenic (As) matches $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$

Answer:

Sodium (Na) - $1s^{2}2s^{2}2p^{6}3s^{1}$
Phosphorus (P) - $1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}$
Chlorine (Cl) - $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$
Arsenic (As) - $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$