Question

low energy to high energy-order of filling
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d

electron configurations – shorthand notation
as atoms get larger and their electron configurations become longer and longer, they can be expressed in
a shorthand notation which denotes their noble gas core.
example - the electron configuration of calcium (z = 20) is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$.
because $1s^2 2s^2 2p^6 3s^2 3p^6$ is the electron configuration of argon, shorthand is $ar 4s^2$.
write the ground state electron configuration in shorthand notation for:
scandium

iron

gallium

cadmium

lead

tennessine

Explanation:

Step1: Find noble gas core for Scandium

Scandium (Z=21) has noble gas core [Ar] (Z=18). Remaining electrons: $21-18=3$. Fill 4s then 3d: $4s^23d^1$.

Step2: Shorthand for Scandium

Combine core and valence: $[Ar]4s^23d^1$

Step3: Find noble gas core for Iron

Iron (Z=26) has noble gas core [Ar] (Z=18). Remaining electrons: $26-18=8$. Fill 4s then 3d: $4s^23d^6$.

Step4: Shorthand for Iron

Combine core and valence: $[Ar]4s^23d^6$

Step5: Find noble gas core for Gallium

Gallium (Z=31) has noble gas core [Ar] (Z=18). Remaining electrons: $31-18=13$. Fill 4s, 3d, then 4p: $4s^23d^{10}4p^1$.

Step6: Shorthand for Gallium

Combine core and valence: $[Ar]4s^23d^{10}4p^1$

Step7: Find noble gas core for Cadmium

Cadmium (Z=48) has noble gas core [Kr] (Z=36). Remaining electrons: $48-36=12$. Fill 5s then 4d: $5s^24d^{10}$.

Step8: Shorthand for Cadmium

Combine core and valence: $[Kr]5s^24d^{10}$

Step9: Find noble gas core for Lead

Lead (Z=82) has noble gas core [Xe] (Z=54). Remaining electrons: $82-54=28$. Fill 6s, 4f, 5d, then 6p: $6s^24f^{14}5d^{10}6p^2$.

Step10: Shorthand for Lead

Combine core and valence: $[Xe]6s^24f^{14}5d^{10}6p^2$

Step11: Find noble gas core for Tennessine

Tennessine (Z=117) has noble gas core [Rn] (Z=86). Remaining electrons: $117-86=31$. Fill 7s, 5f, 6d, then 7p: $7s^25f^{14}6d^{10}7p^5$.

Step12: Shorthand for Tennessine

Combine core and valence: $[Rn]7s^25f^{14}6d^{10}7p^5$

Answer:

Scandium: $\boldsymbol{[Ar]4s^23d^1}$
Iron: $\boldsymbol{[Ar]4s^23d^6}$
Gallium: $\boldsymbol{[Ar]4s^23d^{10}4p^1}$
Cadmium: $\boldsymbol{[Kr]5s^24d^{10}}$
Lead: $\boldsymbol{[Xe]6s^24f^{14}5d^{10}6p^2}$
Tennessine: $\boldsymbol{[Rn]7s^25f^{14}6d^{10}7p^5}$