Question

1. draw the orbital diagrams and electron configurations of the following elements.

a. mg
b. c
c. as
d. s²⁻

1. identify the following atoms and highlight/underline their valence electrons.

a. 1s²2s²2p⁶3s²3p³
b. 1s²2s²2p⁶3s²3p⁶4s²3d⁷
c. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹

Explanation:

Question 21:

Step1: Find atomic number

For each species, get atomic number (Z) from periodic table:

• Mg: Z=12; C: Z=6; As: Z=33; S²⁻: S has Z=16, +2 electrons = 18 total electrons.

Step2: Apply Aufbau principle

Fill orbitals in order: $1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p$

Step3: Write electron config

Orbital diagrams use boxes for orbitals, arrows for electrons (Pauli exclusion, Hund's rule).

a. Mg

Electron configuration: $1s^22s^22p^63s^2$
Orbital diagram:
$1s$: $\uparrow\downarrow$; $2s$: $\uparrow\downarrow$; $2p$: $\uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow$; $3s$: $\uparrow\downarrow$

b. C

Electron configuration: $1s^22s^22p^2$
Orbital diagram:
$1s$: $\uparrow\downarrow$; $2s$: $\uparrow\downarrow$; $2p$: $\uparrow\ \ \ \uparrow\ \ \ \ \ $

c. As

Electron configuration: $1s^22s^22p^63s^23p^64s^23d^{10}4p^3$
Orbital diagram:
$1s$: $\uparrow\downarrow$; $2s$: $\uparrow\downarrow$; $2p$: $\uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow$; $3s$: $\uparrow\downarrow$; $3p$: $\uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow$; $4s$: $\uparrow\downarrow$; $3d$: $\uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow$; $4p$: $\uparrow\ \ \ \uparrow\ \ \ \ \uparrow$

d. S²⁻

Electron configuration: $1s^22s^22p^63s^23p^6$
Orbital diagram:
$1s$: $\uparrow\downarrow$; $2s$: $\uparrow\downarrow$; $2p$: $\uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow$; $3s$: $\uparrow\downarrow$; $3p$: $\uparrow\downarrow\ \ \uparrow\downarrow\ \ \uparrow\downarrow$

1. Sum electrons to find atomic number, match to element. Valence electrons are in the highest principal energy level.
2. For transition metals, valence electrons include ns and (n-1)d electrons.

Answer:

a. Mg: Electron configuration: $\boldsymbol{1s^22s^22p^63s^2}$; Orbital diagram: $1s: \uparrow\downarrow,\ 2s: \uparrow\downarrow,\ 2p: \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow,\ 3s: \uparrow\downarrow$
b. C: Electron configuration: $\boldsymbol{1s^22s^22p^2}$; Orbital diagram: $1s: \uparrow\downarrow,\ 2s: \uparrow\downarrow,\ 2p: \uparrow\ \ \uparrow\ \ \ \ $
c. As: Electron configuration: $\boldsymbol{1s^22s^22p^63s^23p^64s^23d^{10}4p^3}$; Orbital diagram: $1s: \uparrow\downarrow,\ 2s: \uparrow\downarrow,\ 2p: \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow,\ 3s: \uparrow\downarrow,\ 3p: \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow,\ 4s: \uparrow\downarrow,\ 3d: \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow,\ 4p: \uparrow\ \ \uparrow\ \ \uparrow$
d. S²⁻: Electron configuration: $\boldsymbol{1s^22s^22p^63s^23p^6}$; Orbital diagram: $1s: \uparrow\downarrow,\ 2s: \uparrow\downarrow,\ 2p: \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow,\ 3s: \uparrow\downarrow,\ 3p: \uparrow\downarrow\ \uparrow\downarrow\ \uparrow\downarrow$

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Question 22: