Question

electron configuration and atomic spectra - test
name: cristina garcia
the aufbau principle - the rule that tells you to fill the electrons from the lowest available orbital first before putting them in a higher energy orbital.
hunds rule - when you have more than one degenerate or same energy orbital, you place one electron into each. once each orbital has one electron, then you can start doubling up.
the pauli exclusion principle - no two electrons can share the same space in the exact same position. they must have opposite spins.
the electromagnetic spectrum
wavelength (meters)
radio 10³
cmb microwave 10⁻²
infrared 10⁻⁵
human sight visible 10⁻⁶
ultraviolet 10⁻⁸
x - ray 10⁻¹⁰
gamma ray 10⁻¹²
put the letter of the correct answer in the blank.

1. the neutral element with electron configuration 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵

(a) te (b) sr (c) br (d) as

1. what is the correct electron configuration for as?

(a) 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁴
(b) 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p³
(c) 1s²2s²2p⁶3s²3p⁶4s²4p⁶4d¹⁰5s²5p⁶5d³
(d) 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵5s²4d¹⁰5p³

1. what is the correct noble gas configuration for cobalt (co)?

(a) ar 4s²3d⁷ (b) ar 3d⁷ (c) ar 4s¹3d⁷ (d) ar 5s²4d⁷

1. which noble gas notations are correct for the elements given?

i. k: ne 3s²3p⁶4s¹
ii. y: kr 5s²4d¹
iii. sn: kr 5s²4d¹⁰5p²
(a) only i (b) i and ii and iii (c) i and iii (d) ii and iii

Explanation:

Step1: Determine element for first question

Count electrons in $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}$. Total electrons = 35. Bromine (Br) has 35 electrons.

Step2: Find As electron - configuration for second question

Arsenic (As) has atomic number 33. Using Aufbau principle, its electron - configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$.

Step3: Determine Co noble - gas configuration for third question

Cobalt (Co) has atomic number 27. Noble - gas core is argon (Ar, atomic number 18). Remaining electrons are 9, filled as $4s^{2}3d^{7}$. So, configuration is $[Ar]4s^{2}3d^{7}$.

Step4: Check noble - gas notations for fourth question

• For K (potassium, atomic number 19), noble - gas core should be [Ar] not [Ne]. Correct is $[Ar]4s^{1}$.
• For Y (yttrium, atomic number 39), noble - gas core is [Kr] and remaining electrons are filled as $5s^{2}4d^{1}$, so $[Kr]5s^{2}4d^{1}$ is correct.
• For Sn (tin, atomic number 50), noble - gas core is [Kr] and remaining electrons are filled as $5s^{2}4d^{10}5p^{2}$, so $[Kr]5s^{2}4d^{10}5p^{2}$ is correct.

Answer:

1. C. Br
2. B. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$
3. C. $[Ar]4s^{2}3d^{7}$
4. D. II and III