Question

unit: electron configurations
\electron configurations for ions\
directions: write the long way and the abbreviated way for all electron configurations.

• atoms that lose electrons are called cations and will have less electrons than protons
• cations have a net positive charge
• atoms that gain electrons are called anions and will have more electrons than protons
• anions have a net negative charge

1. did you read the directions above? ok then, write the electron configuration, for n and n⁻³. how many electrons are in the valence energy level?

n:
n⁻³:
which neutral atom is isoelectronic with n⁻³?
how many valence electrons does neutral n have?

1. write the electron configuration, for cl and cl⁻¹. how many electrons are in the valence energy level?

cl:
cl⁻¹:
which neutral atom is isoelectronic with cl⁻¹?
how many valence electrons does neutral cl have?

1. write the electron configuration, for sr and sr⁺². how many electrons are in the valence energy level?

sr:
sr⁺²:
which neutral atom is isoelectronic with sr⁺²?
how many valence electrons does neutral sr have?

Explanation:

Step1: Find N's electron count

Neutral N has 7 electrons.

Step2: Write N's long config

$1s^2 2s^2 2p^3$

Step3: Write N's abbreviated config

$[He] 2s^2 2p^3$

Step4: Find N⁻³ electron count

N gains 3 electrons: $7+3=10$ electrons.

Step5: Write N⁻³ long config

$1s^2 2s^2 2p^6$

Step6: Write N⁻³ abbreviated config

$[Ne]$

Step7: Identify isoelectronic atom for N⁻³

Ne has 10 electrons, matches N⁻³.

Step8: Count N's valence electrons

Valence shell is n=2: $2+3=5$ electrons.

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Step9: Find Cl's electron count

Neutral Cl has 17 electrons.

Step10: Write Cl's long config

$1s^2 2s^2 2p^6 3s^2 3p^5$

Step11: Write Cl's abbreviated config

$[Ne] 3s^2 3p^5$

Step12: Find Cl⁻¹ electron count

Cl gains 1 electron: $17+1=18$ electrons.

Step13: Write Cl⁻¹ long config

$1s^2 2s^2 2p^6 3s^2 3p^6$

Step14: Write Cl⁻¹ abbreviated config

$[Ar]$

Step15: Identify isoelectronic atom for Cl⁻¹

Ar has 18 electrons, matches Cl⁻¹.

Step16: Count Cl's valence electrons

Valence shell is n=3: $2+5=7$ electrons.

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Step17: Find Sr's electron count

Neutral Sr has 38 electrons.

Step18: Write Sr's long config

$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2$

Step19: Write Sr's abbreviated config

$[Kr] 5s^2$

Step20: Find Sr⁺² electron count

Sr loses 2 electrons: $38-2=36$ electrons.

Step21: Write Sr⁺² long config

$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6$

Step22: Write Sr⁺² abbreviated config

$[Kr]$

Step23: Identify isoelectronic atom for Sr⁺²

Kr has 36 electrons, matches Sr⁺².

Step24: Count Sr's valence electrons

Valence shell is n=5: $2$ electrons.

Answer:

1.
N (long): $1s^2 2s^2 2p^3$; N (abbreviated): $[He] 2s^2 2p^3$
N⁻³ (long): $1s^2 2s^2 2p^6$; N⁻³ (abbreviated): $[Ne]$
Which neutral atom is isoelectronic with N⁻³?: Neon (Ne)
How many valence electrons does neutral N have?: 5

2.
Cl (long): $1s^2 2s^2 2p^6 3s^2 3p^5$; Cl (abbreviated): $[Ne] 3s^2 3p^5$
Cl⁻¹ (long): $1s^2 2s^2 2p^6 3s^2 3p^6$; Cl⁻¹ (abbreviated): $[Ar]$
Which neutral atom is isoelectronic with Cl⁻¹?: Argon (Ar)
How many valence electrons does neutral Cl have?: 7

3.
Sr (long): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2$; Sr (abbreviated): $[Kr] 5s^2$
Sr⁺² (long): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6$; Sr⁺² (abbreviated): $[Kr]$
Which neutral atom is isoelectronic with Sr⁺²?: Krypton (Kr)
How many valence electrons does neutral Sr have?: 2