Electron Configuration

Sublevel Basics

100

How many electrons can an s sublevel hold?

2 (the s sublevel has only one orbital, and each oribtal holds 2 electrons)

200

How many electrons can a p sublevel hold? 

6 (The p sublevel has 3 orbitals, each holding 2 electrons, so 3x2 is 6)

300

How many electrons can a d sublevel hold?

10 (the d sublevel has 4 orbitals, each holding 2 electrons.)

400

Which sublevel comes after 3p in energy filling?

4s (After 3p, the next lowest energy orbital is 4s according to the filling order)

500

Which sublevel comes first after 4s in energy filling?

3d (After 4s is filled, electrons start filling the 3d orbitals)

Electron Counts

100

How many orbitals can the 1st energy level hold?

2 (the first energy level has only an s orbital)

200

How many electrons can the 2rd energy level hold?

8 (2s (2) + 2p (6) = 8)

300

How many electrons are in the 3s and 3p combined? 

8 (3s holds 2 electrons, 3p hold 6, total = 8)

400

How many electrons can the 3rd energy level hold with s, p and d? 

18 (3s (2) + 3p (6) + 3d (10) = 18 electrons)

500

Total electrons that completely fill the 4th energy level (s, p, d only)

18 (4s (2) + 4p (6) +3d (10) = 18)

Full Configurations

100

Give the Full Electron Configuration for Hydrogen(H)

1s¹ (Hydrogen has 1 electron, so it fills the first s orbital)

200

Give the Full Electron Configuration for Oxygen (O)

1s²2s²2p⁴ (After filling 1s and 2s, the 4 remaining electrons go into 2p)

300

Give the Full Electron Configuration for Magnesium (Mg)

1s²2s²2p⁶3s² (After the first 10 electrons, the last 2 go into 3s)

400

Give the Full Electron Configuration for Sulfur (S)

1s²2s²2p⁶3s²3p⁴ (After 3s is filled, 4 electrons go into 3p)

500

Give the Full Electron Configuration for Iron (Fe)

1s²2s²2p⁶3s²3p⁶4s²3d⁶ (After 4s², 6 electrons go into 3d)

Noble Gas Shorthands

100

Give the Noble Gas Shorthand for Neon (Ne)

[He] 2s²2p⁶ ([He] represents 1s², the remaining 8 electrons fill 2s²and 2p⁶)

200

Give the Noble Gas Shorthand for Sodium (Na)

[Ne] 3s1

300

Give the Noble Gas Shorthand for Vanadium (V)

[Ar] 4s² 3d³ (After Argon’s 18 electrons, 5 electrons fill 4s² then 3d³)

400

Give the Noble Gas Shorthand for Iridium (Ir)

[Xe] 4f¹⁴ 5d⁷ 6s² (Ir has 77 electrons. After Xenon, 14 fill 4f, 7 fill 5d, and 2 fill 6s)

500

Give the Noble Gas Shorthand for Livermorium (Lv)

[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁴(After Radon (86 e⁻), 14 electrons fill 5f, 10 fill 6d, 2 fill 7s, and 4 go into 7).

Exceptions and Tricks (Hard)

100

Why does Chromium (Cr) have the configuration [Ar] 4s¹ 3d⁵ instead of [Ar] 4s² 3d⁴?

Chromium shifts one electron from 4s to 3d because a half-filled d⁵ sublevel is more stable than d⁴. This makes 4s¹ 3d⁵ lower in energy.

200

Copper (Cu) does not follow the normal filling pattern. What is its correct shorthand configuration and why?

[Ar] 4s¹ 3d¹⁰ (Copper steals an electron from 4s so 3d can become fully filled (d¹⁰), which is extremely stable.)

300

One of these is wrong. Which one, and why?

A. Mo → [Kr] 5s¹ 4d⁵

B. Zn → [Ar] 4s² 3d¹⁰

C. Ag → [Kr] 5s² 4d⁹

C is incorrect. Ag is an exception like Cu:Ag → [Kr] 5s¹ 4d¹⁰ It shifts an electron from 5s → 4d to complete d¹⁰.

400

Why do some elements switch to an s¹ ending instead of s², even though most elements end with s²?

Some atoms gain extra stability when their d-subshell becomes half-full (d⁵) or completely full (d¹⁰). To get that stability, they move one electron from the s sublevel into the d sublevel.

500

Which element has this configuration, and why is it special? [Kr] 5s¹ 4d¹⁰

Silver (Ag) (It should be 5s² 4d⁹, but it shifts to 5s¹ 4d¹⁰ to make the d-subshell completely full.)