Electron Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Electron.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A negatively charged subatomic particle with negligible mass that occupies energy levels (shells) outside the nucleus.

The particles that do the 'dancing'—they're what's involved in bonding and reactions.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Electron starts by naming the element, charge, and relevant protons, neutrons, or electrons.

Common stuck point: Students often know a formula related to electron but skip the recognition step: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I using particle counts, nuclear charge, mass number, electron arrangement, or isotope notation to describe an atom or ion?

Worked Examples

Example 1

easy
Write the electron configuration for oxygen (Z=8Z = 8).

Answer

1s2 2s2 2p41s^2\,2s^2\,2p^4

First step

1
Oxygen has atomic number 8, so a neutral oxygen atom has 8 electrons. Fill orbitals using the Aufbau principle in order of energy: 1s1s, then 2s2s, then 2p2p.

Full solution

  1. 2
    Fill each subshell to its maximum capacity: 1s21s^2 (2 electrons), 2s22s^2 (2 electrons), leaving 8−4=48 - 4 = 4 electrons for the 2p2p subshell.
  2. 3
    Write the complete electron configuration: 1s2 2s2 2p41s^2\,2s^2\,2p^4. Verify: 2+2+4=82 + 2 + 4 = 8 total electrons.
Electron configurations show how electrons are distributed among energy levels and orbitals. They follow the Aufbau principle, filling lower-energy orbitals first.

Example 2

medium
A chlorine atom (Z=17Z = 17) gains one electron. Write the electron configuration of the resulting Cl−\text{Cl}^- ion and explain why chlorine tends to gain an electron.

Example 3

easy
Write the electron configuration of a neutral lithium atom (Z=3Z=3).

Example 4

medium
Write the electron configuration for O2−\text{O}^{2-} (oxide ion, Z=8Z=8).

Example 5

medium
Explain why a sodium atom forms Na+\text{Na}^+ and not Na−\text{Na}^-.

Example 6

hard
A monatomic ion contains 36 electrons and has charge +2+2. Identify the element and write its noble-gas electron configuration.

Example 7

hard
An atom in the excited state has configuration 1s2 2s2 2p5 3s11s^2\,2s^2\,2p^5\,3s^1. Which neutral element is this, and what is its ground-state configuration?

Example 8

challenge
An electron in a hydrogen atom drops from n=3n=3 to n=2n=2, releasing visible red light. Explain qualitatively why the released photon must have a specific (not arbitrary) energy.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
How many electrons does a neutral atom of magnesium (Z=12Z = 12) have? Write its electron configuration.

Example 2

medium
Which subatomic particle is mainly responsible for chemical bonding, and why?

Example 3

easy
What is the electric charge of a single electron?

Example 4

easy
Where in the atom are electrons found?

Example 5

easy
Which subatomic particle is most responsible for chemical bonding?

Example 6

easy
How does the mass of an electron compare to that of a proton?

Example 7

easy
How many electrons does a neutral atom with 9 protons have?

Example 8

easy
When an atom loses an electron, what is the sign of the resulting ion's charge?

Example 9

easy
Do electrons follow fixed circular orbits like planets around the sun?

Example 10

easy
In a neutral atom, the number of electrons equals the number of which other particle?

Example 11

medium
A neutral sodium atom has 11 electrons. How many electrons does Na+\text{Na}^+ have?

Example 12

medium
How many electrons does a Cl−\text{Cl}^- ion have if chlorine's atomic number is 17?

Example 13

medium
Why does an electron contribute almost nothing to an atom's mass number?

Example 14

medium
A neutral atom has 12 protons. How many electrons does Mg2+\text{Mg}^{2+} have, and what neutral atom has that many electrons?

Example 15

medium
An ion has 18 electrons and a charge of −1-1. How many protons does it have, and what element is it?

Example 16

medium
Why do sodium and potassium behave similarly in reactions when they have different numbers of electrons?

Example 17

medium
An atom gains 2 electrons to become O2−\text{O}^{2-}. If neutral oxygen has 8 electrons, how many does the ion have, and how many protons?

Example 18

medium
How many electrons does a neutral aluminum atom (atomic number 13) have, and how many does Al3+\text{Al}^{3+} have?

Example 19

medium
An atom emits no charge overall and has 5 protons. How many electrons does it have, and what element is it?

Example 20

challenge
A species has 10 electrons. List which neutral atom it could be, plus one cation and one anion that are isoelectronic with it.

Example 21

challenge
An ion of a metal has charge +3+3 and 23 electrons. Identify the proton count, the element, and how many electrons the neutral atom had.

Example 22

challenge
Why is chemistry governed by electrons rather than by protons or neutrons, even though protons define the element?

Example 23

easy
A neutral fluorine atom has 9 protons. How many electrons does it have?

Example 24

easy
Which subatomic particle is found outside the nucleus of an atom?

Example 25

easy
An ion has charge +2+2 and 18 electrons. How many protons does it have?

Example 26

easy
How many electrons fit in the second shell (n=2n = 2) of an atom?

Example 27

medium
How many valence electrons does a neutral phosphorus atom (Z=15Z = 15) have?

Example 28

medium
An atom of silver has 47 protons and 61 neutrons. How many electrons does the neutral atom have, and what is its mass number?

Example 29

medium
Which species has more electrons: S2−\text{S}^{2-} or a neutral argon atom (Z=18Z=18)?

Example 30

medium
A neutral calcium atom forms Ca2+\text{Ca}^{2+}. How many electrons did it lose, and what noble gas does it now resemble in electron count?

Example 31

medium
Light is absorbed by an atom when an electron jumps from a lower to a higher energy level. What happens to the electron's energy?

Example 32

medium
A species has 1818 electrons and charge −2-2. Identify the proton count and the element.

Example 33

medium
How many electrons does a neutral atom of carbon (Z=6Z=6) have in its outer (n=2n=2) shell?

Example 34

hard
Which species in this list is NOT isoelectronic with the others: Na+\text{Na}^+, F−\text{F}^-, Mg2+\text{Mg}^{2+}, Cl−\text{Cl}^-?

Example 35

hard
Two isotopes of chlorine, 35Cl^{35}\text{Cl} and 37Cl^{37}\text{Cl}, are both neutral. How do their electron counts compare, and why does this matter for chemistry?

Example 36

hard
Calcium loses 2 electrons and chlorine gains 1 electron to form CaCl2\text{CaCl}_2. Verify that total electrons are conserved.

Example 37

challenge
A neutral atom X forms a stable ion with charge −3-3 that is isoelectronic with neon. Identify X.
← Back to Electron Practice Mode

Background Knowledge

These ideas may be useful before you work through the harder examples.

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