Atom Examples in Chemistry

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

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

Concept Recap

The smallest unit of an element that retains the chemical properties of that element.

The tiny building blocks everything is made of. Break matter down far enough, you get atoms.

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: Atom starts by naming the element, charge, and relevant protons, neutrons, or electrons.

Common stuck point: Students often know a formula related to atom 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
Describe the basic structure of an atom and identify the three subatomic particles along with their charges.

Answer

Atom=nucleus (protons + neutrons)+electrons\text{Atom} = \text{nucleus (protons + neutrons)} + \text{electrons}

First step

1
An atom consists of a dense central nucleus surrounded by an electron cloud.

Full solution

  1. 2
    The nucleus contains protons (charge +1+1) and neutrons (charge 00).
  2. 3
    Electrons (charge −1-1) orbit the nucleus in energy levels.
Understanding atomic structure is the foundation of all chemistry. Every atom is electrically neutral because the number of protons equals the number of electrons.

Example 2

medium
A carbon atom has 6 protons, 6 neutrons, and 6 electrons. Calculate the approximate mass of this atom in atomic mass units (amu), given that protons and neutrons each have a mass of approximately 11 amu and electrons have negligible mass.

Example 3

medium
An atom loses 2 electrons. State the resulting charge and whether the element identity changes.

Example 4

medium
A neutral atom has mass number 40 and 21 neutrons. Identify the element.

Example 5

hard
Isotope 818O{}^{18}_8\text{O} — state its protons, neutrons, and electrons in the neutral atom.

Example 6

challenge
Two isotopes of magnesium are 24Mg{}^{24}\text{Mg} (78.99%) and 26Mg{}^{26}\text{Mg} (11.01%); the third is 25Mg{}^{25}\text{Mg}. What is the percent abundance of 25Mg{}^{25}\text{Mg}?

Practice Problems

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

Example 1

easy
If an atom has 8 protons, 8 neutrons, and 8 electrons, what element is it and what is its overall charge?

Example 2

easy
If you keep dividing a piece of copper into smaller and smaller pieces, what is the smallest unit that still retains copper's chemical properties?

Example 3

easy
What is the smallest unit of an element that still has that element's chemical properties?

Example 4

easy
A single gold (Au\text{Au}) particle that still behaves chemically like gold is called a what?

Example 5

easy
Are atoms mostly solid matter or mostly empty space?

Example 6

easy
Which three subatomic particles make up an atom?

Example 7

easy
Can a single atom of oxygen be broken into a simpler substance by a chemical reaction?

Example 8

easy
Where in the atom is almost all of its mass concentrated?

Example 9

easy
True or false: atoms can be seen with an ordinary light microscope.

Example 10

easy
How many different kinds of atom does a sample of pure copper contain?

Example 11

medium
An atom has 11 protons, 12 neutrons, and 11 electrons. What is its overall electric charge?

Example 12

medium
A neutral atom has 17 protons. How many electrons does it have, and what element is it?

Example 13

medium
Sodium (Na\text{Na}) and a sodium ion (Na+\text{Na}^+) — which one is a complete neutral atom?

Example 14

medium
Two atoms both have 6 protons but one has 6 neutrons and the other 7. Are they the same element?

Example 15

medium
A helium atom has 2 protons, 2 neutrons, and 2 electrons. What fraction of its particles are in the nucleus?

Example 16

medium
If an atom gains one electron, how does its charge change?

Example 17

medium
An atom has mass number 23 and 11 protons. How many neutrons, and is it the same element as one with 11 protons and 12 neutrons?

Example 18

medium
Why does a chemical reaction never change which element an atom is?

Example 19

medium
A neutral lithium atom has 3 protons and 4 neutrons. State its number of electrons and its overall charge.

Example 20

challenge
An atom of element X has 26 protons and 30 neutrons. A second atom has 26 protons and 28 neutrons. Give the element, and the difference in their mass numbers.

Example 21

challenge
A neutral atom has 19 electrons. After a reaction it has a +1+1 charge. How many protons and how many electrons does it now have, and what element is it?

Example 22

challenge
Atom A: 8 protons, 8 neutrons, 10 electrons. Atom B: 8 protons, 10 neutrons, 8 electrons. Compare their element, charge, and mass number.

Example 23

easy
What is the charge of a proton?

Example 24

easy
What is the charge of a neutron?

Example 25

easy
Which subatomic particle has the smallest mass?

Example 26

easy
An atom of nitrogen has how many protons?

Example 27

easy
True or false: atoms of different elements have different numbers of protons.

Example 28

easy
Are atoms or molecules the basic units of elements?

Example 29

medium
A neutral atom has 14 protons. How many electrons does it have, and what element is it?

Example 30

medium
An atom has mass number 31 and atomic number 15. How many neutrons does it have?

Example 31

medium
An ion with formula Cl−\text{Cl}^- has 17 protons. How many electrons?

Example 32

medium
Why is the mass of an atom essentially the mass of its nucleus?

Example 33

medium
How many electrons does a neutral fluorine atom have?

Example 34

medium
Two atoms have the same atomic number but different mass numbers. What is the term for them?

Example 35

medium
Why is the atom mostly empty space?

Example 36

hard
An ion has charge +3+3 and contains 23 electrons. What is the atomic number of this element?

Example 37

hard
A neutral atom of element X has 16 protons. Predict the most likely ion charge.

Example 38

hard
Why can't a chemical reaction transmute one element into another?

Example 39

hard
An atom's diameter is about 10−10 m10^{-10}\,\text{m} and its nucleus's diameter is about 10−15 m10^{-15}\,\text{m}. By what factor is the atom larger than the nucleus?

Example 40

hard
Atom P has 11 protons and 11 electrons. Atom Q has 11 protons and 10 electrons. Identify which is the atom, which is the ion, and the ion's charge.

Example 41

challenge
Atom W: 11 protons, 11 neutrons, 10 electrons. Atom V: 12 protons, 10 neutrons, 10 electrons. Compare element, charge, and mass number.
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