Element Examples in Chemistry

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

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 pure substance consisting entirely of atoms with the same number of protons (same atomic number), which cannot be broken down into simpler substances by any chemical reaction. There are 118 known elements, organized in the periodic table.

A pure substance that can't be broken down chemically. Gold is gold, oxygen is oxygen.

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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: The atomic number (number of protons) uniquely defines the element — change it, and you have a new element.

Common stuck point: An element is defined by protons, not electrons or neutrons.

Sense of Study hint: When identifying an element, look at its atomic number (proton count). First find the element on the periodic table by atomic number or symbol. Then note that changing protons changes the element entirely, while changing neutrons only creates an isotope. Finally, remember that elements can exist as single atoms (He), diatomic molecules (\text{O}_2), or larger structures (\text{S}_8).

Worked Examples

Example 1

easy
Explain why gold (Au) and oxygen (O) are considered elements, while water (\text{H}_2\text{O}) is not.

Solution

  1. 1
    An element is a pure substance made of only one type of atom.
  2. 2
    Gold contains only gold atoms and oxygen contains only oxygen atoms, so both are elements.
  3. 3
    Water contains two different types of atoms (hydrogen and oxygen) chemically bonded, making it a compound, not an element.

Answer

\text{Elements contain only one type of atom; compounds contain two or more.}
Elements are the simplest pure substances and cannot be broken down into simpler substances by chemical means. There are currently 118 known elements organized in the periodic table.

Example 2

medium
Iron (Fe) has atomic number 26. How many protons and electrons does a neutral iron atom have? If iron forms the \text{Fe}^{3+} ion, how many electrons does it have?

Practice Problems

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

Example 1

easy
Classify each as an element or compound: (a) \text{Na}, (b) \text{CO}_2, (c) \text{Ne}, (d) \text{NaCl}.

Example 2

medium
Sample A has atoms with 8 protons and 8 electrons. Sample B has atoms with 8 protons and 10 electrons. Are they the same element? Explain.
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Background Knowledge

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

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