Practice Element in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

Quick 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.

Example 1

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

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?

Example 3

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

Example 4

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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