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.

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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