Answer:
… the properties of elements repeat periodically as the atomic number increases.
Explanation:
When you arrange the elements according to their atomic numbers, you find that similar properties recur periodically.
For example, atoms with numbers 3, 11, 19, 37, 55, and 87 are all soft metals that react readily with water.
Elements 4, 12, 20, 38, 56, and 58 are harder metals that react less readily with water , etc.