Question

When traveling from oxygen to sulfur to selenium, through this group in the periodic table, what is changing?

Answer 1

Horizontal rows are called periods. As you travel downwards, the period is changing. (Oxygen in period 2, sulfur in period 3, and selenium in period 4)

Answer 2

Answer: The size of the element is changing.

Explanation:

Oxygen, sulfur and selenium are the elements which belong to Group 16 and periods 2, 3 and 4 respectively.

Atomic size of an element is defined as the distance between the nucleus and the outermost shell.

In a periodic table, the size of an element decreases as we move across a period and increases as we move down the group.

Down the group, new shell is getting added around the nucleus and electron is getting added in the new shell. Hence, the distance of the outermost shell from nucleus increases.

Therefore, the size of the element is changing.