High School Chemistry  ·  Practice by Skill

Periodic Trends Practice Problems

The periodic table is arranged so that properties repeat in patterns you can predict. Once you know which way each trend runs across a period and down a group, you can compare almost any two elements. Practice below covers table layout, atomic radius, ionization energy, electronegativity, and ion size.

What you’ll practice

  • Table layout: identify groups, periods, and regions such as metals, nonmetals, and metalloids.
  • Atomic radius and ionization energy: predict which way each trend runs across a period and down a group.
  • Electronegativity: compare how strongly atoms pull on shared electrons.
  • Ion formation and size: decide what charge an element forms and whether the ion is bigger or smaller than the atom.

Learn the method first →

A quick example: ranking atomic radius

Rank Mg, Si, and Cl from largest to smallest atomic radius.

All three are in Period 3. Across a period the nuclear charge grows while the electrons stay in the same shell, so the atoms get smaller from left to right.

Left to right is Mg, Si, Cl, so the ranking is Mg > Si > Cl.

3 free periodic trends problems

Give each one a real try before you open the solution. Your answer is checked as soon as you submit it, and the worked solution shows every step so you can see exactly where a setup went wrong.

#1Ion Formation
Bromine (Br) is in Group 17, Period 4. How many electrons does bromine need to gain to achieve a complete outer shell (octet)?
#2Periodic Trends
Atomic radius and first ionization energy move in ______ directions as you travel across a period (left → right) and ______ directions as you travel down a group.
#3Trend Comparison
Compare Be (Period 2, Group 2) and Na (Period 3, Group 1). Which element has the larger atomic radius? Enter the element symbol.

Questions you might have about periodic trends

What is the trend in atomic radius?
Atomic radius decreases from left to right across a period and increases from top to bottom down a group. Moving down adds electron shells, and moving across pulls the same shell in tighter.
What is ionization energy and how does it change?
Ionization energy is the energy needed to remove an electron from a gaseous atom. It generally increases across a period and decreases down a group, so small atoms on the right hold their electrons most tightly.
Why are negative ions larger than their atoms?
Adding an electron increases repulsion among the outer electrons without adding any protons, so the electron cloud spreads out. Positive ions shrink for the opposite reason, and they often lose a whole shell.
What is electronegativity?
Electronegativity measures how strongly an atom attracts the shared electrons in a bond. It rises toward the upper right of the table, which is why fluorine is the most electronegative element.
High School Chemistry · Periodic Trends Practice Problems