a school chemistry project

Periodic Table Trends

A short notebook-style guide to how atoms change across the periodic table. Written by hand, for students.

— by a chemistry student · 2025 —

1. Introduction

The periodic table is more than a grid of letters. If you look carefully, you can see patterns. As you move across a row (left to right) or down a column (top to bottom), the atoms change in size, in how tightly they hold their electrons, and in how strongly they attract new ones.

These patterns are called periodic trends. In this project we will look at three of them: atomic size, ionization energy, and electronegativity.

Simple hand-drawn periodic table grid — fig. 1 — a sketch of the periodic table

2. Explanation of the Trends

2.1 Atomic Size

What it is: the radius of an atom.

The trend: atomic size decreases as you move left to right across a period, and increases as you move down a group.

Why: moving right, more protons pull the electrons closer. Moving down, new electron shells are added, so the atom gets bigger.

Atoms getting smaller across a period — fig. 2 — atoms shrink across a period

2.2 Ionization Energy

What it is: the energy needed to remove one electron from an atom.

The trend: ionization energy increases across a period (left to right) and decreases down a group.

Why: smaller atoms hold their electrons more tightly, so it takes more energy to remove one.

Energy arrows representing ionization energy — fig. 3 — energy needed to remove an electron

2.3 Electronegativity

What it is: how strongly an atom pulls electrons toward itself in a bond.

The trend: electronegativity increases across a period (left to right) and decreases down a group. Fluorine is the most electronegative element.

Why: atoms with nearly-full outer shells really want one more electron.

One atom pulling an electron from another — fig. 4 — one atom pulling an electron from another

Quick summary:

Atomic size → decreases left → right, increases top → bottom.
Ionization energy → increases left → right, decreases top → bottom.
Electronegativity → increases left → right, decreases top → bottom.

3. Short Quiz

Test what you've learned. Choose one answer for each question.

Q1. How does atomic size change as you move left to right across a period?

Q2. Ionization energy is the energy needed to…

Q3. Which element is the most electronegative?

Q4. Atomic size increases as you move…

Q5. Why does ionization energy increase across a period?

Conclusion

Periodic trends help us predict how atoms behave without memorizing every element. Once you understand the patterns, the table starts to make sense.