Periodic Property Sim

Why it matters

Imagine atoms as crowded rooms: adding more floors makes the building taller, but adding more people to one floor forces them to huddle closer.

Predict first

If you move from Lithium to Francium down Group 1, what happens to the atomic radius?

Each step down a group adds a principal energy level (shell), placing valence electrons further from the nucleus despite the increased nuclear charge.

• It decreases because the nucleus gets heavier
• It increases because new electron shells are added — correct
• It stays the same because protons increase too

What you do

Build potassium — 19 protons, 20 neutrons and 19 electrons (mass number 39): the shells fill 2, 8, 8, 1. That is one more occupied floor than sodium — a bigger atom whose lone outer electron sits farther from the nucleus, easier to lose.

Check yourself

Why does atomic size decrease from Sodium (Na) to Chlorine (Cl) across Period 3?

Across a period, electrons enter the same shell while protons increase. The stronger effective nuclear charge pulls the electron cloud inward.

Which atom is the largest?

Cesium (Cs) is near the bottom-left of the periodic table and, among these options, has the most electron shells and a low effective nuclear charge on its valence electron, making it the largest.

• Electrons are removed from the outer shell
• Increased nuclear charge pulls the same shell closer — correct
• The number of shells decreases
• Protons repel electrons outward
• Fluorine (F)
• Cesium (Cs) — correct
• Oxygen (O)
• Neon (Ne)