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MDCAT Worksheet

⚛ Atomic Structure & Periodic Trends

Chapter: Chemistry · Level ★★☆ · Time: 25 min
SCORE___ / 20
NameClassDate
After this worksheet you can
Identify subatomic particlesCalculate atomic/mass numberApply periodic trendsExplain trend causes
📚 Quick Recap

🎯 What you'll practice: Protons/neutrons/electrons, atomic vs mass number, and periodic trends across periods and down groups.

🧠 Section A · Concept Check ● BEGINNER 4 × 1 = 4

1Charge of a proton:
2Atomic number equals the number of:
3Across a period left to right, atomic radius:
4Down a group, ionisation energy:

🧮 Section B · Problem Solving ● INTERMEDIATE 2 + 3×3 = 11

5Mass number = protons + .
6Electronegativity across a period from left to right.
7An atom has 17 protons and 18 neutrons. What is its atomic number and mass number?
8List all four periodic trends going down a group.
9Why does ionisation energy increase across a period?

🚀 Section C · Challenge ● CHALLENGE 5

10Fluorine (Period 2) has a smaller atomic radius than sodium (Period 3, Group 1) even though sodium comes later in the periodic table. Explain this using both trends (across a period and down a group).
💭 Reflection — the most useful thing I learned:
A ___/4   B ___/11   C ___/5   Total ___/20 Teacher's Signature Parent's Signature
✂ answer key — fold or cut before handing out

1-C   2-B   3-B   4-B  |  5 = neutrons   6 = increases   7 = atomic number 17, mass number 35   8 = atomic radius ↑, ionisation energy ↓, electronegativity ↓, metallic character ↑   9 = because nuclear charge increases across a period while shielding stays roughly constant, so the nucleus pulls the outer electrons in more tightly, making them harder to remove  |  10 = Fluorine is far to the right in Period 2, so the across-period trend has shrunk its radius a lot; sodium is in Group 1 of Period 3, one row down, so the down-a-group trend (extra electron shell, more shielding) makes it much larger than fluorine despite fluorine being 'earlier' overall — position in both the period AND the group matters, not just one trend alone.

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