📖 Notes LESSON 08 OF 17

Periodic Trends, Locked In

⏱️ 30 min

⚗️ Chemistry

Periodic Trends, Locked In

Atomic structure fundamentals and the periodic trends MDCAT tests most: atomic radius, ionisation energy, and electronegativity across periods and down groups.

Fundamentals

Atomic Structure

➕

Proton

Charge +1, mass ≈1 amu, located in the nucleus. Count of protons = atomic number.

⚪

Neutron

Charge 0, mass ≈1 amu, located in the nucleus alongside protons.

➖

Electron

Charge −1, negligible mass, found in shells around the nucleus.

🔢

Mass Number

Protons + neutrons combined — not the same as atomic number.

Proton: charge +1, located in the nucleus
Neutron: charge 0, located in the nucleus
Electron: charge −1, located in shells
Atomic number = number of protons
Mass number = protons + neutrons

Periodic Trends

Trend Directions

REFERENCE

ACROSS A PERIOD (left → right):
  Atomic radius:      DECREASES
  Ionisation energy:  INCREASES
  Electronegativity:  INCREASES

DOWN A GROUP (top → bottom):
  Atomic radius:       INCREASES
  Ionisation energy:   DECREASES
  Electronegativity:   DECREASES
  Metallic character:  INCREASES

💡

Why these trends happen

Across a period, increasing nuclear charge pulls electrons closer, shrinking atomic radius and making electrons harder to remove. Down a group, extra electron shells and shielding push the outermost electrons further from the nucleus, making them easier to remove.

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