AP Chemistry Flash Cards – Periodic Trends
Reinforce your understanding of key periodic trends with these AP Chemistry flash cards. Master concepts like effective nuclear charge, atomic and ionic radii, ionization energy, and electron affinity as you get ready for the exam.
Why Periodic Trends Matter
Understanding periodic trends helps you predict and explain the chemical behavior of elements in the periodic table. These trends reflect changes in atomic structure, including nuclear charge, electron shielding, and the number of energy levels.
Flash Cards – Periodic Trend: Atomic Radius
1. Atomic Radius Across a Period (Left to Right)
Atomic radius decreases across a period.
As you move from left to right, each atom gains more protons, increasing the nuclear charge. This stronger pull draws electrons closer to the nucleus. Because electrons enter the same energy level, shielding remains mostly constant. As a result, atoms become smaller across the period.
2. Atomic Radius Down a Group (Top to Bottom)
Atomic radius increases down a group.
Each element adds a new energy shell, which expands the electron cloud. Even though the nuclear charge also increases, the added inner electrons provide more shielding, which reduces the effective pull on the outer electrons. This causes the atoms to grow larger as you move down the group.
2. Periodic Trends-Ionization Energy (IE)
- Increases across a period:
Higher effective nuclear charge (Z_eff) means electrons are held more tightly, requiring more energy to remove the outermost electron. - Decreases down a group:
Outer electrons are farther from the nucleus and more shielded, so they are held less tightly and are easier to remove.
Note: There are exceptions due to subshell stability (e.g., Be vs. B, N vs. O).
3. Periodic Trends-Electron Affinity (EA)
- Generally becomes more negative across a period:
Atoms more readily accept electrons due to increasing Z_eff, releasing more energy when gaining an electron. - Becomes less negative down a group:
Larger atoms have more distance between the nucleus and incoming electron, and increased shielding reduces the attraction, so less energy is released.
4. Periodic Trends-Electronegativity (EN)
- Increases across a period:
Atoms more strongly attract shared electrons in covalent bonds, especially nonmetals like fluorine. - Decreases down a group:
As atomic radius increases, the nucleus is farther from bonding electrons, so the attraction weakens.
Note: Fluorine is the most electronegative element; francium is among the least.
5. Flash cards -Periodic Trends-Effective Nuclear Charge (Z_eff)
- Increases across a period:
More protons in the nucleus, but the same number of inner (shielding) electrons, so outer electrons feel a stronger pull. - Decreases down a group:
While nuclear charge increases, so does the number of inner shells, resulting in similar net attraction felt by valence electrons.
🔸 Flash Cards- Periodic Trends-Application of Trends:
- Predicting chemical reactivity: Metals (low IE and EN) lose electrons easily, nonmetals (high EA and EN) gain electrons easily.
- Explaining bond type and strength: Ionic vs. covalent character depends on EN difference.
- Understanding acid-base behavior: Oxides of elements with high EN (like SO₂) tend to be acidic; those with low EN (like Na₂O) tend to be basic.