Overview
This lecture explains three key periodic table trends—atomic radius, ionization energy, and electronegativity—describing their definitions, patterns, and underlying reasons.
Atomic Radius
- Atomic radius is the distance from the nucleus to the outermost electron in an atom.
- Atomic radius increases from top to bottom within a group due to more electron shells.
- Atomic radius decreases from left to right within a period as increased nuclear charge pulls electrons closer.
- Helium has the smallest atomic radius, while francium (or cesium) has the largest.
Ionization Energy
- Ionization energy is the energy required to remove an electron from an atom.
- Higher ionization energy means it is harder to remove an electron.
- Ionization energy increases from left to right within a period, as atoms get smaller and electrons are held more tightly.
- Ionization energy decreases from top to bottom within a group, as atoms get larger and outer electrons are easier to remove.
- Shielding: Inner electrons block the attraction between the nucleus and outer electrons, reducing ionization energy.
Electronegativity
- Electronegativity measures how strongly an atom attracts electrons in a bond, on a scale from 0 (low attraction) to 4 (high attraction).
- Electronegativity increases from left to right within a period and decreases from top to bottom within a group.
- Fluorine has the highest electronegativity (≈4), especially eager to gain electrons to satisfy the octet rule.
- Atoms on the left (e.g., lithium) have low electronegativity and prefer to lose electrons.
Key Terms & Definitions
- Periodic Trend — a predictable pattern in element properties across the periodic table.
- Atomic Radius — the size of an atom, measured from nucleus to outermost electron.
- Ionization Energy — the energy needed to remove an electron from an atom.
- Shielding — the effect of inner electrons reducing the nucleus's pull on outer electrons.
- Electronegativity — an atom’s ability to attract electrons in a bond.
Action Items / Next Steps
- Review the periodic table, focusing on groups and periods for trend patterns.
- Memorize the direction of each trend for atomic radius, ionization energy, and electronegativity.
- Be able to explain the reason behind each trend based on atomic structure.