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Periodic_Table_Trends

Periodic Trends

Overview

  • Fundamental properties that explain changes in behavior and characteristics of elements in the periodic table

Key Concepts

Atomic Radius

  • Definition: Size of an atom or ion.

  • Determining Factors:

    • Number of electron shells

    • Number of protons in the nucleus

  • Trends:

    • Increases down a group of elements due to additional electron shells.

    • Decreases across a period as the number of protons increases, leading to stronger electrostatic attraction pulling electrons closer to the nucleus.

Ionisation Energy (IE)

  • Definition: Energy required to remove an electron from an atom.

  • General Principle: More energy is needed to remove electrons due to the attraction between negatively charged electrons and the positively charged nucleus.

  • Successive Ionisation Energies:

    • Increasing energy is required to remove each successive electron.

    • Significantly more energy is required when removing electrons from electron shells closer to the nucleus.

Electronegativity

  • Definition: Measure of an atom's ability to attract and hold onto electrons.

  • Trends:

    • Increases across a period due to decreasing atomic radius and increasing nuclear charge.

    • Decreases down a group because outer electrons are further from the nucleus and more shielded by inner electrons.

Atomic Radius Trends

Across a Period

  • Number of protons increases, enhancing electrostatic attractions.

  • Outer electrons are in the same shell, leading to atoms becoming smaller.

Down a Group

  • Outermost electrons are in progressively higher shells, moving further from the nucleus.

  • Nuclear charge remains similar, leading to a larger atomic radius.

Example Calculations of Atomic Radius

  1. Comparison of Atomic Radii:

    • Magnesium (Mg): 0.160 nm

    • Aluminium (Al): 0.143 nm

    • Calcium (Ca): 0.197 nm

Reasons for Size Differences:

  • Magnesium vs Aluminium:

    • Same outer electron shell (2,8,2 for Mg and 2,8,3 for Al).

    • Al has +3 nuclear charge (13 protons) compared to Mg's +2 (12 protons), causing electrons to be pulled closer for a smaller radius.

  • Calcium's Size:

    • Ca has outer electrons in fourth shell while Mg has them in third shell, resulting in a larger atomic radius for Ca.

Ionisation Energy Factors

  1. Nuclear Charge: Higher number of protons usually leads to higher ionisation energy.

  2. Atomic Radius: Larger atomic radius can reduce the force of attraction, lowering ionisation energy.

  3. Shielding Effect: More electrons in inner shells can shield the outer electrons from the nucleus, making them easier to remove.

Trends in Ionisation Energy

  • Increases Across a Period: Due to increased nuclear charge and decreasing atomic radius.

  • Decreases Down a Group: Due to increased atomic size and greater shielding effect.

Electronegativity Trends

  1. Increases Across a Period:

    • Atomic radius decreases, resulting in stronger attraction.

  2. Decreases Down a Group:

    • Electrons are further away from the nucleus and more shielded.

Summary of Periodic Trends

  • Atomic Radius: Increases down a group and decreases across a period.

  • Ionisation Energy: Increases across a period and decreases down a group.

  • Electronegativity: Increases across a period and decreases down a group.