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.