Question 1

What is meant by the periodicity of physical properties in Period 3 elements?

Accepted Answer

Periodicity of physical properties refers to the recurring trends observed in the physical characteristics of elements as you move across Period 3 of the Periodic Table. These properties include atomic radius, ionization energy, electronegativity, and melting and boiling points. Understanding these trends is crucial for Cambridge International A Levels Chemistry students as it helps predict the behavior of elements based on their position in the Periodic Table.

Question 2

How does atomic radius change across Period 3 and why?

Accepted Answer

As you move across Period 3 from sodium to argon, the atomic radius decreases. This is because the number of protons in the nucleus increases, resulting in a stronger positive charge that pulls the electron cloud closer to the nucleus. Despite the addition of more electrons, they are added to the same energy level, so the increased nuclear charge outweighs the electron-electron repulsion, leading to a smaller atomic radius.

Question 3

Why do melting and boiling points vary across Period 3 elements?

Accepted Answer

The melting and boiling points of Period 3 elements vary due to differences in their structures and bonding. Metals like sodium, magnesium, and aluminum have metallic bonding, with melting and boiling points increasing from sodium to aluminum due to stronger metallic bonds. Silicon, a metalloid, has a giant covalent structure, resulting in very high melting and boiling points. Non-metals like phosphorus, sulfur, chlorine, and argon have molecular structures with weaker van der Waals forces, leading to lower melting and boiling points.

Question 4

What trend is observed in ionization energy across Period 3?

Accepted Answer

Ionization energy generally increases across Period 3 from sodium to argon. This is because the nuclear charge increases, making it more difficult to remove an electron. However, there are slight deviations at aluminum and sulfur due to electron configurations. For instance, aluminum has a lower ionization energy than magnesium because its outer electron is in a higher energy p-orbital, and sulfur has a lower ionization energy than phosphorus due to electron-electron repulsion in its p-orbitals.

Question 5

How does electronegativity change across Period 3 and what is its significance?

Accepted Answer

Electronegativity increases across Period 3 from sodium to chlorine. This is because the increasing nuclear charge attracts the bonding pair of electrons more strongly. Electronegativity is significant as it influences the type of bonding and reactivity of elements. For example, elements with higher electronegativity, like chlorine, tend to form covalent bonds, while those with lower electronegativity, like sodium, are more likely to form ionic bonds. Understanding these trends is essential for Cambridge International A Levels students studying chemical periodicity.

Periodicity of physical properties of the elements in Period 3

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