What is the trend in atomic radius across Period 3 of the Periodic Table?

In Period 3, the atomic radius decreases from left to right across the period. This is because as you move across the period, the number of protons in the nucleus increases, leading to a greater nuclear charge. This increased attraction pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.

How does the electronegativity change across Period 3 elements?

Electronegativity increases across Period 3 from left to right. This is due to the increasing nuclear charge, which attracts the bonding pair of electrons more strongly. Elements like sodium have lower electronegativity, while chlorine has a higher electronegativity, reflecting its strong ability to attract electrons.

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

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, which is strong and leads to higher melting and boiling points. Silicon, a metalloid, has a giant covalent structure, resulting in very high melting and boiling points. Non-metals like phosphorus, sulfur, and chlorine have molecular structures with weaker van der Waals forces, leading to lower melting and boiling points.

What is the trend in ionization energy across Period 3?

Ionization energy generally increases across Period 3. This is because the increasing nuclear charge across the period results in a stronger attraction between the nucleus and the outer electrons, making it more difficult to remove an electron. However, there are slight deviations due to electron configurations, such as the drop between magnesium and aluminum, and phosphorus and sulfur.

How do the chemical properties of Period 3 elements change across the period?

The chemical properties of Period 3 elements change from metallic to non-metallic as you move from left to right. Metals like sodium and magnesium react by losing electrons, while non-metals like chlorine gain electrons during reactions. This change is due to the increasing electronegativity and ionization energy across the period, which influences how these elements interact with other substances.

The Periodic Table: chemical periodicity(AS-Level Inorganic Chemistry)Cambridge International A Levels Chemistry (9701)

Periodicity of chemical properties of the elements in Period 3

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Study Notes

Period 3 elements show a variety of chemical properties due to differences in their reactions with oxygen, chlorine, and water, as well as their oxidation numbers and bonding characteristics.

Reaction with Oxygen — Elements react with oxygen to form oxides, which can be basic, acidic, or amphoteric. Example: Sodium reacts with oxygen to form sodium oxide, a basic oxide.
Reaction with Chlorine — Elements form chlorides, which can be ionic or covalent. Example: Sodium reacts with chlorine to form sodium chloride, an ionic compound.
Oxidation Number — Indicates the charge an atom would have if all bonds were ionic. Example: In Na2O, sodium has an oxidation number of +1.
Electronegativity — A measure of an atom's ability to attract electrons in a bond. Example: Electronegativity increases across Period 3, affecting bonding type.
Chemical Bonding — Elements form ionic or covalent bonds based on electronegativity differences. Example: NaCl is ionic, while PCl5 is covalent.

Exam Tips

Key Definitions to Remember

Reaction with Oxygen
Reaction with Chlorine
Oxidation Number
Electronegativity
Chemical Bonding

Common Confusions

Confusing ionic and covalent bonding
Misunderstanding the role of electronegativity in bonding

Typical Exam Questions

What happens when sodium reacts with oxygen? Sodium forms sodium oxide, a basic oxide.
How does magnesium react with chlorine? Magnesium forms magnesium chloride, an ionic compound.
What is the oxidation number of sulfur in SO3? The oxidation number of sulfur in SO3 is +6.

What Examiners Usually Test

Understanding of reactions of Period 3 elements with oxygen and chlorine
Ability to determine oxidation numbers
Knowledge of trends in electronegativity and their effects on bonding

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