4.2 AS Level

Bonding and structure

10 flashcards to master this topic

Key Concept Flip

Describe the lattice structure of sodium chloride (NaCl).

Answer Flip

Sodium chloride has a giant ionic lattice structure. It consists of alternating Na+ and Cl- ions held together by strong electrostatic forces in a three-dimensional arrangement.

Key Concept Flip

How does the type of bonding and structure affect the melting point of a substance?

Answer Flip

Stronger bonding (

Example: giant ionic, giant metallic, giant covalent) generally leads to higher melting points due to the greater energy required to overcome the strong attractive forces. Simple molecular substances have weak intermolecular forces and thus lower melting points.
Definition Flip

Define standard enthalpy change of formation (ΔHf⦵).

Answer Flip

The standard enthalpy change of formation is the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions (298 K and 101 kPa).

Example: ΔHf⦵ [H₂O(l)] is the enthalpy change for H₂(g) + 1/2 O₂(g) → H₂O(l).
Key Concept Flip

Explain, in terms of bond breaking and bond making, why a reaction is exothermic.

Answer Flip

A reaction is exothermic when the energy released from forming new bonds in the products is greater than the energy required to break the bonds in the reactants. This results in a net release of energy as heat. Therefore, ΔH is negative.

Key Concept Flip

What does a reaction pathway diagram show, and what information can be obtained from it?

Answer Flip

A reaction pathway diagram illustrates the energy changes that occur during a chemical reaction. It shows the enthalpy change of the reaction (ΔH) and the activation energy (Ea), which is the energy required to initiate the reaction.

Definition Flip

Define Hess's Law.

Answer Flip

Hess's Law states that the total enthalpy change for a reaction is independent of the pathway taken, provided the initial and final conditions are the same. This allows for calculation of enthalpy changes that cannot be directly measured.

Key Concept Flip

How do you determine the oxidation number of an atom in a compound?

Answer Flip

Apply oxidation number rules: Free elements have ON of 0, oxygen is usually -2, hydrogen is usually +1. The sum of ONs in a neutral compound is 0; in an ion, it equals the ion's charge.

Example: in H₂SO₄, the ON of S is +6.
Definition Flip

Explain the terms 'oxidation' and 'reduction' in terms of electron transfer.

Answer Flip

Oxidation is the loss of electrons (OIL - Oxidation Is Loss), resulting in an increase in oxidation number. Reduction is the gain of electrons (RIG - Reduction Is Gain), resulting in a decrease in oxidation number.

Example: Zn → Zn²⁺ + 2e⁻ (oxidation).
Definition Flip

State Le Chatelier's principle.

Answer Flip

Le Chatelier's principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. These 'changes' include changes in temperature, pressure, or concentration.

Key Concept Flip

Write the Kc expression for the following equilibrium: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Answer Flip

Kc = [NH₃]² / ([N₂] [H₂]³). The equilibrium constant Kc is the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to the power of its stoichiometric coefficient.

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3.7 Dot-and-cross diagrams 8.1 Rate of reaction