extended response practice Flashcards
explain why ionic compounds are brittle?
As a force is applied to the crystal the lattice is disrupted. Ions of the same charge are forced to move next to each other, these repel and the crystal crack. Ionic compounds are brittle
Do I ionic compounds have high or low melting points?
High melting points as the lattice of cations and anions are held with strong electrostatic forces which means when heated it requires a lot of energy to break down.
Are ionic compounds good electrical conductors when solid?
They are poor conductors as the lattice of cations and anions are held in a fixed position which means as these can not move, the solid can not conduct.
Are ionic compounds poor or good electrical conductors when dissolved in water?
Ionic compounds that have been dissolved or that have melted have ions that are free to move around. These ions ‘carry the charge’ through the structure and this allows the compound to conduct electricity.
- Potassium and sodium both react with water, but one metal is so reactive it catches on fire and produces a lilac flame. Explain which metal is more reactive, refer clearly to the electron arrangement of both elements.
Potassium is more reactive than sodium. This is because potassium has 4 shells that contain electrons (K = 2, 8, 8, 1) and sodium only has 3 (2, 8, 1). When they react, each atom loses and electron from the outermost shell. In potassium, the electron is further away from the positive nucleus. It is held less strongly and thus it is easier to remove, so potassium is more reactive.
- Explain why our copper (II) sulfate crystals were brittle.
Ionic substances in solid form are brittle as the anions and cations are held firmly in place. When a force is applied (e.g. bent, hit with a hammer) the positive ions and negative ions can be pushed closer together. As the have the same charge they repel and push the solid apart. Thus it is brittle.
- Explain why iron has a high melting point.
Iron, like all metals, has metallic bonding. Strong electrostatic forces between the cations and delocalised electrons hold the material together. Melting iron requires overcoming these strong forces, which means a lot of heat energy is required.
- Explain why metallic substances are malleable.
Metal cations are able to move around and over each other, held together by the delocalised electrons between the cations to prevent repulsion. As the force is applied the metal, cations can move but electrons also move to keep them together, so the metal can be re-shaped without breaking apart
