Bonding & Structure (Cambridge (CIE) A Level Chemistry): Flashcards
Exam code: 9701
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Define giant ionic lattice.
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Define giant ionic lattice.
A giant ionic lattice is a regular, repeating three-dimensional arrangement of oppositely charged ions held together by electrostatic forces. The type of lattice depends on the relative sizes of the cation and anion.
What are allotropes, and give three examples that are allotropes of carbon?
Allotropes are different structural forms of the same element. Graphite, diamond and buckminsterfullerene (C60) are all allotropes of carbon.
True or False?
Iodine has a giant molecular lattice structure.
False.
Iodine has a simple molecular lattice. Giant molecular lattices are formed by compounds such as diamond, graphite and silicon(IV) oxide.
In a metallic lattice, metal .......... are surrounded by a 'sea' of .......... electrons. The ions are often packed in .......... layers or a cubic arrangement.
In a metallic lattice, metal ions are surrounded by a 'sea' of delocalised electrons. The ions are often packed in hexagonal layers or a cubic arrangement.
Define simple molecular lattice.
A simple molecular lattice is a structure in which small, discrete molecules are arranged in a regular pattern. Intermolecular forces hold the molecules together. Examples include iodine, ice and buckminsterfullerene.
Give three examples of substances with a giant molecular lattice structure.
Silicon(IV) oxide, graphite and diamond all have giant molecular lattice structures, in which atoms are linked throughout by strong covalent bonds.
True or False?
NaCl and MgO both have cubic ionic lattice structures.
True.
Both NaCl and MgO form cubic ionic lattices. The similarity arises because both have a 1:1 ratio of cation to anion.
An ionic bond is the electrostatic force between a positively charged .......... ion and a negatively charged .......... ion. The metal becomes positive by .......... electrons to the non-metal.
An ionic bond is the electrostatic force between a positively charged cation ion and a negatively charged anion ion. The metal becomes positive by transferring electrons to the non-metal.
Why do giant molecular lattices generally have higher melting and boiling points than simple molecular lattices?
Giant molecular lattices require more energy to break because strong covalent bonds (intramolecular forces) extend throughout the whole structure. Simple molecular lattices only require overcoming weaker intermolecular forces between discrete molecules.
Under what conditions can ionic compounds conduct electricity, and why?
Ionic compounds conduct electricity when molten or dissolved in solution. In these states, the ions are free to move and carry charge. In the solid state, ions are in fixed positions and cannot move.
True or False?
Graphite conducts electricity because it has delocalised electrons between its carbon layers.
True.
Graphite has delocalised electrons between its layers that can move when a voltage is applied. Diamond and silicon(IV) oxide do not conduct because all electrons are used in covalent bonds.
Define malleable.
A malleable material can be hammered or shaped without breaking. Metals are malleable because their layers of ions can slide over each other while the delocalised electrons re-form the metallic bonds throughout the new shape.
MgO has a .......... melting point than NaCl because the Mg2+ and O2- ions have a greater .......... than Na+ and Cl- ions, resulting in stronger .......... .
MgO has a higher melting point than NaCl because the Mg2+ and O2- ions have a greater charge density than Na+ and Cl- ions, resulting in stronger electrostatic attraction.
Why do simple covalent substances have low melting and boiling points?
Simple covalent substances have weak intermolecular forces between discrete molecules. Only a small amount of energy is needed to overcome these forces, so they melt and boil at low temperatures.
True or False?
Metals can conduct electricity in both the solid and liquid state.
True.
In both states, metals have mobile delocalised electrons that can move freely and carry charge. This distinguishes metals from ionic compounds, which only conduct when molten or in solution.
Define charge density.
Charge density is the ratio of an ion's charge to its size (ionic radius). Ions with higher charge density exert stronger electrostatic forces, leading to higher melting and boiling points in ionic compounds.
Giant covalent lattices have .......... melting points because a large number of .......... bonds must be broken throughout the structure. Most are .......... in water.
Giant covalent lattices have very high melting points because a large number of covalent bonds must be broken throughout the structure. Most are insoluble in water.
A substance has a high melting point, conducts electricity when solid and is insoluble in water. What type of structure does it have?
It has a giant metallic lattice. Metals conduct in both solid and liquid state (due to mobile delocalised electrons), have high melting points and are insoluble in water.
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