1.4 - Ionic Bonding
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What ions is larger, anions (negative) or cations?
• anions
Draw the structure of a NaCl lattice (ionic crystal)
• check in booklet 13 • 6:6 coordination • cubic lattice
Draw the structure of a CsCl ionic crystal
• check booklet 13 • 8:8 coordination • cubic lattice
Explain how ionic bonding occurs
• when a metal and a non metal react together, the metal atom loses electrons and becomes a cation. • the non metal gains electrons and becomes an anion. • there are strong electrostatic forces of attraction between these oppositely charged ions. • this is called ionic bonding.
What is ionic bonding?
• ionic bonding is the result of electrons being transferred completely from one atom to another snd the resulting ions packing together into a crystal lattice
What is a lattice?
• an infinite and repeating arrangement of particles • this structure contributes to the physical properties of ionic compounds
What are the properties of ionic compounds?
• high melting point • high boiling point • good conductors of electricity when molten or in solution
Explain the property of an ionic compound: HIGH MELTING AND BOILING POINT
• strong electrostatic forces between oppositely charged ions • a lot of energy is needed to overcome them • therefore, high melting and boiling point
Explain the property of an ionic compound: GOOD CONDUCTORS OF ELECTRICITY WHEN MOLTEN OR IN SOLUTION
• ionic compounds contain charged ions so they can move towards charged electrodes and will therefore conduct electricity. • in the solid state, ions are not free to move as they are tightly held in place -> they do not conduct electricity • in the liquid/molten state and aqueous state, the ions are mobile and therefore are free to move and carry charge
Why can’t ionic compounds conduct electricity in the solid state?
• in the solid state, ions are not free to move as they are tightly held in place -> they do not conduct electricity • in the liquid/molten state and aqueous state, the ions are mobile and therefore are free to move and carry charge
Describe the trend in cat ionic radius down a group
• cationic radius increases going down a group
Describe similarities and differences between the crystal structures of NaCl and CsCl
• both compounds are ionic and exist in the solid state in a giant ionic crystal lattice • the difference between them lies in the different sizes of the Na and Cs ion • Na+ -> ionic radius 0.095nm • Cs+ -> ionic radius 0.169nm • Cl- -> ionic radius 0.181nm • Cs could accommodate more chloride ions around it than a sodium ion • NaCl = 6:6 coordination • CsCl = 8:8 coordination
What is the coordination number of an ion in a crystal lattice?
• the number of nearest neighbours of opposite charge
Explain why NaCl has a coordination number of 6:6?
• each chloride ions is surrounded by 6 sodium ions as nearest neighbours (oppositely charged ions that are bonded) • each sodium ion is surrounded by 6 chloride ions as nearest neighbours • chloride ion is said to have a coordination number of 6 and the sodium ion is the same • sodium chloride is said to have a 6:6 coordination
How is the sodium chloride lattice described in terms of structure [1]
• cubic
Why is caesium chloride said to have 8:8 coordination?
• each chloride ion is surrounded by 8 caesium ions as nearest neighbours and has a coordination number of 8 • each caesium ion is surrounded by 8 chloride ions as nearest neighbours and has a coordination number of 8 • CsCl has 8:8 coordination
Describe the structure of CsCl
• has a lattice made up of 2 interpenetrating cubic structures
What do the strong electrostatic forces between ions in an ionic lattice account for?
• their high melting points • the hardness of ionic crystals • their low volatility