Chemical Bonding tutorial

Describe the structure of calcium.

• metallic lattice structure

• giant metallic lattice structure

• simple metallic lattice structure

Describe the metallic bonding in calcium.

• electrostatic attraction between Ca²⁺ and the sea of electrons

• electrostatic attraction between the Ca and the ‘sea’ of delocalised electrons

• electrostatic attraction between oppositely charged particles

• electrostatic attraction between the Ca²⁺ and the ‘sea’ of delocalised electrons

Which one has greater metallic bond strength, Ca or K? Explain.

• Ca has greater metallic bond strength as there are more delocalised electrons in Ca

• Ca²⁺ has a higher charge density.

• K has greater metallic bond strength as there are more delocalised electrons in K

• K⁺ has a higher charge density.

Answer explanation

Ca has greater metallic bond strength as there are more delocalised electrons in Ca / Ca releases more valence electrons than K. Ca²⁺ has a higher charge and smaller ionic radius than K⁺, thus Ca²⁺ has a higher charge density. As a result there is greater electrostatic attraction between Ca²⁺ and the delocalised electrons in Ca and thus stronger metallic bond strength.

Q. 

Which one has greater metallic bond strength, Li or Na? Explain.

• Na⁺ has a higher charge density.

• Li⁺ has a higher charge density.

• greater electrostatic attraction between Li⁺ and the delocalised electrons

• greater electrostatic attraction between Na⁺ and the delocalised electrons

Which metal has higher electricity conductivity, Ca or K? Explain.

• Ca also has greater electrical conductivity than K as Ca releases more valence electrons, thus there are more mobile charge carriers.

• Ca²⁺  also has greater electrical conductivity than K⁺ as Ca²⁺  releases more valence electrons

• Ca also has greater electrical conductivity than K as Ca releases more valence electrons

• Ca²⁺  also has greater electrical conductivity than K⁺ as Ca²⁺  releases more ions as mobile charge carriers.

Which metal has higher electricity conductivity, Na or Li? Explain.

• Na has higher electrical conductivity as it is smaller.

• Li has higher electrical conductivity as it is smaller.

• Li & Na has the same electrical conductivity as they both release the same amount of valence electrons, so there are the same amounts of mobile charge carriers in both metals.

 

For questions asking about melting point of ionic compound, what should be included in the answer?

• structure

• bonding

• strength of ionic bonds

• number of ionic bonds

Determine which ionic compound has a higher melting point. NaBr and NaF. Give reasons.

Answer explanation

·       NaF has a higher melting point.

·       Both NaF and NaBr have giant ionic structures.

·       The charge and size of cation Na⁺ are the same.

·  The Br ⁻ ion and F⁻ ion have the same charge.

·   The F⁻ ion has a smaller ionic radius than the Br⁻ ion, thus inter-ionic distance between Na⁺ and F⁻ is shorter than that between Na⁺ and Br⁻.

Thus NaF has stronger electrostatic attractions between Na⁺ and F^- ions, requiring more energy to overcome.

Na conducts electricity both in solid and molten state but NaCl conducts electricity only when in the molten state.

 

Explain the observation above in terms of structure and bonding.

Answer explanation

Na has a giant metallic structure with electrostatic attraction between the lattice of Na⁺ and sea of delocalised electrons.  The sea of delocalised electrons which can act as mobile charge carriers, in both solid and molten state.

 

NaCl has a giant ionic structure with electrostatic attraction between oppositely charged ions. In solid state, Na⁺ and Cl⁻ ions are held in fixed positions in the giant ionic lattice. Therefore, there is the absence of mobile charge carriers, hence NaCl does not conduct electricity in the solid state. In the molten state, the ionic lattice is broken down to form mobile ions, which can then act as charge carriers.