Achiever's Dream Chemical Bonding Pt 1 Notes

The Chemistry Specialist Chemical Bonding Part 1

CHEMICAL BONDING Melting/boiling point comparisons All questions regarding prediction of melting/boiling points can be broadly classified into 2 categories: The following template can be used to answer most questions regarding prediction of melting/boiling point of different compounds with similar molecular mass. It fails when different molecular masses are being compared, for example SO 2 vs SO3, resulting in the predominant bonding being id-id instead of pd-d as expected. 1. Comparing A vs B of different structures it can be further subdivided into Comparison between different structures Comparison between same structures Structures with different types of bonding Structure Structure Bonding Energy Structures with same types of bonding FORMAT Structure + Bonding A has Structure of A with Bonding of A B has Structure of B with Bonding of B Energy Since Bonding of A is stronger than the Bonding of B, more energy is required to overcome this stronger force of A B. 2. Comparing A vs B with same structures Structure Both A and B have Structure of A & B Different Bonding Bonding A has Bonding of A B has Bonding of B Both A & B have Bonding of A and B Bonding Energy Energy Same Bonding Since Bonding of A is stronger than the Bonding of B, more energy is required to overcome this stronger force of attraction. Hence, A has higher melting/boiling point than B. Since A has Factors affecting bond compared to B, it has stronger Bonding of A and B which requires more energy to overcome. Hence, A has higher melting/boiling point than B. © Achievers Dream

Different Structures Mg has a giant metallic lattice structure with strong electrostatic forces of attraction between the cations and sea of delocalised mobile electrons . CCl₄ is non-polar and has a simple molecular structure with weak instantaneous dipole – induced dipole forces of attraction between its molecules. Since the strong electrostatic forces of attraction between the cations and sea of delocalised mobile electrons in Mg is stronger than the weak instantaneous dipole – induced dipole forces of attraction in CC l 4, more energy is required to overcome Hence, Mg point than CCl . © Achievers Dream Same Structures Different Bonding Same Structures Same Bonding Same Structures Same Bonding Mg vs CCl4 (giant metallic vs simple molecular) Cl2 vs NH3 (simple molecular) NaCl vs MgCl2 (giant ionic) Structure + Bonding Energy Both Cl2 and NH3 have a simple molecular structure . Since hydrogen bonding in NH 3 is stronger than the instantaneous dipole – induced dipole forces of attraction in Cl 2, more energy is required to overcome this stronger NH3 has Cl2. Structure Cl2 is non polar and has weak instantaneous dipole – induced dipole forces of attraction between its molecules. NH3 is polar and has strong hydrogen bonding between its molecules. Bonding Energy Both NaCl and MgCl2 have a giant ionic lattice structure. Since both compounds has the same anion but the charge of Mg 2+ is larger than that of Na + and the ionic radius of Mg 2+ is smaller than that of Na +, MgCl2 has a larger lattice energy and has stronger ionic bond which requires more energy to overcome. Hence, MgCl2 has higher melting/boil- ing point than NaCl. requires more energy to overcome. Hence, H 2O has higher melting/boiling point than HF. Structure Both NaCl and MgCl2 have strong electrostatic forces of attraction between their 2 oppositely charged ions. Bonding Energy H2O vs HF (simple molecular) Both H2O and HF have a simple molecular structure. Since H2O has on AVERAGE 2 hydrogen bonds per molecule while HF has on AVERAGE 1 hydrogen bond per molecule, H 2O has more extensive hydrogen bonds which Structure Both H2O and HF are polar and have hydrogen bonding between its molecules . Bonding Energy