Covers the geometry of molecules and bond angles, defining valence and dihedral (torsion) angles with examples such as water's H-O-H angle. It then explains bond length and bond energy, the dipole moment with its vector nature and calculation, and the difference between intra- and intermolecular forces. Non-covalent interactions follow, including hydrogen bonds, ionic bonds and the three van der Waals types, ending with their biological role. A closing section adds formal charge, a Pauling electronegativity rule for bond type, and hydrogen bonding anomalies.
Topic 3 of 42 in the MU Sofia syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 11 sections, about 972 words (7 min of reading), with 13 flashcards.
In this note
Basic characteristics of molecules – geometry of the molecules and bond angles :
Chemical Bond length
Chemical Bond energy
Dipole moment
Non-covalent interactions
Van der Waals interactions:
Biological meaning of the non-covalent interactions.
High-Yield Points for the Exam – Characteristics of Molecules
Hydrogen Bonding (Special Case of Intermolecular Forces)
Basic characteristics of molecules – geometry of the molecules and bond angles :
For this sub-point :
Draw the basic types spatial molecular structures
Give Example for each type
Point out the number of Electron bonds
when we mention Bond angels we have to define it and draw examples :
Valence angle : Is the angle formed between two adjacent valent bonds within a molecule. It represents the spatial arrangement of atoms bonded to a central atom. Example : In the water molecule (H-O-H), the valence angle is 104.5º.
Dihedral angle (torsion angle) : The torsion angle defined by four atoms connected by three covalent bonds. The clockwise rotation of the bond in front so as to be superimposed on the bond in back defines a positive torsion angle q. For biological macromolecules, the backbone torsion angles are defined by four contiguous backbone atoms. Torsion angles are preferentially given between -180 and +180°
Chemical Bond length
The chemical bond length: represents the mean distance separating the nuclei of atoms that are covalently bonded, which aligns with the system's lowest energy state. This bond distance is contingent upon the atoms' characteristics, including their hybridization and level of oxidation.
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