Formal Charges
Formal charges have an important role in organic chemistry since this concept helps us to know whether an atom in a molecule is neutral/bears a positive or negative charge. Even if some molecules are neutral, the atoms within that molecule need not be neutral atoms.
Polarity Of Water
In simple chemical terms, polarity refers to the separation of charges in a chemical species leading into formation of two polar ends which are positively charged end and negatively charged end. Polarity in any molecule occurs due to the differences in the electronegativities of the bonded atoms. Water, as we all know has two hydrogen atoms bonded to an oxygen atom. As oxygen is more electronegative than hydrogen thus, there exists polarity in the bonds which is why water is known as a polar solvent.
Valence Bond Theory Vbt
Valence bond theory (VBT) in simple terms explains how individual atomic orbitals with an unpaired electron each, come close to each other and overlap to form a molecular orbital giving a covalent bond. It gives a quantum mechanical approach to the formation of covalent bonds with the help of wavefunctions using attractive and repulsive energies when two atoms are brought from infinity to their internuclear distance.
Consider two molecular compounds represented by the Lewis structures shown below.
Substance 1 Substance 2
Which of the following best predicts and explains their relative melting points (mp)?
Ranking Explanation
A) mp(1)>mp(2)
Substance 1 is larger than Substance 2. Its gravitational interactions between molecules are stronger, requiring more energy to break.
B) mp(1)>mp(2)
Substance 1 has more hydrogen bond donor and acceptor sites, so it can engage in a more hydrogen bonds, requiring more energy to break.
C) mp(1)<mp(2)
Substance 1 is more symmetric than Substance 2, so its dipole-dipole forces are weaker, requiring less energy to break.
D) mp(1)<mp(2)
Substance 1 is larger than Substance 2, so it can’t pack as tightly together, resulting in a lower melting point.
E) mp(1)=mp(2)
Substance 1 and Substance 2 are the same molecule, shown in different representations. Therefore, they have the same melting point.
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