Mercury electrons

Mercury electrons
1. Mercury-205 has how many protons, neutrons, electrons, and electrons in the 1st quantum shell?

For Mercury-205:
Atomic number (A) = 80
Mass number (Z) = 205

Number of protons = 80 (number of proton is same as the atomic number)
Number of neutrons = 125 (# of neutron = A - Z = 205 - 80 = 125)
Total number of electrons = 80 (same as number of proton for neutral species)

Note: Only electrons occupy quantum shells. Both protons and neutrons are confined in the nucleus.
When only the first quantum shell is considered, mercury has 2 electrons. Because, the 1st quantum shell has only 1 orbital (1s orbital) which can accommodate only 2 electrons.

2. In the compound BCl3 which is the more electronegative element?
Chlorine (Cl) is more electronegative. The trend in the periodic table in terms of electronegativity is increasing from left to right.

3. Which has the higher boiling point?
8-carbon alkane that is a straight chain or an 8-carbon alkane that is branched?

The straight-chain 8-carbon alkane will have the higher boiling point. Compared to branched chain molecule, straight-chain alkane has greater surface area exposed to other molecules, hence, there is stronger intermolecular force of attraction, IMFA, (specifically London dispersion force) that will exist among the molecules. Boiling the substance requires that the IMFA's are broken. Stronger IMFA requires greater energy input, hence higher boiling point for the molecule.
On the other hand, when the molecule becomes branched, it assumes a somewhat spherical conformation resulting in lesser surface area exposed to other molecules, and thus, lesser amount of intermolecular force of attraction can be created among the molecules.

4. Which has the higher octane rating?
An 9=carbon alkane that is a straight chain or an 8-carbon alkane that is branched?

The branched-chain 8-carbon alkane has a higher octane rating than the 9-carbon straight chain alkane. The branched-chain alkane is easier to vaporize because the magnitude of intermolecular forces of attraction among the molecules is lesser due to smaller surface area exposed to other molecules as compared to 9-carbon straight chain alkane. The branched-chain alkane will not form droplets upon entry on the combustion engine that might otherwise impair the uniformity of combustion. The branched-chain alkane is less prone to premature ignition, hence has less tendency to cause "knocking". Therefore, it will have a higher octane rating.

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