For which compounds containing a heteroatom (an atom other than carbon or hydrogen) does the molecular ion have an even-numbered mass and for which does it have an odd-numbered mass? (a) A chloroalkane with the molecular formula \(\mathrm{C}_{n} \mathrm{H}_{2 n+1} \mathrm{Cl}\). (b) A bromoalkane with the molecular formula \(\mathrm{C}_{n} \mathrm{H}_{2 n+1} \mathrm{Br}\). (c) An alcohol with the molecular formula \(\mathrm{C}_{n} \mathrm{H}_{2 n+1} \mathrm{OH}\). (d) A primary amine with the molecular formula \(\mathrm{C}_{n} \mathrm{H}_{2 n-1} \mathrm{NH}_{2}\). (e) A thiol with the molecular formula \(\mathrm{C}_{n} \mathrm{H}_{2 n+1} \mathrm{SH}\).

To calculate the molecular mass of each compound, we first need to know the atomic masses of the involved atoms. Here they are (rounded to the nearest whole number for simplicity): - Carbon (C): 12 - Hydrogen (H): 1 - Chlorine (Cl): 35 - Bromine (Br): 80 - Oxygen (O): 16 - Nitrogen (N): 14 - Sulfur (S): 32

We are given a chloroalkane with the molecular formula \(\mathrm{C}_{n} \mathrm{H}_{2n+1} \mathrm{Cl}\). The molecular mass for this compound can be calculated by plugging in the atomic masses of C, H, and Cl: Molecular mass = (12n) + (1 * (2n + 1)) + 35

Since 12n and 35 are both odd terms, the molecular mass of a chloroalkane is odd if (2n + 1) is odd. As n increases, (2n + 1) will always remain odd, so the molecular mass of a chloroalkane is odd.

Proceed similarly for the other compounds: (a) Bromoalkane: Molecular mass = (12n) + (1*(2n + 1)) + 80 => The molecular mass is even since all terms are even. (b) Alcohol: Molecular mass = (12n) + (1 * (2n + 1)) + 16 + 1 => The molecular mass is odd since 12n is an even term and (2n + 1) + 16 + 1 is an odd term. (c) Primary amine: Molecular mass = (12n) + (1 * (2n - 1)) + 14 + 2 => The molecular mass is even since all terms are even. (d) Thiol: Molecular mass = (12n) + (1 * (2n + 1)) + 32 + 1 => The molecular mass is odd since 12n is an even term and (2n + 1) + 32 + 1 is an odd term. In summary: (a) Chloroalkane (CnH(2n+1)Cl) - odd-numbered mass (b) Bromoalkane (CnH(2n+1)Br) - even-numbered mass (c) Alcohol (CnH(2n+1)OH) - odd-numbered mass (d) Primary amine (CnH(2n-1)NH2) - even-numbered mass (e) Thiol (CnH(2n+1)SH) - odd-numbered mass