hydrogen cyanide, HCN

1.Write the electron-dot structure for the covalent compound hydrogen cyanide, HCN.

Write the electron-dot structure for the covalent compound acetylene, C2H2 3. Examine the three-dimensional geometries of PF5 and SF4 shown below. Which do you think is the more polar compound?

In each molecule, which atom carries the greater positive charge? H¬Cl Br¬F C‚O Br¬Br 5. Which is more polar: a sulfur–bromine (S-Br) bond or a selenium–chlorine (Se-Cl) bond?

The Correct Answer and Explanation is :

1. Electron-dot structure for hydrogen cyanide (HCN):

The structure of HCN involves three atoms: hydrogen (H), carbon (C), and nitrogen (N).

Hydrogen (H) has 1 valence electron, carbon (C) has 4 valence electrons, and nitrogen (N) has 5 valence electrons.
Carbon will be the central atom, and hydrogen and nitrogen will be bonded to it.
Carbon needs 4 electrons to complete its octet, nitrogen needs 3 electrons, and hydrogen needs 2 electrons.
The electron-dot structure is shown as:

H—C≡N

Here, a triple bond is formed between carbon and nitrogen, and a single bond is formed between hydrogen and carbon.

2. Electron-dot structure for acetylene (C2H2):

Acetylene (C2H2) consists of two carbon atoms and two hydrogen atoms. Each carbon atom has 4 valence electrons, and each hydrogen atom has 1 valence electron.

Each carbon atom forms a triple bond with the other carbon atom to complete their octets.
Each carbon also forms a single bond with a hydrogen atom.
The electron-dot structure of acetylene is:

H—C≡C—H

The two carbon atoms are connected by a triple bond, and each carbon is bonded to a hydrogen atom with a single bond.

3. Polar nature of PF5 and SF4:

Examining the three-dimensional structures of PF5 (phosphorus pentafluoride) and SF4 (sulfur tetrafluoride), PF5 has a trigonal bipyramidal geometry, with 5 fluorine atoms surrounding a phosphorus atom. SF4 has a seesaw shape, with 4 fluorine atoms and a lone pair of electrons on the sulfur atom.

PF5: Due to the symmetric geometry, the dipoles cancel each other out, making it a non-polar molecule.
SF4: The lone pair on sulfur causes an asymmetry in the electron distribution, resulting in a polar molecule.

Conclusion: SF4 is more polar than PF5.

4. Greater positive charge in each molecule:

H–Cl: Chlorine is more electronegative than hydrogen, so hydrogen carries the greater positive charge.
Br–F: Fluorine is more electronegative than bromine, so bromine carries the greater positive charge.
C=O: Oxygen is more electronegative than carbon, so carbon carries the greater positive charge.
Br–Br: There is no difference in electronegativity, so neither atom carries a greater positive charge.

5. More polar bond: S-Br vs. Se-Cl:

To determine which bond is more polar, we need to compare the electronegativity values of the atoms involved:

Electronegativity of sulfur (S): 2.58
Electronegativity of selenium (Se): 2.55
Electronegativity of bromine (Br): 2.96
Electronegativity of chlorine (Cl): 3.16

For the S-Br bond:

The difference in electronegativity is |2.96 – 2.58| = 0.38.

For the Se-Cl bond:

The difference in electronegativity is |3.16 – 2.55| = 0.61.

Conclusion: The Se-Cl bond is more polar because the electronegativity difference is greater.

300-word explanation:

Electronegativity is the ability of an atom to attract electrons towards itself in a bond. The larger the difference in electronegativity between two atoms in a bond, the more polar the bond becomes. In the case of the S-Br bond, sulfur (S) and bromine (Br) have an electronegativity difference of 0.38, which means there is a relatively small separation of charge, resulting in a moderately polar bond. On the other hand, the Se-Cl bond has a greater electronegativity difference of 0.61. This larger difference leads to a stronger dipole moment, meaning that the Se-Cl bond is more polar than the S-Br bond.

Polarity also depends on the nature of the atoms involved and their positions in the periodic table. Chlorine and bromine are both halogens, but chlorine is more electronegative than bromine, which contributes to the larger polarity in the Se-Cl bond. Additionally, sulfur and selenium are both in the same group, but sulfur is slightly more electronegative than selenium, further influencing the observed difference in polarity.

Therefore, when comparing the two bonds, the Se-Cl bond is the more polar of the two, due to the larger difference in electronegativity between selenium and chlorine compared to sulfur and bromine. The polarity of bonds influences the physical and chemical properties of the molecules, such as boiling points, solubility, and reactivity.