(b) How would you expect the H¬X¬H bond angle to vary in the series H2O, H2S, H2Se? Explain. (Hint: The size of an electron pair domain depends in part on the electronegativity of the central atom.)

Verified step by step guidance

1. insert step 1> Consider the molecular geometry of each compound: H2O, H2S, and H2Se. All these molecules have a bent shape due to the presence of two lone pairs on the central atom, which is typical for molecules with the formula H2X where X is a group 16 element.
2. insert step 2> Understand that the bond angle is influenced by the repulsion between electron pairs. According to VSEPR theory, lone pairs repel more strongly than bonding pairs, which affects the bond angle.
3. insert step 3> Consider the electronegativity of the central atom. Oxygen is more electronegative than sulfur and selenium. Higher electronegativity means the lone pairs are held closer to the central atom, increasing their repulsion with bonding pairs.
4. insert step 4> As you move down the group from oxygen to selenium, the central atom becomes less electronegative, and the size of the atom increases. This results in the lone pairs being further from the central atom, reducing their repulsion with bonding pairs.
5. insert step 5> Predict that the H-X-H bond angle will decrease from H2O to H2S to H2Se due to the decreasing electronegativity and increasing atomic size, which reduces the repulsion between the lone pairs and bonding pairs.

Key Concepts

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory is a model used to predict the geometry of molecular structures based on the repulsion between electron pairs surrounding a central atom. According to this theory, electron pairs, including bonding and lone pairs, will arrange themselves to minimize repulsion, which directly influences bond angles. In the case of H2O, H2S, and H2Se, the presence of lone pairs and the size of the central atom will affect the bond angles.

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons within a chemical bond. In the context of H2O, H2S, and H2Se, the electronegativity of the central atom (O, S, Se) influences the distribution of electron density and the size of the electron pair domains. Higher electronegativity leads to stronger attraction of bonding electrons, which can affect the bond angles due to changes in electron pair repulsion.

Bond Angles and Atomic Size

Bond angles are the angles formed between adjacent bonds in a molecule and are influenced by the size of the central atom. As the central atom increases in size from oxygen to sulfur to selenium, the bond angles tend to decrease due to the larger electron pair domains that result from the increased distance between the nuclei. This trend is important for understanding how the geometry of H2O, H2S, and H2Se varies.