25.) Explain the following:
(a)Water exists as liquid while H2S exist as a gas
(b)HF has higher boiling point than HCl
(c)Ice has less density than water
(d)Metals have bright luster
(a) Water exists as a liquid while H2S exists as a gas because of the differences in intermolecular forces and molecular structure. Water molecules are polar, meaning they have a slight positive charge on one end and a slight negative charge on the other. This polarity allows water molecules to form hydrogen bonds with each other, resulting in a relatively strong attractive force between the molecules. These hydrogen bonds make it more difficult for water molecules to break apart and turn into a gas. On the other hand, H2S molecules are nonpolar and do not have the ability to form hydrogen bonds. As a result, the intermolecular forces between H2S molecules are weaker, leading to a lower boiling point compared to water.
To understand this, one can look at the molecular structures of water and H2S, as well as their polarity. Water (H2O) has two hydrogen atoms bonded to an oxygen atom in a bent shape, creating a polar molecule. H2S, on the other hand, has two hydrogen atoms bonded to a sulfur atom in a linear shape, resulting in a nonpolar molecule.
(b) HF (hydrofluoric acid) has a higher boiling point than HCl (hydrochloric acid) because of the differences in polarity and intermolecular forces between the molecules. HF is a polar molecule due to the electronegativity difference between hydrogen and fluorine, resulting in a partial positive charge on hydrogen and a partial negative charge on fluorine. This polarity allows HF molecules to form stronger hydrogen bonds compared to HCl, which is not as polar and has weaker intermolecular forces.
To understand this, one can compare the electronegativity difference between the atoms involved in the bonds. In the case of HF, fluorine is highly electronegative, which results in a larger difference in electronegativity between hydrogen and fluorine. This larger difference creates a stronger partial positive charge on hydrogen and a stronger partial negative charge on fluorine, leading to stronger hydrogen bonds between the HF molecules.
(c) Ice has less density than water because of the unique structure of ice crystals. Normally, when a substance solidifies, its molecules arrange themselves in a way that is more closely packed, leading to an increase in density. However, water is an exception to this behavior due to hydrogen bonding.
When water freezes, its molecules form a hexagonal lattice structure, where each water molecule is hydrogen-bonded to four neighboring water molecules. This structure creates open spaces or "holes" within the lattice, resulting in a lower density compared to liquid water.
To understand this, one can visualize the arrangement of water molecules in the solid and liquid states. In the liquid state, the water molecules are in constant motion and are less ordered. In the solid state, the water molecules form a more organized arrangement with hydrogen bonds, resulting in a less dense structure.
(d) Metals have a bright luster because of their unique properties of conductivity and reflectivity. Metals have a high density of free electrons within their atomic structure, which allows them to conduct electricity and heat efficiently.
When light waves interact with the free electrons in metals, the electrons absorb and then re-emit the light, causing the metal to reflect light waves. This reflection of light gives metals their characteristic shine or luster.
To understand this, one can imagine light waves interacting with the free electrons within a metal. Instead of being absorbed or scattered like in non-metallic materials, the light waves are reflected by the free electrons, resulting in a bright and shiny appearance.