Question

Choose one of the following terms to match the definition or description given. a. alloy b. specific heat c. crystalline solid d. dipole-dipole attraction e. equilibrium vapor pressure f. intermolecular g. intramolecular h. ionic solids i. London dispersion forces j. molar heat of fusion k. molar heat of vaporization 1\. molecular solids m. normal boiling point n. semiconductor instantaneous dipole forces for nonpolar molecules

Short answer

i. London dispersion forces

Step-by-step solution

Define each term

a. alloy: A mixture of two or more metallic elements. b. specific heat: The heat capacity per unit mass of a substance. c. crystalline solid: A solid in which atoms, ions, or molecules are arranged in a highly ordered, repeating pattern. d. dipole-dipole attraction: Attractive forces between polar molecules with permanent dipoles. e. equilibrium vapor pressure: The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phase. f. intermolecular: Forces occurring between molecules. g. intramolecular: Forces occurring within a molecule. h. ionic solids: Solids composed of positively and negatively charged ions held together by strong electrostatic forces. i. London dispersion forces: Instantaneous dipole-induced dipole forces between nonpolar molecules. j. molar heat of fusion: The amount of heat energy needed to melt one mole of a substance at its melting point. k. molar heat of vaporization: The amount of heat energy needed to vaporize one mole of a liquid at its boiling point. 1. molecular solids: Solids composed of individual molecules held together by intermolecular forces. m. normal boiling point: The temperature at which a liquid boils at 1 atmosphere pressure. n. semiconductor: A substance with electrical conductivity intermediate between that of a conductor and an insulator.

Identify the correct term for the given description

Looking through the list, option i. London dispersion forces is the term that matches the description of "instantaneous dipole forces for nonpolar molecules," since they describe temporary attractive forces resulting from moving electrons in nonpolar molecules. Therefore, the correct answer is: i. London dispersion forces

Key concepts

Understanding London Dispersion Forces

London dispersion forces are a type of intermolecular force, named after the physicist Fritz London, who first described them. These are the weakest type of van der Waals forces and arise due to the temporary fluctuations in electron density within nonpolar molecules.

As electrons move around the nucleus, they can momentarily create an uneven distribution of charge, leading to a temporary dipole. This temporary dipole can induce a dipole in a neighboring molecule. The result is a brief attraction between these two induced dipoles. Although weak and short-lived, when many such interactions occur in a substance, they can significantly affect its physical properties, like boiling and melting points.

London dispersion forces are present in all molecular substances, including noble gases and nonpolar organic compounds. They are particularly important in large, heavy atoms or molecules because the larger electron cloud is more polarizable, enhancing the dispersion forces.

Dipole-Dipole Attraction and Molecular Polarity

In contrast to London dispersion forces, dipole-dipole attractions are intermolecular forces that occur between molecules that have permanent dipole moments. These dipoles arise because of an uneven distribution of electrons across the molecule, often due to electronegative atoms attracting electrons more strongly.

Molecules with polar covalent bonds will interact with each other through dipole-dipole attraction. The positive end of one polar molecule is attracted to the negative end of another, orienting themselves in a way that maximizes this attraction. This force is much stronger than London dispersion forces but weaker than ionic or covalent bonds.

Substances with strong dipole-dipole interactions typically have higher boiling points compared to substances with only London dispersion forces, assuming similar molar masses. The influence of dipole-dipole interaction is evident in the physical properties of polar substances like water.

The Nature of Crystalline Solids

Crystalline solids are materials where atoms, ions, or molecules are arranged in a highly ordered, repeating pattern extending in all three spatial dimensions. This orderly pattern is known as a crystal lattice and can be observed in many everyday materials, from table salt to diamonds.

The repeating units, or unit cells, make up the bulk structure of the crystal. Each unit cell is like a building block containing the exact number of atoms or molecules in a precise arrangement that is replicated throughout the entire structure.

Crystalline solids exhibit flat faces and sharp edges, which are the result of their regular internal structure. These materials often have high melting points and are rigid due to the strong forces, such as ionic or covalent bonds, holding the atoms or molecules in place. The clear-cut structure of crystalline solids contributes heavily to their optical, electrical, and mechanical properties, making them crucial in applications ranging from electronics to jewelry.