Chemistry Concepts: Solutions and Atomic Structure

Solutions and Solubility

Dissolution

Dissolution: Homogeneous is a mixture of two or more substances.

Key Terms

• Solvent: The major component.
• Solute: The minority component.

Solubility Definition

Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a given temperature.

Factors Affecting Solubility

Factors: The solubility depends on the characteristics of the solute and solvent and the temperature of the solution. As a general rule, in the case of the dissolution of a solid into a liquid, the solubility increases as the temperature of the solution increases.

Concentration Measures

Concentration: Indicates the amount of solute dissolved per unit volume of solvent or unit volume of solution:

• Percentage mass concentration (mass percentage)
• Volume concentration
• Molar concentration (Molarity)
• Molal concentration (Molality)
• Molar fraction

Evolution of Atomic Theory

Dalton's Model

Dalton: In his view, matter would be composed of indivisible atoms and thus have no internal structure. However, later discoveries challenged this simple atomic model.

Thomson's Model

Thomson: Key aspects of his atomic model:

1. The atom consists of a mass of positive charge in which subatomic particles—electrons (very small mass and negative electric charge)—are embedded.
2. The number of electrons is sufficient to neutralize the positive charge, so that the atom as a whole is electrically neutral.
3. The electrons of the atom can be separated quite easily.

Rutherford's Model Limitations

Rutherford: Rutherford's model did not explain the stability of the electron orbits in the electron cloud. According to established laws of physics, an electron orbiting the nucleus should emit energy as electromagnetic radiation and therefore should eventually lose energy and collide with the nucleus.

Quantum Theory Introduction

Quantum Theory: Radiant energy is emitted and absorbed discontinuously in packets of energy. These packets were originally called quanta of energy, and later, photons. The German physicist M. Planck (1858–1947) proposed the quantum theory of energy in 1900, stating that every electromagnetic radiation has an associated energy given by the following expression.

Bohr's Model Refinements

Bohr: The electron orbits the nucleus in circular paths, but can only exist in certain allowed orbits with fixed radii and quantized energy values. While in an allowed orbit, the electron neither emits nor absorbs energy. An electron absorbs or emits energy only when it changes its energy level:

• If an electron absorbs a photon of energy, it moves to an excited state and jumps to a higher energy level.
• If an electron loses energy, it drops to a lower level.