Fundamental Principles of Chemical Reactions and Bonding

Chemical Reactions and Fundamental Laws

A chemical reaction is a process by which one or more substances are transformed into one or more different substances. This involves the reorganization of the reactants to form products.

The Law of Conservation of Mass is grounded in the fact that in any chemical reaction, the mass of the reactive substances is equal to the mass of the substances formed.

The Law of Definite Proportions states that when two or more elements combine to form a compound, the ratio between their masses is constant.

Factors Affecting Reaction Speed

The speed of reactions is the variation in the concentration of reactants and products over time. As the reaction progresses, the concentration of the reagents decreases while the products increase. This speed depends on the nature of reactants, surface contact, concentration of reagents, temperature, and catalysts.

Common Types of Chemical Reactions

A neutralization reaction is one in which an acid reacts with a base to form salt and water.

Combustion is a process of rapid oxidation that releases heat and light. Often, the substance that burns is the fuel, and the substance that maintains the combustion is the oxidizer.

Energy and the Activated Complex

An exothermic reaction gives off heat, while an endothermic reaction absorbs heat. The activated complex is an intermediate state between reactants and products in which some links are breaking and others are forming. Activation energy is the energy range from the reactive state to the activated complex.

Properties of Chemical Compounds

Ionic Compounds

Properties of ionic compounds include:

• They are crystalline solids at room temperature with high boiling points.
• They dissolve in water because the lattice is broken and its ions are free.
• When dissolved, they are conductors of electricity and can be attracted to oppositely charged electrodes.
• They are fragile.

Metallic Substances

Properties of metals include:

• They reflect light, giving them a metallic sheen.
• They are good conductors of electricity, ductile, and malleable.
• They are solid at room temperature, except for mercury.
• Alkaline metals have low melting points.
• Hardness varies; while normal metals are very hard, alkaline metals are soft.

Covalent Molecules

Properties of covalent compounds include:

• They have low melting and boiling points because they consist of independent molecules and their intermolecular forces are much weaker.
• They have low densities as independent molecules occupy much volume.
• They do not conduct electricity, or they do so with great difficulty.

Covalency is the number of covalent bonds that an atom can form, which agrees with the number of unpaired electrons in that atom. A polar covalent bond occurs when atoms are joined to another atom with more electrons than the other.

Atomic Structure and Isotopes

A spectrum is a photographic record of the energy that bodies emit. The atomic number is the number of protons in an atom. Two atoms are isotopes if they are part of the same single element, meaning they have the same number of protons but possess different numbers of neutrons; therefore, they have different mass numbers. The mass number is the sum of protons and neutrons.