Atomic Structure & Bonding

Ionic vs. Covalent Bonding

Atoms form chemical bonds to achieve greater stability, typically by attaining a full outer electron shell. The two primary types of chemical bonds are ionic and covalent bonds, which differ in how electrons are distributed between atoms.

• Ionic Bonds: Formed when one atom transfers electrons to another, resulting in the formation of oppositely charged ions. This usually occurs between a metal (which loses electrons) and a non-metal (which gains electrons). The resulting electrostatic attraction holds the ions together.

• Covalent Bonds: Formed when two atoms share one or more pairs of electrons. This typically occurs between non-metal atoms, allowing both to achieve a stable electron configuration.

• Example: Sodium chloride (NaCl) is an example of an ionic compound, while water (H2O) is an example of a covalent compound.

Atomic Properties

Atomic Number and Mass Number

Each element is defined by its atomic number, which is the number of protons in its nucleus. The mass number is the sum of protons and neutrons.

• Atomic Number (Z): Number of protons in the nucleus. For sodium, Z = 11.

• Mass Number (A): Total number of protons and neutrons. For sodium with 11 protons and 12 neutrons, A = 23.

• Example: Sodium (Na) has 11 protons and 12 neutrons, so its mass number is 23.

Periodic Properties

Stability of Noble Gases

Noble gases (Group 18 elements) are characterized by their full valence electron shells, making them highly stable and chemically inert. This stability explains their lack of reactivity under normal conditions.

• Full Valence Shell: Most noble gases have eight electrons in their outermost shell (except helium, which has two).

• Low Reactivity: Their stable electron configuration means they rarely form chemical bonds.

• Example: Helium (He), Neon (Ne), and Argon (Ar) are common noble gases.

Chemical Reactions

Balancing Chemical Equations

Balancing chemical equations ensures the Law of Conservation of Mass is obeyed: atoms are neither created nor destroyed in a chemical reaction. Each side of the equation must have the same number of each type of atom.

• Unbalanced Equation:

• Balanced Equation:

• Explanation: By adding coefficients, we ensure there are 4 hydrogen atoms and 2 oxygen atoms on both sides of the equation.

Acids, Bases, and the pH Scale

Identifying Acids and Bases

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or basicity. The scale ranges from 0 to 14.

• Acidic Solutions: pH less than 7 (red/orange on indicators); high concentration of H+ ions.

• Neutral Solutions: pH of 7 (green); equal concentration of H+ and OH- ions.

• Basic (Alkaline) Solutions: pH greater than 7 (blue/purple); low concentration of H+ ions.

• Example: A solution with pH 2 is a strong acid.