Bonding in Chemistry

Ionic vs. Covalent Bonding

Atoms form chemical bonds to achieve greater stability, typically by attaining a full valence shell of electrons. The two main types of bonds are ionic and covalent bonds, distinguished by how electrons are handled between atoms.

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

• Covalent Bonds: Formed when two atoms share pairs of electrons, allowing both to fill their outer shells. This typically occurs between two non-metals.

• Example: Sodium chloride (NaCl) is an ionic compound, while water (H2O) is 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: For sodium, the atomic number is 11 (11 protons).

• Mass Number: For sodium with 11 protons and 12 neutrons, the mass number is .

• Example: Sodium (Na) is identified by atomic number 11 and mass number 23.

Chemical Stability

The Stability of Noble Gases

Noble gases (Group 18 of the periodic table) are characterized by their full valence electron shells, making them chemically inert and unlikely to form bonds.

• Key Point: Noble gases have 8 valence electrons (except Helium, which has 2), resulting in maximum stability.

• Example: Argon, Neon, and Helium rarely react with other elements.

Chemical Reactions

Balancing Chemical Equations

Balancing chemical equations ensures the Law of Conservation of Mass is followed: atoms are neither created nor destroyed in a chemical reaction.

• Unbalanced Equation:

• Balanced Equation:

• Explanation: The coefficients are adjusted so that the number of atoms of each element is equal 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 in a solution, indicating whether it is acidic, neutral, or basic (alkaline).

• Acidic: pH 0–6 (high concentration of H+ ions; red/orange color)

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

• Basic (Alkaline): pH 8–14 (low concentration of H+ ions; blue/purple color)

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

Summary Table: Types of Chemical Bonds

Summary Table: pH Scale Classification