Atomic Structure & Bonding

Ionic vs. Covalent Bonding

The nature of chemical bonds is fundamental to understanding how atoms combine to form compounds. The two primary types of bonds are ionic and covalent bonds, distinguished by how electrons are distributed between atoms.

• Ionic Bonds: Formed when one atom transfers electrons to another, resulting in the creation of oppositely charged ions. Typically occurs between a metal and a non-metal. The metal loses electrons to become a positively charged cation, while the non-metal gains electrons to become a negatively charged anion.

• Covalent Bonds: Formed when two atoms share pairs of electrons, allowing both to achieve a stable electron configuration. Usually 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 structure, specifically the number of protons and neutrons in its nucleus.

• Atomic Number: The number of protons in the nucleus of an atom. Determines the identity of the element. For example, an atom with 11 protons is sodium (Na).

• Mass Number: The sum of protons and neutrons in the nucleus. For sodium, with 11 protons and 12 neutrons, the mass number is $11 + 12 = 23$.

• Example: Sodium (Na) has an atomic number of 11 and a mass number of 23.

Chemical Stability

The Stability of Noble Gases

Noble gases (Group 18 elements) are characterized by their lack of chemical reactivity. This is due to their full valence electron shells, which make them energetically stable and unlikely to form bonds with other elements.

• Key Point: Noble gases have 8 electrons in their outer shell (except Helium, which has 2), making them chemically satisfied.

• Example: Argon, neon, and helium are noble gases that rarely participate in chemical reactions.

Chemical Reactions

Balancing Chemical Equations

Balancing chemical equations is essential to obey the Law of Conservation of Mass, which states that atoms are neither created nor destroyed in a chemical reaction.

• Unbalanced Equation: $H_2 + O_2 \rightarrow H_2O$

• Balanced Equation: $2H_2 + O_2 \rightarrow 2H_2O$

• Explanation: The balanced equation ensures there are equal numbers of hydrogen and oxygen atoms on both sides.

Acids and Bases

Identifying Acids and Bases Using the pH Scale

The pH scale is used to determine the acidity or basicity of a substance based on its hydrogen ion concentration.

• Acids: Substances with a pH less than 7. Strong acids have pH values closer to 0.

• Bases: Substances with a pH greater than 7. Strong bases have pH values closer to 14.

• Neutral: A pH of 7 indicates neutrality (e.g., pure water).

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

Additional info:

• The provided video link offers a visual comparison of ionic and covalent bonds, which may be useful for further study.