CH week 2 lecture 1

Structure of the Atom

• Basic Concept: The structure of the atom is foundational to understanding chemical behavior. Key components include protons, neutrons, and electrons, with emphasis on the arrangement of electrons influencing chemical properties.

• Protons and Neutrons: Protons are positively charged particles located in the nucleus, while neutrons are neutral particles within the nucleus. The atomic number (Z) represents the number of protons, which also determines the number of electrons in a neutral atom.

• Electrons: Electrons are negatively charged and orbit the nucleus, occupying a substantial volume compared to the nucleus itself, which contains nearly all the atom's mass.

Atomic Mass Number

• Definition: The atomic mass number (A) is the total count of protons and neutrons in an atom. This number reflects the mass of the entire atom and is critical for calculations in chemistry.

• Periodic Trends: As one moves across the periodic table, elements transition from metallic to non-metallic properties. Most elements are metals, while nonmetals are located on the right side. Hydrogen presents unique challenges, exhibiting characteristics of both nonmetals and metals under varying conditions.

Electrons and Chemical Behavior

• Electrons and Valence Shells: The electrons in the outermost shell (valence shell) are crucial for bonding and chemical interactions. The number of electrons in this shell determines the element's reactivity.

• Octet Rule: Many elements seek to achieve a full valence shell, generally aiming for eight electrons (octet). However, some light elements like helium have two electrons and must be understood differently.

Bonding Preferences

• Metals vs. Nonmetals: Metals typically lose electrons to achieve a noble gas configuration (often resembling the previous period’s noble gas), while nonmetals tend to gain electrons to fill their outer shells.

• Ionic vs. Covalent Bonding: The transfer of electrons characterizes ionic bonding, typically between metals and nonmetals, resulting in cations (positively charged) and anions (negatively charged). In contrast, covalent bonding involves sharing electrons, typically between nonmetals.

Nomenclature in Chemistry

• Ionic Compounds: When naming ionic compounds, the cation retains its name, while the anion undergoes a modification by adopting the -ide suffix (e.g., chloride for chlorine).

• Polyatomic Ions: Elements can form polyatomic ions, which are groups of atoms that behave as a single charged entity (e.g., sulfate). Understanding these is crucial for naming and predicting compounds associated with them.

Naming Compounds

• Binary Compounds: For two nonmetals, the first element retains its name while the second receives the -ide suffix. Greek prefixes (mono-, di-, tri-, etc.) help indicate the number of atoms (e.g., carbon dioxide for CO2).

• Common Practice: In chemical formulas, the absence of the subscript ‘1’ indicates that there is one atom of that element. Naming conventions tend to simplify the representation of compounds to facilitate understanding.