Chemistry Chapter: Periodic Table & Electron Configs

Structure of the Periodic Table

• Organized into groups (columns) and periods (rows).
• Groups contain elements with similar chemical properties; numbered 1 to 18.
• Periods represent energy levels of electrons; numbered 1 to 7.
• Metals are located on the left side and in the center, characterized by luster, conductivity, and ductility.
• Nonmetals are found on the right side, generally poor conductors and often brittle in solid form.
• Metalloids (semi-metals) are located along the zig-zag line between metals and nonmetals, exhibiting mixed properties.

Electron Configurations

• Electron configurations describe the distribution of electrons among atomic orbitals.
• Follow the Aufbau principle, filling from lower to higher energy levels:
  • Example: Oxygen (O) - 1s² 2s² 2p⁴.
• For ions, adjust configurations based on the charge; cations lose electrons, anions gain:
  • Example: Na⁺ - 1s² 2s² 2p⁶ (loses one electron).

Definitions of Ions

• Ion: An atom or molecule with a net electric charge due to loss or gain of one or more electrons.
• Anion: A negatively charged ion, formed by gaining electrons (e.g., Cl⁻).
• Cation: A positively charged ion, formed by losing electrons (e.g., Na⁺).
• Monatomic Ion: An ion consisting of a single atom (e.g., Na⁺).
• Polyatomic Ion: An ion made up of two or more atoms bonded together (e.g., SO₄²⁻).

Formation of Ions

• Ions are formed through ionization, which involves the transfer of electrons between atoms.
• Metals tend to lose electrons and form cations.
• Nonmetals tend to gain electrons and form anions.

Valence of Common Ions

• Valence indicates the ability of an atom to bond based on its electron configuration.
• Common ions include:
  • Na⁺: valence of +1
  • Cl⁻: valence of -1
  • Ca²⁺: valence of +2
  • SO₄²⁻: valence of -2

Ionic Formula

• An ionic formula represents the ratio of ions in the compound.
• It is determined by balancing the total positive charge with total negative charge.
• Example: NaCl consists of Na⁺ and Cl⁻ in a 1:1 ratio.

Law of Conservation of Mass

• States that mass is neither created nor destroyed in a chemical reaction.
• The total mass of reactants equals the total mass of products.

Salt Formed in Neutralization Reactions

• A neutralization reaction between an acid and a base produces a salt and water.
• Example: From hydrochloric acid (HCl) and sodium hydroxide (NaOH), sodium chloride (NaCl) is formed.

Exothermic and Endothermic Reactions

• Exothermic Reactions: Release heat to the surroundings (e.g., combustion of methane).
• Endothermic Reactions: Absorb heat from the surroundings (e.g., photosynthesis).

Classification of Reactions

• Acid + Metal: Produces salt and hydrogen gas (e.g., HCl + Mg → MgCl₂ + H₂).
• Acid + Base: Produces salt and water (e.g., HCl + NaOH → NaCl + H₂O).
• Acid + Carbonate: Produces salt, water, and carbon dioxide (e.g., HCl + CaCO₃ → CaCl₂ + H₂O + CO₂).
• Combustion: Reaction of a substance with oxygen, producing carbon dioxide and water.
• Combination/Synthesis: Two or more substances combine to form one product (e.g., A + B → AB).
• Decomposition: A compound breaks down into simpler substances (e.g., AB → A + B).