Chemistry Lecture Review

Periodic Table Groups

• Group 1 to Group 2: Elements in these groups (1A - 2A) typically have easily defined valence electrons. E.g., Group 1 (alkali metals) has 1 valence electron, Group 2 (alkaline earth metals) has 2.
• Transition Metals: Behavior is variable; valence electrons often indicated by Roman numerals (e.g., iron (III)).

Group 17 Elements (Halogens)

• Group 17 (7A): They aim to gain 1 electron to achieve a stable octet, making them highly reactive.
• Chlorine Example: Has 7 valence electrons and does not want to lose any; it seeks to gain 1 electron to complete its outer shell.

Atomic Behavior

• Argon (Group 18): Noble gas with a complete outer shell (8 electrons), thus chemically inert; does not bond easily with other elements such as sodium.
• Sodium (Group 1): Possesses 1 valence electron that it readily loses to achieve stability.

Chemical Bonding Concepts

• Ionization Energy: The energy required to remove an electron. Chlorine has a high ionization energy due to its valence structure.
• Electronegativity: Measures an atom's ability to attract electrons. Chlorine also has high electronegativity.

Electron Dot Diagrams

• Chlorine Example: Drawn as D11 (where D1 represents shell electrons).
  • First shell: 2 electrons.
  • Second shell: 8 electrons.
  • Third shell: 7 electrons need to gain one to achieve 8.

Cations and Anions

• Cation: Positively charged ion (e.g., Lithium loses 1 electron to form a cation).
• Anion: Negatively charged ion (e.g., Oxygen gains 2 electrons to form an anion).

Forming Compounds with Crisscross Method

• Aluminum Oxide Example:
  • Aluminum has 3 valence electrons (loses 3) to form a cation: $Al^{3+}$.
  • Oxygen has 6 valence electrons (gains 2) to form an anion: $O^{2-}$.
  • Crisscrossing yields the formula: $Al2O3$ (2 Al for every 3 O).

Covalent Bonds

• Polar Covalent Bonds: Unequal sharing of electrons (e.g., HCl).
  • Hydrogen (lower electronegativity) is partially positive, while Chlorine is partially negative due to higher electronegativity differences.

Hydrogen Bonding in Water

• Water Molecule (H2O): Polar molecule due to oxygen's higher electronegativity.
  • This creates regions of partial positivity on hydrogens and partial negativity on oxygen, enabling hydrogen bonds between molecules.

Hydrocarbons

• Types:
  • Alkanes: Saturated hydrocarbons with only single bonds (e.g., CnH2n+2).
  • Alkenes: At least one double bond (not saturated).
  • Alkynes: Contain one triple bond.

Valence Electrons and Bond Formation

• Nitrogen (5 Valence Electrons): Tends to gain 3 electrons and forms covalent bonds, resulting in polar covalent characteristics.

Carbohydrates and Lipids

• Carbohydrates: Consist of carbon (C) and hydrogen (H), often found in ring structures (hexagons).
• Lipids: Composed of hydrocarbon chains, which can be saturated (no double bonds) or unsaturated (with double bonds).

Amino Acids

• Basic Structure: Composed of amine group, carboxyl group, and variable R (side chain).
• Functionality: Building blocks of proteins; R group determines specific properties of the amino acid.

Summary of Key Concepts

• Throughout, remember the relationships between valence electrons, ionization energy, electronegativity, and how they contribute to the chemical properties and bonding behavior of elements.