Overview
This lecture covers the basics of chemical bonding, focusing on how elements achieve complete outer energy levels by gaining or losing electrons, and explains the concept of valency and the general behavior of metals and non-metals in bonding.
Metals and Non-Metals on the Periodic Table
- The periodic table is divided into metals (left side) and non-metals (right side).
- Hydrogen is a non-metal but appears on the left side of the periodic table.
Electron Configuration and Energy Levels
- Atoms have a nucleus with protons (positive) and neutrons (neutral), surrounded by electrons in energy levels.
- The row number (period) indicates the number of energy levels for an element.
- Example: Lithium (Li) has 3 electrons (2 in the first, 1 in the second level).
- Example: Sodium (Na) has 11 electrons (2, 8, 1 in three levels).
The Goal of Chemical Bonding
- Atoms react to achieve a complete outer energy level (octet rule).
- Atoms prefer the easier route: losing a few electrons is favored over gaining many, and vice versa.
Behavior of Specific Elements
- Group 1 (e.g., Li, Na): Lose 1 electron to complete their outer level.
- Group 2 (e.g., Be): Lose 2 electrons.
- Group 13 (e.g., B): Lose 3 electrons.
- Group 14 (e.g., C): Can gain or lose 4 electrons.
- Group 15 (e.g., N): Gain 3 electrons.
- Group 16 (e.g., O): Gain 2 electrons.
- Group 17 (e.g., F): Gain 1 electron.
- Group 18 (noble gases, e.g., Ne): Already complete, do not gain or lose electrons.
Valency Numbers
- Valency indicates the charge an atom acquires to complete its outer level.
- Group 1: +1 (lose 1 electron)
- Group 2: +2 (lose 2 electrons)
- Group 13: +3 (lose 3 electrons)
- Group 14: ±4 (can gain or lose 4 electrons)
- Group 15: –3 (gain 3 electrons)
- Group 16: –2 (gain 2 electrons)
- Group 17: –1 (gain 1 electron)
- Noble gases: 0 (do not react)
Trends for Metals and Non-Metals
- Metals (left side): Tend to lose electrons.
- Non-metals (right side): Tend to gain electrons.
Key Terms & Definitions
- Energy Level — The region around the nucleus where electrons are found.
- Octet Rule — Atoms aim for a full outer shell, usually 8 electrons.
- Valency — The charge an atom takes when completing its outer energy level.
- Noble Gases — Elements with full outer energy levels that do not react.
Action Items / Next Steps
- Review electron configurations of elements in groups 1–17.
- Prepare for next lesson, which will build on these bonding concepts.