1. Understanding Compounds
2. The Role of the Periodic TableThe Periodic Table helps predict how elements combine based on their valency.
Valency:
3. Predicting the Ratio of Atoms in CompoundsStep 1: Identify the Elements and Their Valency:
- Definition: A compound is a substance formed when two or more elements chemically combine in a fixed ratio.
- Example: Water (H2OH_2OH2O) is formed by combining two hydrogen atoms with one oxygen atom.
2. The Role of the Periodic TableThe Periodic Table helps predict how elements combine based on their valency.
Valency:
- Valency is the combining power of an element, determined by the number of electrons in its outer shell.
- Elements tend to:
- Lose, gain, or share electrons to achieve a full outer shell (following the octet rule).
- Group 1 (Alkali Metals): Valency = 1 (e.g., Sodium NaNaNa).
- Group 2 (Alkaline Earth Metals): Valency = 2 (e.g., Magnesium MgMgMg).
- Group 13: Valency = 3 (e.g., Aluminium AlAlAl).
- Group 14: Valency = 4 (e.g., Carbon CCC).
- Group 15: Valency = 3 (e.g., Nitrogen NNN).
- Group 16: Valency = 2 (e.g., Oxygen OOO).
- Group 17 (Halogens): Valency = 1 (e.g., Chlorine ClClCl).
- Group 18 (Noble Gases): Valency = 0 (generally non-reactive).
3. Predicting the Ratio of Atoms in CompoundsStep 1: Identify the Elements and Their Valency:
- Example: Sodium (NaNaNa) has a valency of 1, and Chlorine (ClClCl) also has a valency of 1.
- Combine elements in a ratio that balances their valency.
- Example: Sodium chloride (NaClNaClNaCl) combines 1 sodium atom and 1 chlorine atom because both have valency 1.
- The formula shows the ratio of atoms in the compound.
- Example: In magnesium chloride (MgCl2MgCl_2MgCl2), 1 magnesium atom (valency 2) combines with 2 chlorine atoms (each with valency 1).