General Chemistry
"Future Chemist! Atoms, Molecules, and Reactions. Chemistry is everywhere - from the food we eat to the medicines we take. Master stoichiometry at gas laws para sa college chemistry!"
1 Atomic Structure and Electron Configuration
Subatomic Particles
| Particle | Charge | Location | Mass (amu) |
|---|---|---|---|
| Proton | +1 | Nucleus | 1 |
| Neutron | 0 | Nucleus | 1 |
| Electron | -1 | Orbitals | ~0 |
Electron Configuration Rules
- Aufbau Principle: Fill lowest energy first
- Pauli Exclusion: Max 2 electrons per orbital
- Hund's Rule: Fill orbitals singly first
Order: 1s 2s 2p 3s 3p 4s 3d 4p 5s...
2 Chemical Bonding
Ionic Bond
Transfer of electrons (metal + nonmetal)
- • High melting point
- • Conducts when dissolved
- • Forms crystals
- • Example: NaCl
Covalent Bond
Sharing of electrons (nonmetal + nonmetal)
- • Lower melting point
- • Poor conductor
- • Forms molecules
- • Example: H₂O, CO₂
Metallic Bond
Sea of electrons (metal + metal)
- • Good conductor
- • Malleable/ductile
- • Lustrous
- • Example: Fe, Cu
3 The Mole Concept and Stoichiometry
Avogadro's Number
1 mole = 6.022 × 10²³ particles
Applies to atoms, molecules, ions, or any particles
Molar Mass
Mass of 1 mole of substance (g/mol)
- Formula: n = m / M
- n = moles, m = mass (g), M = molar mass
Molar Volume (Gas at STP)
Volume of 1 mole of gas at STP
22.4 L/mol at STP
STP: 0°C (273K) and 1 atm
4 Balancing Chemical Equations
Law of Conservation of Mass:
Atoms cannot be created or destroyed - same number on both sides!
Steps to Balance
- Write the unbalanced equation
- Count atoms of each element on both sides
- Add coefficients to balance (start with metals, then nonmetals)
- Balance hydrogen and oxygen last
- Verify: same number of each atom on both sides
Example:
Unbalanced: Fe + O₂ → Fe₂O₃
Balanced: 4Fe + 3O₂ → 2Fe₂O₃
5 Gas Laws
| Law | Formula | Constant | Relationship |
|---|---|---|---|
| Boyle's Law | P₁V₁ = P₂V₂ | T, n | P ↑ V ↓ (inverse) |
| Charles' Law | V₁/T₁ = V₂/T₂ | P, n | V ↑ T ↑ (direct) |
| Gay-Lussac's | P₁/T₁ = P₂/T₂ | V, n | P ↑ T ↑ (direct) |
| Combined | P₁V₁/T₁ = P₂V₂/T₂ | n | Combines all three |
| Ideal Gas | PV = nRT | - | R = 0.0821 L·atm/mol·K |
Important: Always convert temperature to Kelvin!
K = °C + 273
6 Types of Chemical Reactions
-
Synthesis (Combination):
A + B → AB
Example: 2H₂ + O₂ → 2H₂O
-
Decomposition:
AB → A + B
Example: 2H₂O → 2H₂ + O₂
-
Single Replacement:
A + BC → AC + B
Example: Zn + CuSO₄ → ZnSO₄ + Cu
-
Double Replacement:
AB + CD → AD + CB
Example: NaCl + AgNO₃ → NaNO₃ + AgCl
-
Combustion:
Fuel + O₂ → CO₂ + H₂O
Example: CH₄ + 2O₂ → CO₂ + 2H₂O
-
Acid-Base:
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O
7 Solutions and Concentration
Concentration Units
- Molarity (M): moles solute / L solution
- Molality (m): moles solute / kg solvent
- % by mass: (mass solute / mass solution) × 100
- ppm: parts per million = mg/L
Dilution Formula
M₁V₁ = M₂V₂
When diluting a solution, moles of solute remain constant
Practice Questions
1. How many moles are in 36 grams of water (H₂O)?
Show Answer
2 moles. Molar mass of H₂O = 2(1) + 16 = 18 g/mol. n = 36g ÷ 18 g/mol = 2 mol.
2. A gas has volume 4L at 2 atm. What is its volume at 8 atm (constant T)?
Show Answer
1 L. Using Boyle's Law: P₁V₁ = P₂V₂ → (2)(4) = (8)(V₂) → V₂ = 1 L.
3. Balance: ___CH₄ + ___O₂ → ___CO₂ + ___H₂O
Show Answer
1CH₄ + 2O₂ → 1CO₂ + 2H₂O. Check: C=1, H=4, O=4 on both sides.
4. What is the molarity of a solution with 2 moles NaCl in 500 mL?
Show Answer
4 M. M = moles/L = 2 mol ÷ 0.5 L = 4 M.
Exam Tips for General Chemistry
- ✓ Memorize Avogadro's number: 6.022 × 10²³
- ✓ Gas laws: Always convert to Kelvin first (K = °C + 273)
- ✓ Balancing: Start with metals, end with H and O
- ✓ PV = nRT: R = 0.0821 L·atm/mol·K (memorize this!)
- ✓ Mole conversions: Use molar mass, Avogadro's number, and molar volume (22.4 L at STP)
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