🔬 Chemistry Study Guide: Key Concepts & Rules
🧪 Subatomic Particles
- Protons: +1 charge
- Neutrons: 0 charge (neutral)
- Electrons: –1 charge
💡 Protons define the element, electrons control reactivity.
🔋 Electron Energy Levels
- Electrons absorb energy to move to higher shells (excited state).
- Higher shells = more energy.
🔁 Isotopes
- Same number of protons, different number of neutrons.
- Example:
- Carbon-12 → 6 protons, 6 neutrons
- Carbon-13 → 6 protons, 7 neutrons
🔗 Compounds vs. Elements
- Compound = 2+ different elements chemically combined (e.g. NaCl).
- Not physically combined.
- Only one type of atom (same atomic number) = element.
⚖️ Conservation in Reactions
- Mass is always conserved.
- Molecules and atoms rearrange—not necessarily conserved.
⚠️ Ignore terms like “erosity”—not scientifically valid.
🔩 Bonding Concepts
- Metallic bonds = metals involved.
- Forming bonds = energy released.
- Breaking bonds = energy absorbed.
- Carbon can form chains, rings, and networks.
🔥 Catalysts & Activation Energy
- Catalyst = speeds up a reaction by lowering activation energy.
⚠️ Incorrect: catalysts do not increase activation energy.
🌡️ States of Matter & Behavior
- Solids (e.g. NaCl) have constant composition and properties.
- Higher temperature = higher kinetic energy.
- Ideal gas conditions = high temp, low pressure; particles act independently.
- Distillation separates compounds by boiling point.
⚛️ Atomic Radius
- Lose an electron → radius decreases.
- Gain an electron → radius increases.
♻️ Equilibrium
- At chemical equilibrium, concentrations of reactants and products remain constant (not necessarily equal).
⚡ Electronegativity & Electron Behavior
- Electronegativity = strength of atom’s attraction for bonding electrons.
- Electrons are central to reactivity and bond behavior.
🌀 Entropy
- Entropy = measure of disorder or randomness.
🧠 Think of a messy room or chaotic crowd.
📚 References