Chemistry Lecture Notes

Atoms and Elements

• Everything is made of atoms, including humans.
• Atoms consist of a core (protons and neutrons) and electrons.
• Number of protons determines the element.
• Electrons reside in 'shells'; valence electrons are in the outermost shell.
• Periodic table groups elements; similar valence electrons show similar chemical behavior.

Molecules and Compounds

• Two or more atoms form a molecule; different elements form a compound.
• Compounds exhibit behaviors different from their constituent elements.
• Molecular formulas indicate the number of atoms of each element.
• Isomers have the same formula but different structures.

Chemical Bonds

• Covalent Bonds: Electrons are shared between atoms.
  • Nonpolar covalent bonds share electrons equally.
  • Polar covalent bonds have unequal sharing due to electronegativity.
• Ionic Bonds: Electrons are transferred from one atom to another.
• Metallic Bonds: Electrons are delocalized among metal atoms.

Intermolecular Forces

• Hydrogen Bonds: Strong dipoles due to bonding with F, O, or N.
• Van der Waals Forces: Weak, temporary dipoles due to electron movement.

States of Matter

• Solids: Tightly packed structure; particles can only vibrate.
• Liquids: Fixed volume, but particles can move freely.
• Gases: Particles have enough energy to fill any volume.

Chemical Reactions

• Reactions occur to decrease energy and reach stability.
• Types include synthesis, decomposition, single and double replacement.
• Stoichiometry ensures balanced chemical equations.
• Physical vs. chemical changes: Chemical reactions involve changes in substances.

Energy in Reactions

• Activation Energy: Energy needed to start a reaction.
• Catalysts: Lower activation energy without being consumed.
• Enthalpy: Internal energy of a system.
  • Exothermic: Releases heat, spontaneous if enthalpy decreases.
  • Endothermic: Absorbs heat, requires continuous energy input.
• Gibbs Free Energy: Determines reaction spontaneity, considering enthalpy and entropy.

Acids, Bases, and pH

• Acids donate protons; bases accept protons.
• pH measures acidity based on hydronium ion concentration.
• Neutralization occurs when an acid and base form water and salt.

Quantum Mechanics and Electrons

• Electrons are described by four quantum numbers (n, l, ml, ms).
• Orbitals: Regions where electrons are likely to be found.
• Aufbau principle: Order of filling electron subshells.

Miscellaneous

• Redox Reactions: Involve transfer of electrons, changing oxidation states.
• Mixtures: Homogeneous (even distribution) vs. heterogeneous (distinct regions).
• Emission spectra: Elements emit light at specific frequencies.

Conclusion

• Chemistry involves understanding elements, their interactions, and energy changes.
• Staying engaged with content aids learning and exploration in chemistry.