Lecture Notes on Atoms, Elements, and Chemical Reactions

Introduction to Atoms

• Everything is made of atoms, including humans.
• Atoms consist of a core (protons and neutrons) and electrons.
• Different elements are defined by the number of protons in the core.
• Example: Water is made of Hydrogen and Oxygen.

Atomic Structure

• Quantum mechanics gives a more accurate depiction of atoms.
• Atoms have multiple electron “shells”.
• Valence electrons are in the outermost shell and play a key role in chemistry.

Periodic Table

• Elements listed in the periodic table.
• Elements in the same column (group) have the same number of valence electrons.
• Main groups: Group number = number of valence electrons (exceptions exist).
• Similar valence electrons = similar chemical behavior.
• Example: Alkali metals (Group 1, excluding hydrogen) have one valence electron, are shiny, soft.
• Elements in the same row (period) have the same number of shells; shell number increases from top to bottom.
• Atomic mass increases from left to right; new proton, electron, and neutrons added.

Isotopes and Ions

• Different neutrons = different isotopes, some are unstable and release ionizing radiation.
• Atoms with equal protons and electrons have no charge.
• Atoms with more or fewer electrons than protons become ions (anions = negative, cations = positive).

Bonding and Molecules

• Two or more atoms bonded = molecule.
• Two or more different elements bonded = compound.
• Compounds often behave differently than their constituent elements.
• Example: Sodium and Chlorine form table salt.
• Molecular formulas and isomers.
• Lewis-Dot-Structures for representing valence electrons and bonds.

Chemical Bonds

• Bonds form to reach a state of lower energy (full outer shell).
• Noble gases have full outer shells and are less reactive.
• Covalent bonds: electrons are shared between atoms.
• Electronegativity: strength of an atom to attract electrons.
• Ionic bonds form between atoms with large differences in electronegativity (e.g., Sodium Chloride).
• Metallic bonds: positive nuclei surrounded by mobile electrons.
• Polarity of bonds (nonpolar and polar covalent bonds).
• Intermolecular forces: including hydrogen bonds and Van der Waals forces.

States of Matter

• Three main states: solid, liquid, gas.
• Solids: tightly packed particles; Liquids: particles move freely but fixed volume; Gases: particles move freely.
• Temperature = average kinetic energy; Entropy = amount of disorder.

Chemical Reactions

• Reactions occur to reach a more stable state.
• Types of reactions: synthesis, decomposition, single replacement, double replacement.
• Stoichiometry: ratios in chemical reactions, conservation of mass.
• Physical vs. chemical changes.
• Activation energy required for reactions.
• Catalysts reduce activation energy and are reusable.

Energy in Reactions

• Enthalpy: internal energy content of a system.
• Exothermic reactions release heat; endothermic reactions absorb heat.
• Gibbs Free Energy: accounts for enthalpy and entropy; determines spontaneity of reactions.
• Chemical equilibrium: reversible reactions at equal rates.

Acid-Base Chemistry

• Acids donate protons, bases accept protons.
• pH measures hydronium ion concentration; pH and pOH always add to 14.
• Strong acids and bases can neutralize each other.

Redox Reactions

• Reduction-Oxidation: transfer of electrons between atoms.
• Oxidation numbers indicate electron flow.
• Balancing redox reactions in acidic or basic solutions.

Quantum Mechanics and Electron Configuration

• Electrons described by four quantum numbers (n, l, ml, ms).
• Aufbau principle: order of filling subshells.
• Valence electrons can be inferred from electron configurations.

Summary

• Understanding of atoms, elements, chemical bonds, reactions, and states of matter is fundamental to chemistry.
• Periodic table as a useful tool for predicting chemical behavior and properties.
• Energy changes and equilibrium concepts are crucial in chemical processes.
• Quantum mechanics provides deeper insight into atomic structures and behaviors.

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