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General Chemistry Study Notes: Atomic Structure, Electron Configuration, Bonding, and Molecular Properties

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Atomic Structure

Atoms and Isotopes

Atoms are the basic units of matter, composed of protons, neutrons, and electrons. The atomic number of an atom is equal to the number of protons, while the mass number is the sum of protons and neutrons.

  • Atomic Number (Z): Number of protons in the nucleus.

  • Mass Number (A): Number of protons plus neutrons.

  • Isotopes: Atoms of the same element with different numbers of neutrons.

Example: Hydrogen has three isotopes: Hydrogen (1 proton), Deuterium (1 proton, 1 neutron), and Tritium (1 proton, 2 neutrons).

  • Ions: Atoms that have gained or lost electrons. Positively charged ions are cations, negatively charged ions are anions.

Example: Proton (H+) vs. Hydride (H-).

Electron Configuration

Ground State Electron Configuration

Electron configuration describes the distribution of electrons among the orbitals of an atom using the Aufbau Principle, Pauli Exclusion Principle, and Hund's Rule.

  • Aufbau Principle: Electrons fill the lowest energy orbitals first.

  • Pauli Exclusion Principle: No two electrons in an atom can have the same set of quantum numbers.

  • Hund's Rule: Electrons occupy orbitals singly before pairing.

Condensed Electron Configuration: Uses the previous noble gas to abbreviate the configuration.

Example: Phosphorus (Z = 15): Ground state: Condensed:

Block

Elements

s-block

Groups 1A, 2A

p-block

Groups 3A-8A

d-block

Transition metals

f-block

Lanthanides & Actinides

Electronegativity

Periodic Trend

Electronegativity (EN): The ability of an atom to attract electrons in a chemical bond. Electronegativity increases from left to right across a period and from bottom to top within a group.

  • Most electronegative element: Fluorine (F)

  • Group 7A trend: Electronegativity increases up the group.

Example: Among Br, S, I, Cl, O, the most electronegative Group 7A element is Cl.

Octet Rule

Valence and Shared Electrons

The Octet Rule states that most main group elements tend to achieve eight electrons in their valence shell through chemical bonding.

  • Valence Electrons: Electrons in the outermost shell, involved in bonding.

  • Shared Electrons: Electrons shared between atoms in a chemical bond.

Formula: Electrons = Valence Electrons + Shared Electrons

Example: In methanol (CH3OH), oxygen has 6 valence electrons and 2 shared electrons.

Formal Charge

Calculating Formal Charge

Formal charge helps determine the most accurate Lewis structure for a molecule.

  • Formula:

  • Only allowable formal charges: -1, 0, +1

Example: For the thiocyanate ion (NCS-), calculate the formal charge for each atom using the formula above.

Lewis Dot Structures

Drawing Lewis Structures

Lewis Dot Structures represent the arrangement of valence electrons in molecules.

  1. Count total valence electrons.

  2. Place the least electronegative atom in the center (except hydrogen).

  3. Add electrons to outer atoms to satisfy the octet rule.

  4. Place remaining electrons on the central atom.

  5. If any atom lacks an octet, form double or triple bonds.

  6. Check formal charges to confirm the best structure.

Example: Draw the Lewis structure for COCl2.

Resonance Structures

Resonance and Resonance Hybrid

Resonance structures are multiple valid Lewis structures for a molecule with delocalized electrons.

  • Movement of electrons occurs in pi bonds or lone pairs.

  • Double-sided arrows indicate resonance between structures.

  • The true structure is a resonance hybrid of all possible resonance forms.

Example: Draw all resonance structures for the nitrate ion (NO3-).

Hybridization

Electron Groups and Hybrid Orbitals

Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals suitable for bonding.

  • Electron Groups: Number of bonds and lone pairs around the central atom.

Electron Groups

Geometry

Hybridization

Example

2

Linear

sp

CO2

3

Trigonal Planar

sp2

BF3

4

Tetrahedral

sp3

CH4

Example: HCN has linear geometry and sp hybridization.

Molecular Polarity

Polar and Nonpolar Molecules

Molecular polarity arises from the distribution of electron density in a molecule.

  • Nonpolar Molecule: Hydrocarbons or molecules with perfect symmetry and no lone pairs on the central atom.

  • Polar Molecule: Molecules with an asymmetric shape or lone pairs on the central atom.

Electron Groups

Lone Pairs

Polarity

2

0

Nonpolar

3

1

Polar

4

2

Polar

Example: Nitrogen trifluoride (NF3) is polar due to lone pairs on the central atom.

Functional Groups

Recognizing Functional Groups

Functional groups are specific groups of atoms within molecules responsible for characteristic chemical reactions.

  • Hydrocarbons: Alkanes, alkenes, alkynes, aromatic compounds.

  • With Carbonyls: Aldehyde, ketone, acid chloride, amide, carboxylic acid, ester.

  • Without Carbonyls: Alkyl halide, amine, alcohol, ether, thiol.

Example: Identify functional groups in given organic molecules.

Organic Chemistry Introduction

Organic Molecules and Hydrocarbons

Organic chemistry studies molecules containing carbon and hydrogen, often with other elements. Organic molecules are defined by the presence of both carbon and hydrogen. Hydrocarbons contain only carbon and hydrogen.

  • Example: Identify which molecules are organic and which are hydrocarbons.

Additional info:

  • Some context and examples were expanded for clarity and completeness.

  • Tables were recreated and summarized based on the images and text provided.

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