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

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Atomic Structure

Atoms and Isotopes

The atom is the fundamental unit of matter, consisting of protons, neutrons, and electrons. The atomic number 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 Isotopes

Isotope	Protons	Neutrons	Electrons
Hydrogen (¹H)	1	0	1
Deuterium (²H)	1	1	1
Tritium (³H)	1	2	1

Example: Hydrogen Ions

Ion	Protons	Neutrons	Electrons
Proton (H⁺)	1	0	0
Hydride (H⁻)	1	0	2

Additional info: Atoms with more electrons than protons are negatively charged (anions), while those with fewer are positively charged (cations).

Electron Configuration

Ground State Electron Configuration

Electron configuration describes the distribution of electrons among the orbitals of an atom, following 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 degenerate orbitals singly before pairing.

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

Example: Phosphorus (Z = 15)

Ground State:
Condensed:

Block	Groups
s-block	1A, 2A
p-block	3A-8A
d-block	Transition metals (3B-2B)

Electronegativity

Definition and Periodic Trend

Electronegativity (EN): A measure of an atom's ability to attract electrons in a chemical bond.

Periodic Trend: Electronegativity increases from left to right across a period and increases going up a group.
Most electronegative element: Fluorine (F).

Example: The most electronegative Group 7A element is Cl (Chlorine), but F (Fluorine) is the most overall.

Octet Rule

Valence and Shared Electrons

The Octet Rule states that 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.

Example: In H3COH, oxygen has 6 valence electrons and 2 shared electrons, achieving an octet.

Formal Charge

Calculating Formal Charge

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

Only allowable formal charges: -1, 0, +1
The sum of formal charges equals the overall charge of the molecule or ion.

Formula:

Example: For the thiocyanate ion (NCS-):

N (Group 5A):
C (Group 4A):
S (Group 6A):

Lewis Dot Structures

Drawing Rules

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

Count total valence electrons.
Place the least electronegative atom in the center (except H and F).
Add electrons to outer atoms to complete octets.
Place remaining electrons on the central atom.
If atoms lack octets, form double or triple bonds.
Check formal charges for stability.

Example: COCl2 (Phosgene)

Resonance Structures

Definition and Representation

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.
The true structure is a resonance hybrid, a composite of all resonance forms.

Example: Nitrate ion (NO3-) has three resonance structures.

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 sp hybridization and two unhybridized p orbitals.

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	1 or 2	Polar

Example: NF3 is polar due to lone pairs on the central atom.

Functional Groups

Definition and Classification

Functional Group: A specific group of atoms within a molecule responsible for characteristic chemical reactions.

Hydrocarbons: Alkanes, alkenes, alkynes, aromatic compounds.
With Carbonyls: Aldehydes, ketones, carboxylic acids, esters, amides, acid chlorides.
Without Carbonyls: Alkyl halides, amines, alcohols, ethers, thiols.

Functional Group	Structure
Alkane	R-CH3
Alkene	R-CH=CH-R'
Alkyne	R-C≡C-R'
Aromatic	Benzene ring
Alcohol	R-OH
Aldehyde	R-CHO
Ketone	R-CO-R'
Carboxylic Acid	R-COOH
Ester	R-COOR'
Amide	R-CONH2

Organic Chemistry Overview

Organic Molecules and Hydrocarbons

Organic chemistry studies molecules containing both carbon and hydrogen. Hydrocarbons are organic molecules composed solely of carbon and hydrogen.

Organic Molecule: Contains both carbon and hydrogen.
Hydrocarbon: Contains only carbon and hydrogen.

Example: Identify organic and hydrocarbon molecules from a list of structures.

Summary Table: Principles of Electron Configuration

Principle	Description
Aufbau Principle	Electrons fill lowest energy orbitals first.
Pauli Exclusion Principle	No two electrons have the same set of quantum numbers.
Hund's Rule	Electrons occupy degenerate orbitals singly before pairing.

Additional info: These notes cover foundational topics in general chemistry, including atomic structure, electron configuration, chemical bonding, molecular geometry, and basic organic chemistry concepts. They are suitable for college-level exam preparation.