Atoms, Bonding, and Organic Reaction Mechanisms

Comprehensive vocabulary flashcards covering atomic theory, molecular geometry, hybridisation, isomerism, and organic reaction mechanisms based on the lecture notes.

Rutherford's Nuclear Atom Model

A model proposing that the nucleus is at the center of the atom containing protons ($+$ charge) and neutrons (no charge), with negatively charged electrons orbiting around the outside.

The Quantum Mechanical Atom (Bohr)

A model proposing that electrons exist at specific allowed distances from the nucleus and cannot orbit anywhere they like.

Quantisation

The concept from the Bohr model that electrons can only have certain specific energies and not anything in between.

Wave-particle duality

The principle that electrons behave like a particle at some times and like a wave at other times.

Heisenberg Uncertainty Principle

The principle stating that it is impossible to know exactly where an electron is and how fast it is moving at the same time.

Ground state

The default stable position where an electron is at its lowest possible energy level and closest to the nucleus.

Excited state

A state where an electron has absorbed energy and jumped to a higher energy level.

Orbitals

Regions of space where an electron is most likely to be found, based on the Heisenberg Uncertainty Principle.

s orbitals

Sphere-shaped orbitals with one orbital per energy level, holding a maximum of $2$ electrons.

p orbitals

Dumbbell-shaped orbitals with three per energy level ($p_x$, $p_y$, $p_z$), holding a maximum of $6$ electrons.

d orbitals

Complex, clover-shaped orbitals with five per energy level, holding a maximum of $10$ electrons.

Electron configuration

The arrangement of electrons in orbitals, such as $1s^2 2s^2 2p^2$ for Carbon.

Valence Electrons

The outermost electrons of an atom that are responsible for all chemical bonding.

Covalent Bonds

Bonds formed by the sharing of valence electrons between atoms.

Octet Rule

The rule stating that atoms try to end up with $8$ electrons around them when forming bonds.

Expanded Octets

The ability of heavier elements like phosphorous ($P$) and sulfur ($S$) to hold more than $8$ electrons.

Lone pairs

Electrons in a Lewis structure that belong to just one atom and are not shared.

Formal charge formula

$$\text{Formal charge} = \text{valence electrons} - \text{lone pair electrons} - \frac{1}{2}(\text{bonding electrons})$$

Resonance

A phenomenon where a double bond can be placed in more than one location in a Lewis structure, as seen in nitrate ($\text{NO}_3^-$) or benzene.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory, which states that electron pairs repel each other and arrange themselves as far apart as possible to determine molecular shape.

Electron domains

The number of regions of electron density around a central atom (single, double, triple bonds, or lone pairs) used to determine shape.

Tetrahedral

The molecular shape formed with $4$ electron domains and a bond angle of $109^\text{o}$.

Sigma ($\sigma$) bond

A single bond formed by the overlap of orbitals (typically $s$-type) that sits directly between two nuclei.

Pi ($\pi$) bond

A bond formed by sideways overlap of $p$ orbitals where electrons sit above and below the two atoms; it exists only on top of a sigma bond.

Hybridisation

The process where an atom mixes its orbitals (such as $1 \times s$ and $3 \times p$) to create a new set of identical orbitals.

$sp^3$ Hybridisation

The blending of $1 \times s$ and $3 \times p$ orbitals to form $4$ identical orbitals, resulting in a tetrahedral shape ($109^\text{o}$).

$sp^2$ Hybridisation

The blending of $1 \times s$ and $2 \times p$ orbitals to form $3$ identical orbitals, leaving one $p$ orbital to form a pi bond, resulting in a trigonal planar shape ($120^\text{o}$).

$sp$ Hybridisation

The blending of $1 \times s$ and $1 \times p$ orbitals to form $2$ identical orbitals and leaving two $p$ orbitals for pi bonds, resulting in a linear shape ($180^\text{o}$).

Constitutional Isomers

Molecules with the same atomic formula but whose atoms are connected in a different order.

Stereoisomers

Molecules with the same atoms and connections but a different 3D arrangement in space.

Z isomer

A stereoisomer where the higher priority groups (based on atomic number) are on the same side of a double bond.

E isomer

A stereoisomer where the higher priority groups (based on atomic number) are on opposite sides of a double bond.

Chirality

The property of a molecule that has a mirror image that is different (non-superimposable) from itself.

Stereocentre

A carbon atom with $4$ completely different groups attached to it.

Enantiomers

Two mirror-image molecules that are identical in physical properties (melting/boiling point, color) but interact differently with light and other chiral objects.

Racemic Mixture

A mixture containing equal amounts of both enantiomers, denoted as ($\pm$), which does not rotate plane polarised light.

Diastereomers

Stereoisomers that are not mirror images of each other and have different physical properties; calculated using the formula $2^n$ for $n$ chiral carbons.

Homolytic Bond Cleavage

Bond breaking where the electrons split equally and each atom receives one electron, forming radicals.

Heterolytic Bond Cleavage

Bond breaking where both electrons go to one atom, resulting in the formation of ions.

Electrophile

An electron-poor species ($\delta+$) that is attracted to electrons.

Nucleophile

An electron-rich species with spare electrons that is willing to donate them to an electrophile.

$S_N2$ Reaction

Substitution, Nucleophilic, 2nd order; a one-step reaction where a nucleophile attacks and a leaving group departs simultaneously, causing inversion of configuration.

$S_N1$ Reaction

Substitution, Nucleophilic, 1st order; a two-step reaction where the leaving group departs first to form a carbocation intermediate before the nucleophile attacks.

Carbocation

A positively charged, trigonal planar carbon intermediate that is flat and extremely reactive.

Markovnikov's Rule

The rule stating that in the addition of $H-X$ to an unsymmetrical alkene, the $H^+$ adds to the carbon atom that already has more hydrogen atoms.

Bromonium ion

A three-membered ring intermediate containing a bridging $Br^+$ ion, which results in anti-addition during bromination.