NCEA Chemistry 3.4 and Entropy Vocabulary

Comprehensive vocabulary flashcards covering key terms and concepts from NCEA Chemistry 3.4 and Entropy notes.

Atomic Number

The unique identifier for each element, representing the total number of protons in a neutral atom.

Mass Number

The total number of protons and neutrons together in an atom's nucleus.

Orbital

An area of space with a high probability of finding a particular electron pair, where electrons orbit in pairs spinning in opposite directions.

Aufbau Principle

The principle stating that electrons always fill the subshells with the lowest energy level first.

Hund's Rule

The rule stating that the most stable arrangement is for sublevels to be filled with a single electron first (with the same direction spin) before pairing electrons.

Atomic Radius

Half the distance between the nuclei of two bonded atoms.

First Ionisation Energy

The energy required to remove one mole of electrons from the outside valence shell of 1 mole of atoms in a gaseous state.

Electronegativity

The tendency of an atom to attract bonding electrons from another atom.

Coulomb's Law

An inverse square law expressed as $F = \frac{k Q q}{r^2}$ that characterises electrostatic bonding based on charge and distance.

Octet Rule

The rule in drawing Lewis structures stating that each atom has eight electrons associated with it, except for hydrogen which has two.

Expanded Octet

A feature in third row elements and higher where central atoms have more than four valence shell orbitals filled with non-bonding pairs and/or bond pairs.

Rule of Orbitals

The rule stating that the total number of non-bonding pairs and bond pairs cannot exceed the number of valence shell orbitals, calculated as $\text{VSO} = n^2$, where $n$ is the row of the periodic table.

Dative Bond

A single covalent bond formed when one atom donates both electrons in the bonding pair.

Valence Shell Electron Pair Repulsion (VSEPR) Theory

A theory predicting molecular shape based on the principle that electron pairs (regions of negative charge) repel each other and move as far apart as possible around a central atom.

Trigonal Planar Shape

A molecular shape formed by 3 regions of negative charge around a central atom with 0 non-bonding pairs and bond angles of $120^\text{o}$.

Tetrahedral Shape

A 3-dimensional molecular shape formed by 4 regions of negative charge around a central atom with 0 non-bonding pairs and bond angles of $109.5^\text{o}$.

Trigonal Bipyramid Shape

A 3-dimensional molecular shape formed by 5 regions of negative charge around a central atom with 0 non-bonding pairs, having central bond angles of $120^\text{o}$ and vertical bond angles of $180^\text{o}$.

Octahedral Shape

A molecular shape formed by 6 regions of negative charge around a central atom with 0 non-bonding pairs, with central bond angles of $120^\text{o}$ and vertical regions at $180^\text{o}$.

Ionic Bonding

Bonding formed when one atom completely takes valence electrons from another to form ions held together by electrostatic attraction.

Covalent Bonding

Bonding that occurs when electron pairs are shared between neighbouring atoms with similar electronegativities.

Intramolecular Forces

The strong bonding forces within a molecule, such as covalent bonds holding atoms together.

Intermolecular Forces

The weak bonding forces between molecules due to attractions between partial charges.

Instantaneous Dipole Attraction

A temporary dipole attraction occurring in all atoms and molecules caused by the unsymmetrical rapid movement of electrons at any one instant.

Permanent Dipole Attraction

An intermolecular attraction occurring between polar molecules due to an imbalance of charge caused by electronegativity differences.

Hydrogen Bonding

A special, strong type of permanent dipole attraction occurring when hydrogen is bonded directly to N, O, or F.

Enthalpy

The energy in a substance due to the kinetic energy of particles and potential energy in chemical bonds, represented by $H$.

Exothermic Reaction

A reaction that releases heat energy into the surroundings, resulting in an increase in surrounding temperature and a negative enthalpy change (\text{\textDelta} H < 0).

Endothermic Reaction

A reaction that absorbs heat energy from the surroundings, resulting in a decrease in surrounding temperature and a positive enthalpy change (\text{\textDelta} H > 0).

Standard Enthalpy of Combustion

The enthalpy change when one mole of an element or compound reacts completely with oxygen under standard conditions, denoted as \text{\textDelta}_c H^\text{o}.

Standard Enthalpy of Formation

The enthalpy change when one mole of a substance is formed from its constituent elements under standard conditions, denoted as \text{\textDelta}_f H^\text{o}.

Standard Conditions

Experimental conditions for thermochemical measurements defined as a temperature of $25\text{ }^\text{o}\text{C}$, pressure of $1\text{ }\text{ATM}$, and concentration of $1\text{ }\text{mol}\text{ }\text{L}^{-1}$.

Entropy

A measure of the disorder, random motion of particles, or dispersal of matter and energy in a system, denoted by $S$.

Hess's Law

The principle stating that if an overall reaction can be broken down into a series of steps, the overall enthalpy of reaction is the sum of the enthalpies of the individual reaction steps.

Specific Heat Capacity

The amount of heat energy required to raise the temperature of a given mass of a substance, represented as $c$ (e.g., 4.18\text{ }\text{J}\text{ }\text{^\text{o}C}^{-1}\text{ }\text{g}^{-1} for water).

Spontaneous Reaction

A reaction that favours the formation of products under existing conditions without needing to be driven by a continual input of energy.

Total Entropy Change

The sum of the entropy change of the system and surroundings, calculated as \text{\textDelta} S_{\text{total}} = \text{\textDelta} S_{\text{system}} + \text{\textDelta} S_{\text{surroundings}}, which must be positive for a process to be spontaneous.

Standard Gibbs Free Energy Change

An energy value calculated using $\Delta G = \Delta G^\circ + RT \ln Q$ , where a negative value (\text{\textDelta} G^\text{o} < 0) indicates a spontaneous reaction.