A-Level Chemistry: Atomic Structure, Electron Configuration, and Periodicity

Vocabulary practice cards focusing on foundational chemistry definitions, mass spectrometry terms, electron configurations, ionisation energy concepts, and Period 3 melting point trends.

Isotopes

Elements with the same number of protons but a different number of neutrons.

Relative Atomic Mass ($A_r$)

The weighted mean mass of an atom of an element compared to $\frac{1}{12}\text{th}$ of the mass of an atom of carbon-12.

Relative Molecular Mass ($M_r$)

The mean mass of a molecule compared to $\frac{1}{12}\text{th}$ of the mass of an atom of carbon-12.

Relative Isotopic Mass

The mass of an atom of an isotope compared to $\frac{1}{12}\text{th}$ of the mass of an atom of carbon-12.

Periodicity

The repeating trends in the physical and chemical properties of elements as you move across the periods of the periodic table.

First Ionisation Energy

The amount of energy required to remove $1\,\text{mole}$ of electrons from $1\,\text{mole}$ of gaseous atoms to form $1\,\text{mole}$ of gaseous ions with a $+1$ charge.

General Equation for First Ionisation Energy

$$X_{(g)} \rightarrow X^+_{(g)} + e^-$$

Mass-to-Charge Ratio ($m/z$)

The mass of an isotope divided by its charge; since most ions have a $+1$ charge, this is effectively the same as the isotopic mass.

Order of Subshell Filling

Electrons fill from lowest to highest energy level in the order: $1s\, 2s\, 2p\, 3s\, 3p\, 4s\, 3d\, 4p$.

Subshell Electron Pairing Rule

Electrons fill up subshells individually before pairing up due to electron repulsion, and paired electrons in an orbital possess opposite spins.

Electron Configuration of Chromium ($\text{Cr}$) and Copper ($\text{Cu}$)

An electron from the $4s$ orbital moves into the $3d$ orbital to create a more stable half-full ($3d^5$ for $\text{Cr}$) or full ($3d^{10}$ for $\text{Cu}$) subshell.

Transition Metal Ion Formation

Transition metals lose electrons from the $4s$ orbital first before losing electrons from the $3d$ orbital.

Successive Ionisation

The endothermic removal of more than one electron from the same atom.

Factors Affecting Ionisation Energy

Atomic radius, nuclear charge (number of protons), electron shielding (number of shells), and the electrostatic forces of attraction between electrons and the nucleus.

Subshell Exceptions to Ionisation Energy Trends

Deviations occur because an outer-shell electron may occupy a higher energy subshell further from the nucleus, or because electron repulsion occurs in an orbital containing two paired electrons, requiring less energy to remove.

Melting Point Trend of Period 3 Metals ($\text{Na}, \text{Mg}, \text{Al}$)

Melting points generally increase due to stronger metallic bonds resulting from metal ions having increasing positive charges, an increased number of delocalised electrons, and smaller ionic radii.

Melting Point of Silicon ($\text{Si}$)

Silicon has the highest melting point in Period 3 because it has a giant covalent structure requiring large amounts of energy to overcome many strong covalent bonds.

Melting Points of Phosphorus ($\text{P}$) and Sulfur ($\text{S}$)

These non-metals have higher melting points than chlorine because they have larger simple molecular structures, resulting in larger London forces.

Melting Point of Chlorine ($\text{Cl}$)

Chlorine has a lower melting point than phosphorus and sulfur due to having a smaller simple molecular structure with weaker London forces.

Melting Point of Argon ($\text{Ar}$)

Argon has the lowest melting point in Period 3 because it exists as individual monoatomic atoms with the smallest London forces.