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atomic structure

Matter & KMT, the nuclear atom, electron configuration, emission spectra, ionization energy.

matter & KMT · nuclear atom · emission & configuration · ionization energy

Matter & kinetic molecular theory

Classification. Element = one atom type; compound = fixed ratio of elements; mixture separable physically; a pure substance has a sharp mp/bp.

States. Solid: fixed shape/volume, particles vibrate. Liquid: fixed volume, particles flow. Gas: no fixed volume, random rapid motion.

Temperature. \(T\propto\overline{E_k}\), Kelvin scale; absolute zero = minimum random motion.

Changes of state. Melting/freezing, vaporization/condensation, sublimation/deposition. Plateau during a phase change: \(E\) changes, \(T\) constant; IMFs overcome/formed.

The nuclear atom

Notation. \(\ce{^{A}_{Z}X^{q}}\): protons \(=Z\), neutrons \(=A-Z\), electrons \(=Z-q\).

Isotopes. Same \(Z\), different \(N\); chemical properties nearly the same, physical/radioactive may differ.

Ions. Cation loses e⁻; anion gains e⁻.

Relative atomic mass. \(A_r=\sum(\text{fractional abundance}\times\text{isotopic mass})\).

Mass spectrum. x-axis \(m/z\), y-axis relative abundance; the molecular ion gives \(M_r\); the fragmentation pattern identifies the species.

Emission spectra & electron configuration

Emission. An excited e⁻ absorbs energy; a photon is emitted when the e⁻ falls: \(\Delta E=hf=hc/\lambda\). Line spectrum = quantized energy levels; convergence limit = ionization energy from the ground state.

Shells & orbitals. Shell \(n\) capacity \(2n^2\); sublevels \(s,p,d,f\) have 1, 3, 5, 7 orbitals; an orbital holds 2 e⁻ of opposite spin.

Filling order. \(1s\lt 2s\lt 2p\lt 3s\lt 3p\lt 4s\lt 3d\lt 4p\lt 5s\lt 4d\lt 5p\lt 6s\lt 4f\lt 5d\lt 6p\lt 7s\). Rules: Aufbau, Pauli, Hund.

Exceptions. Cr \([\mathrm{Ar}]\,3d^5 4s^1\), Cu \([\mathrm{Ar}]\,3d^{10} 4s^1\); remove \(4s\) before \(3d\) for transition-metal ions.

Blocks. s = groups 1–2 + He; p = groups 13–18; d = groups 3–12; f = lanthanoids/actinoids.

Ionization energy

Definition. \(\ce{X(g) -> X+(g) + e-}\). Successive IEs always increase; huge jump after the valence e⁻ are removed.

Trends. Across a period IE generally increases: \(Z_\mathrm{eff}\uparrow\), radius ↓. Down a group IE decreases: shielding/radius ↑.

Discontinuities. Group 13 lower than group 2 (p sublevel higher/less penetrating); group 16 lower than group 15 (paired e⁻ repulsion).