Overview
This lecture reviews key concepts and practice questions from Chapter 6: Atomic Structure, including atomic composition, ions, isotopes, electron configurations, and quantum numbers.
Atomic Structure Basics
- Neutral atoms have equal numbers of protons (positive) and electrons (negative).
- The atomic number (Z) represents the number of protons in the atom.
- The mass number (A) equals the sum of protons and neutrons.
- Protons and neutrons are located in the compact nucleus with most atomic mass; electrons occupy most of the atom's volume.
Identifying Elements and Ions
- The atomic number identifies the element (e.g., Z = 24 is chromium, Cr).
- Ions have different numbers of electrons but the same number of protons.
- Isoelectronic species have the same number of electrons.
- Positive ions (cations) have lost electrons; for example, Ti4+ has 18 electrons.
Electron Configuration and Isotopes
- Electron configurations describe the arrangement of electrons in an atom.
- Only certain configurations are possible (e.g., no 2d orbital exists).
- Isotopes are atoms with the same number of protons but different numbers of neutrons (e.g., hydrogen and deuterium).
Calculations and Concepts
- Number of neutrons = mass number – atomic number (A – Z).
- Average atomic mass is calculated using weighted abundance.
- Electron configurations for transition metals may differ from predicted order (Aufbau exceptions).
- Paramagnetic species have unpaired electrons; all electrons paired indicates diamagnetic.
Quantum Numbers and Atomic Orbitals
- Four quantum numbers describe electron position: n (energy), l (subshell), m_l (orbital), m_s (spin).
- Each orbital holds up to two electrons with opposite spins.
- The maximum electrons in a d-orbital (like d_xy) is two.
- Ground-state configurations follow the principles of Hund's Rule and Pauli Exclusion.
Spectra & Energy Levels
- Energy levels in atoms are quantized, evidenced by atomic line spectra.
- Highest emission frequency results from the largest energy gap (e.g., transition from n=3 to n=1).
- Photoelectric effect demonstrates quantization of photons, not atomic energy levels.
Key Terms & Definitions
- Atomic Number (Z) — number of protons in an atom.
- Mass Number (A) — sum of protons and neutrons.
- Isoelectronic — species with the same number of electrons.
- Isotopes — atoms of the same element with different neutron numbers.
- Cation — positively charged ion (lost electrons).
- Paramagnetic — species with unpaired electrons; attracted by a magnetic field.
Action Items / Next Steps
- Review periodic table for atomic numbers and electron configurations.
- Practice determining electron configurations and identifying isoelectronic/ isotopic species.
- Prepare for homework on quantum numbers and atomic spectra.