Overview
This lecture covers valence electrons, their importance in chemistry, the concept of orbitals and orbital shapes, and how the periodic table helps predict electron arrangement.
Valence and Core Electrons
- Valence electrons are the outermost electrons of an atom and are involved in chemical bonding.
- Core electrons are closer to the nucleus, strongly attracted, and largely inactive in chemical reactions.
- Chemistry mainly involves manipulating valence electrons.
Electron Position and Energy States
- Electrons are attracted to the nucleus and occupy the closest possible position, called the ground state.
- When energy is added, electrons can move farther out into an excited state.
- After excitation, electrons return to the ground state.
Orbitals vs. Orbits
- The Bohr model imagined electrons traveling in specific orbits, but this is inaccurate.
- Modern chemistry uses the concept of orbitals, which describe a region where there's a high probability of finding an electron.
- Electron clouds represent areas with a 90% chance of containing an electron.
Probability and Electron Clouds
- The probability of finding an electron is highest near the nucleus and decreases with distance.
- Electron location is described by probability distributions, not fixed paths.
- Orbital shapes are often drawn to enclose 90% of the electron probability.
Orbital Shapes
- "Orbital" replaces "orbit" to reflect the probabilistic nature of electron positions.
- Common orbital shapes include spherical (s), dumbbell (p), clover (d), and more complex (f) forms.
- Shape relates to the wave nature of electrons and their probability nodes.
Periodic Table and Orbital Blocks
- The periodic table is organized into blocks (s, p, d, f) that correspond to types of orbitals for valence electrons.
- The order of filling is s, p, d, then f blocks.
- Position on the table indicates the type of valence orbitals an element has.
Key Terms & Definitions
- Valence electron — An outer electron involved in chemical bonding.
- Core electron — An inner electron not usually involved in bonding.
- Ground state — The lowest energy arrangement of electrons, closest to the nucleus.
- Excited state — A higher energy, temporary electron arrangement further from the nucleus.
- Orbital — A region where there is a high probability of finding an electron.
- Electron cloud — The fuzzy region showing probable electron locations.
- Node — A region in an orbital where the probability of finding an electron is zero.
- s/p/d/f block — Sections of the periodic table corresponding to different types of orbitals.
Action Items / Next Steps
- Prepare for the next lesson on writing orbital diagrams and electron configurations to identify valence and core electrons.
- Review periodic table block organization (s, p, d, f).