Download chemistry chapter 6 notes and more Study notes Chemistry in PDF only on Docsity!
UNIT 6: ELECTRONIC STRUCTURES & PERIODIC TRENDS
ELECTROMAGNETIC ENERGY
● Traveling Waves: move through a medium or space, transferring energy without transporting matter. Includes: ○ Amplitude/speed ( c ): ½ the distance between the peaks and troughs ( m/s ) ○ Wavelength (λ): The distance between two consecutive peaks or troughs ( meter, m ) ○ Frequency (v): The number of wave cycles per second, measured in hertz (Hz or s^-1) ○ Wavelength & frequency are inversely proportional
● Standing Waves: when 2 waves of the same frequency and amplitude travel in opposite directions and interfere. Includes: ○ Nodes: Points where destructive interference (dark regions coincide) results in no motion.
- # radial nodes = n - l - 1 (e.g. 1s = 0) ○ Antinodes: Points of maximum displacement due to constructive interference (brightest regions coincide). ○ Standing waves appear stationary, with energy oscillating in place.
Light comprises oscillating electric and magnetic fields that are perpendicular to each other , exhibits wave-like behavior, such as:
● Diffraction: Light bends around obstacles or spreads after passing through slits. ● Interference: Overlapping light waves can produce constructive or destructive interference patterns. ● Polarization: Light waves can oscillate in specific orientations.
Line vs. Continuous Emission Spectra
● Continuous Spectrum : Produced by objects like stars or incandescent bulbs, this spectrum contains all wavelengths of light without interruption , appearing as a smooth gradient of colors.
● Line Spectrum: Emitted by specific elements, it consists of discrete wavelengths corresponding to electron transitions within atoms. Each element has a unique line spectrum, like a "fingerprint," observable in emission or absorption experiments
BOHR’S MODEL
Most stable matter = lowest possible energy
Ground state: electron in its lowest energy orbit (n = 1)
Electron move from an orbit with lower n to higher n when atom absorbs energy as photon
Excited state: electron move to an orbit with higher n value (higher energy)
Electron falls from an orbit with a higher n to lower n when atoms emit energy as photon
Photons absorbed or emitted only have a wavelength that is discontinuous (hence the line spectra due to infrared portion on electromagnetic spectrum)
QUANTUM THEORY
Wave-Particle Duality: Extending the idea observed in light, matter (such as electrons) also exhibits both wave-like and particle-like behavior.
- Louis de Broglie Hypothesis : Particles of matter, like electrons, have a wavelength associated with their motion ( λ = h/p)
QUANTUM # SYMBOL VALUES DESCRIPTION
Principal n^ 1, 2, 3, 4, …. Energy level and size of orbital
Angular Momentum l^ 0 ≤ ℓ ≤ n –1 Shape of orbital (subshell)
Magnetic ml – ℓ ≤ ml ≤ ℓ Orientation of orbital
Spin ms +½ , –½ Electron spin direction
- Ions : ○ In transition metal ions, sss-electrons are often removed before d-electrons, contrary to the Aufbau filling order. ○ Example :
The periodic table is structured based on electron configurations:
- Element Groups : ○ Elements in the same group have similar outer electron configurations, which explains their chemical similarities.
- Block Classification : ○ The periodic table is divided into blocks based on the type of orbital being filled: ■ s-block : Groups 1 and 2 ■ p-block : Groups 13– ■ d-block : Transition metals ■ f-block : Lanthanides and actinides
TRENDS IN PERIODIC PROPERTIES
Atomic Radius: distance from the nucleus to the outermost electron of an atom.
● ⬇ ACROSS PERIOD, ⬆ DOWN A GROUP
■ As protons are added to the nucleus, the increased nuclear charge pulls
electrons closer, reducing the atomic radius. ■ New electron shells are added, increasing the distance between the outermost electron and the nucleus.
Ionization Energy (IE): energy required to remove one electron from a neutral atom in the gas phase.
● ⬇EX: A(g)→A+(g)+e ● ⬆ ACROSS PERIOD, ⬇ DOWN A GROUP ■ Nuclear charge increases, making it harder to remove an electron. ■ The outermost electrons are farther from the nucleus and experience more shielding, reducing the energy required for removal. ● EXCEPTION : Elements with half-filled or fully filled subshells have slightly higher ionization energies due to their stability. ○ Example : Oxygen (O) has a slightly lower IE than nitrogen (N) because N has a stable half-filled 2p2p2p subshell. ○ Beryllium (Be) has a higher IE 1 than boron (B)
Electronegativity: when an atom attracts shared electrons in a chemical bond.
● ⬆ ACROSS A PERIOD, ⬇ DOWN A GROUP
■ Atoms become smaller, and the increased nuclear charge attracts bonding electrons more strongly. ■ Larger atoms have weaker pull on shared electrons due to increased distance and electron shielding.
Electron Affinity: energy change that occurs when an atom in the gas phase gains an electron to form an anion:
● A(g)+e−→A−(g)
● A - EA = energy is released (favorable).
● A + EA = energy must be supplied (unfavorable).
● MORE ➖ ACROSS A PERIOD (increases in magnitude)
● LESS ➖ DOWN A GROUP (decreases in magnitude)
● EXCEPTIONS:
- Beryllium (BeBeBe) and magnesium (MgMgMg) have very low or positive EA.
- Nitrogen (NNN) has a less negative EA than oxygen (OOO).
- Noble gases are typically positive EA
