Summary CHM2041 Chapter 8 Atomic Structures Fully Composed & the Best Scouring Guide

CHM2041 Chapter 8 Atomic Structures Fully Composed & the Best Scouring Guide Electromagnet Radiation - energy can be transformed between atoms and molecules in the form of light or electromagnetic dual nature of light - wave and particle transverse wave - perpendicular oscillating electric and magnetic fields wavelength (lambda) - distance traveled by wave in 1 complete oscillation; distance from the top (crest) of one wave to the top of the next wave; or successive troughs or nodes all visible and invisible wavelengths are called - ultraviolet radiation ROY G BIV Radiation - 380-750 nm; eyes detect this radiation 1 angstrom = - 1x10^-10 m = 1x10^-18 cm speed of propagation, c - distance traveled by ray per unit time in vacuum; all electromagnetic radiation travel at same rate (speed of light) = 2.998x10^8 Planck's Equation - -an object can gain or lose energy by absorbing or emitting radiant energy in quanta of specific frequency (v) -E=hv=h(c/lambda) -E= energy of a photon -h= planck's constant= 6.626x10^-34 Jxs/photon The Photoelectric Effect - -light can strike the surface of some metals causing electrons to be ejected (light: specific v or E) -demonstrates the particle nature of light Atomic line spectra and the Bohr atom - an emission spectrum is formed when an electric current passes through a gas in a vacuum tube (very low pressure) causing the gas to emit light -sometimes called a bright light spectrum Rydberg Equation - an empirical equation that predicts the wavelengths of the lines in the hydrogen spectrum - 1/lambda= R(1/n(1)^2 - 1/n(2)^2) -R= 1.097 x10^7 m^-1 -the n's refer to the numbers of the energy levels in the emission spectrum of hydrogen Bohr model of atom - -energies of e are quantized: e occupy certain orbits of specific energies -bohr's theory correctly explains the H emission spectrum and those of hydrogen-like ions (He+, Li2+, Be3+....etc.; 1e species) -the theory fails for all other elements (treats electron as particle) -the wave nature of the electron: deBroglie Energy is absorbed.... - an e in an atom jumps from ground level (n=1) to upper levels (n>1) -atom is now in an excited state (absorption spectrum) Energy is emitted.... - e jumps down from upper levels to lower levels; absorbed energy is then emitted as light; emission of photons (emission spectrum) Calculating Energy Difference, (Triangle)E, between 2 levels - (triangle)E= I E(final) - E(initial) I = R(H)(1/n(f)^2 - 1/n(i)^2) -R(H)= 2.18x10^-18 Wave Nature of Electron - -wavelike properties of matter -lambda= h/mv = h/p -h: planck's constant -m: mass of moving particle -v: velocity of particle p=mv: momentum Uncertainty Principle - it is impossible to determine both the position (x) and the momentum (p) of an electron simultaneously - e does not orbit the nucleus in defined paths (no orbits) Basic Postulates of Quantum Theory - 1. Atoms and molecules exist in certain energy states. Atoms and molecules change energy states by absorbing or emitting enough energy to bring it to a new energy state (the quantum condition) 2. atoms or molecules absorb or emit radiation (light) to change their energies. The V and lambda of light emitted or absorbed are related to the energy change by: E= hv = hc/lambda 3. allowed energy states of atoms and molecules can be described by quantum numbers - quantum numbers: solutions of the schrodinger, Heisenberg, and Dirac equations Schrodinger's equation - H (wavelength: looks like a trident) = E (wavelength) Four Quantum Numbers - describe energy states and orbitals of electrons in atoms (n, l, m, ms) Orbital - -region of space within which one can expect to find an electron (wave function of e in an atom) -no solid boundaries (cloud) -electron capacity: 2e per atomic orbital -space surrounding nucleus divided up into large volumes called shells -shells subdivided into smaller volumes called sub shells -orbitals located in sub shells -shells, sub shells, and orbitals described by 3 or 4 quantum numbers 1. Principle Quantum Number, n - - n = 1, 2, 3, 4.....infinity (indicates shells) -as n increases, so does size, energy and electron capacity -the electrons energy depends principally on n - E = -RHc/n(i)^2 = -2.179 x 10^-18 J/ n(i)^2 2. Angular Momentum Quantum, l - l = 0, 1, 2, 3, 4.....(n-1) always n > l l = s, p, d, f, g...... (sub shells) - l indicates the shape of the orbital - orbitals are the volume around the nucleus that the electrons occupy 90-95% of the time 3. Magnetic Quantum number, ml - -specifies spacial orientation ml = -l, (-l+1), (-l+2), ......0,......, (l-2), (l-1), +1 S orbital - n=1 l=0 ml=0 shape: sphere one type of s orbital p orbitals - n=2 l=1 ml=-1, 0, 1 one node in shape 3 types of p orbitals d orbitals - n=3 l=2 ml=-2, -1, 0, 1, 2 5 types of d orbitals f orbitals - n=4 l=3 ml=-3, -2, -1, 0, 1, 2, 3 7 types of f orbitals trident^2 - probability of finding the e at a point in space The probability density function,