Chem 11.2-3 Atoms and Orbitals

Bohr’s Model

• correctly predicted the frequencies of lines in hydrogen’s atomic emission spectrum

• proposed quantized energy levels

• was not fully applicable to complex atoms

Color of light associated with the photon…

depends on the energy change that produces it

Ground state

Lowest allowable energy state of an atom

Excited state

When atoms gain energy

Energy States of Hydrogen (more of Bohr’s model)

• based around hydrogen atom:

  • electron moving around nucleus in circular orbits corresponding to the various allowed energy levels

• Energy levels in the hydrogen atom represented certain allowed circular orbits

• The smaller the electron’s orbit, the lower the atom’s energy state

• Assigned quantum number, n, to each orbit and calculated orbit’s radius

Hydrogen’s Line Spectrum (more Bohr!)

• Hydrogen atom is in the ground state, also called 1st energy level, does not radiate energy, and electron is in n=1 orbit

• When energy is added, the electron moves to a higher energy orbit (ex. n=2)

• In the excited state, an atom can move from different orbits causing the atom to emit a photon corresponding to the energy difference between the two orbits

  • These photons of certain energies (and therefore certain frequencies) create distinct colors

Quantum (Wave) Mechanical Model of the Atom

• proposed by de Broglie; accounted for Bohr’s idea of fixed energy levels

• Electron orbit have wave behavior/ wave-like motion

• Wavelength (upside down y) = h, Planck’s constant / (m, mass x v, velocity)

• All moving particles have wave characteristics

• Doesn’t describe electron’s path around nucleus (unlike bohr)

Heisenberg Uncertainty Principle

• Impossible to make any measurement without disturbing the object a little

• Fundamentally impossible to know precisely both the velocity and position of a particle at the same time

Schrödinger Wave Equation

• Derived an equation that treated the hydrogen atom’s electron as a wave

• Applied to atoms other than hydrogen

• Able to predict the probability of finding an electron in a given space around the nucleus

Atomic Orbital

• 3-D region around the nucleus that describes the electron’s probable location

• Density diagram represents likelihood of finding an electron at a particular point in the atom

Quantum mechanical model assigns four quantum numbers…

principal energy, angular momentum, magnetic and electron spin

Principal Quantum Number

n, indicates the main energy level of an electron in an atom

Angular Momentum Number

l, indicates the shape of the orbital and subshell in which the electron resides: s, p, d and f

+1/2 and -1/2 indicate…

the 2 fundamental spin states