Electrons in AtomsChapter 5

5.1 Wave Nature of Light Electromagnetic Radiation is a form of energy that

exhibits wavelike behavior as it travels through space.

Waves

Wavelength is the shortest distance between equivalent points on a continuous wave (λ)

Frequency is the number of waves that pass a given point per second, measured in Hz or s-1 (ν)

Amplitude is the wave’s height from origin to crest or trough

Waves All electromagnetic waves travel 3.00x108m/s Wavelength and frequency can be calculated

using the following equation:

c = λν The electromagnetic spectrum encompasses

all forms of radiation; long wavelength low frequency on one end and short wavelength high frequency on the other

Particle Nature of Light The wave model of light does not explain light’s interactions with matter. Planck concluded that matter can gain or lose energy in specific amounts

called quanta. He proposed that the energy of a quantum (minimum amount of energy that can be gained or lost by an atom) is related to the frequency of the emitted radiation:

h = 6.626x10-34 J•s = Planck’s constant

Einstein Einstein proposed that electromagnetic

radiation has both wavelike and particlelike natures.

Light has many wavelike characteristics AND can also be thought of as a stream of tiny particles called photons.

A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy.

5.2 Quantum Theory and the Atom Bohr Model

The lowest energy state of an atom is called its ground state.

When an atom gains energy, it is in an excited state.

Bohr related energy states to the motion of the electron within the atom.

Bohr’s Model and de Broglie’s Equation Bohr’s model explained hydrogen well, but

failed to explain the spectra of other elements. Electrons do NOT move around the nucleus in

circular orbits!

de Broglie predicted that all moving particles have wave characteristics (including electrons)

λ = h/νm

The Heisenberg Uncertainty Principle Heisenberg studied interactions between photons and

electrons and determined that it is fundamentally impossible to know precisely both the velocity and position of a particle at the same time.

Schrodinger Schrodinger derived an equation that treated

the hydrogen atom’s electron as a wave. This model applied equally well to atoms of

other elements! This atomic model became known as the

quantum mechanical model of the atom. Schrodingers equation results in a solution

known as a wave function, which is related to the probability of finding an electron within a particular region of space around the nucleus.

Orbitals Electrons occupy three-

dimensional regions of space called atomic orbitals.

These orbitals describe an electron’s probable location.

There are four types of orbitals, denoted by the letters s, p, d, and f.

5.3 Electron Configurations The arrangement of electrons in an atom is

called the atom’s electron configuration. Electron configurations are described by three

rules: The aufbau principle The Pauli exclusion principle Hund’s rule

Aufbau Principle All orbitals related to an energy sublevel are of equal

energy. (ex. All 2p orbitals are same energy) The energy levels within a principal energy level

have different energies. (ex. 2p higher than 2s) The sequence of energy sublevels within a principal

energy level is s, p, d, and f. Orbitals related to energy sublevels within one

principal energy level can overlap orbitals related to energy sublevels within another principal level. (ex. 4s is lower than 3d)

Aufbau Principle

Pauli Exclusion Principle A maximum of two electrons may occupy a single

atomic orbital, but only if the electrons have opposite spins.

Arrows are used to indicate electrons in an orbital.

Hund’s Rule Single electrons with the same spin must occupy

each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital.

Valence Electrons Electrons related to the atom’s highest

principle energy level are referred to as valence electrons.

Valence electrons determine the chemical properties of an element.

Electron Configurations Electron configurations

may be represented using orbital diagrams, electron configuration notation, and electron-dot structures.