Chapter 7: Atomic Structure and Periodicity

electromagnetic radiation

properties of light

electromagnetic radiation

radiant energy that exhibits wavelike behavior and travels through space at the speed of light in a vacuum

Wavelength

λ) is the distance between two consecutive peaks or troughs in a wave

frequency

v) is defined as the number of waves (cycles) per second that pass a given point in space

relationship between wavelength and frequency

Note that the wave with the shortest wavelength has the highest frequency and the wave with the longest wavelength has the lowest frequency. This implies an inverse relationship between wavelength and frequency, that is, , or

change in energy for a system ΔE is represented by

ΔE= nhv,

n=an integer

h= plunk’s constant

v= frequency

emission spectrum of the hydrogen atom

Another important experiment was the study of the emission of light by excited hydrogen atoms. When a sample of hydrogen gas receives a high-energy spark, the molecules absorb energy, and some of the H-H bonds are broken. The resulting hydrogen atoms are excited; that is, they contain excess energy, which they release by emitting light of various wavelengths to produce what is called the emission spectrum of the hydrogen atom.

continuous spectrum

a spectrum that exhibits all the wavelengths of visible light.

line spectrum

a spectrum showing only certain discrete wavelengths.

significance of the line spectrum of hydrogen

indicates that only certain energies are allowed for the electron in the hydrogen atom. In other words, the energy of the electron in the hydrogen atom is quantized.

quantum model

Bohr proposed that the electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits. He calculated the radii for these allowed orbits by using the theories of classical physics and by making some new assumptions.

standing wave

a stationary wave as on a string of a musical instrument; in the wave mechanical model, the electron in the hydrogen atom is considered to be a standing wave.

wave function

a function of the coordinates of an electron’s position in three-dimensional space that describes the properties of the electron.

quantum (wave) mechanical model

a model for the hydrogen atom in which the electron is assumed to behave as a standing wave.

In a given atom no two electrons

can have the same set of four quantum numbers

Pauli exclusion principle

in a given atom no two electrons can have the same set of four quantum numbers.

an orbital can hold only two electrons, and they must have opposite spins.

aufbau principle

As protons are added one by one to the nucleus to build up the elements, electrons are similarly added to these hydrogen-like orbitals

Hund’s rule

The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli principle in a particular set of degenerate orbitals. By convention, the unpaired electrons are represented as having parallel spins (with spin “up”).

Ionization energy

the energy required to remove an electron from a gaseous atom or ion

Electron affinity

the energy change associated with the addition of an electron to a gaseous atom