Electromagnetic Radiation Wave Properties

1
Electromagnetic Radiation Wave Properties

• view radiant energy as propagating through space
  as vibrating electric and magnetic fields
  perpendicular to one another.
• velocity c
• 3.00 x 108 m/sec
• (speed of light)
• wavelength ????
• ??distance between peaks
• frequency ??????peaks/sec
• cps Hz sec-1
• amplitude height of wave

points where amplitude is zero node distance
between nodes ??/2 electromagnetic radiation
requires no medium
2
Relationship Between Wave Quantities
KNOW THIS!
3
(No Transcript)
4
Atomic Spectra

• when white light is passed through a prism, split
  into a continuous spectrum (ROYGBIV)
• a pure element, when heated, produces light which
  consists of a small number of narrow bands of
  color, separated by dark pattern is
  characteristic of each element
• lines spectral lines
• pattern atomic spectrum
• besides visible lines, there are also lines in
  other regions

5
Hydrogen Spectrum

• e.g. Hydrogen simplest atom
• ? 656, 486, 434, 410 397 nm what
  is the pattern?

6
Balmer Formula (Rydberg Equation)
The equation below, first proposed by
mathematician Balmer (mid-1800s), allows for the
calculation of all of the visible lines for
hydrogen.

• 1 RH 1 - 1
• ? 22 nl2
• RH Rydberg constant 1.097 x 107 m-1
• nl small gt 2 (e.g. 3, 4, 5 ...)

(
)

• The formula was later modified to account for
  lines in other regions
• 1 RH 1 - 1
• ? ns 2 nl 2
• NOTE although equation worked, no one at the
  time had any clue as to why they didnt even
  know why spectra had the narrow lines.

Lyman ns 1 UV Balmer ns 2
Vis Paschen ns 3 IR
(
)
7
(No Transcript)
8
Periodic Properties Atomic Size
For the Main Group Elements, atomic radii
generally increase going down the periodic
table, due to increase in shell number
(n). decrease going across the periodic table,
due to increased effective nuclear charge
(Zeff).
values in picometers 1 x 10-12 m
9
Periodic Properties Ionization Energies
Energy required to remove one electron from an
atom in the gas phase. A(g) A(g) e-
For the Main Group Elements, ionization energies
generally decrease going down the periodic
table, due to increase in shell number (n)
electron is farther from the nucleus. increase
going across the periodic table, due to
increased effective nuclear charge (Zeff).
10
Periodic Properties Electron Affinity
Energy of the process when one electron is
aquired by an atom in the gas phase. A(g)
e- A-(g)
By convention these values are negative
(exothermic), with a more negative value meaning
a larger electron affinity. Exceptions in trends
(C to N) due to electronic stabilities.
11
Periodic Properties Ionic Radii
Cations are always smaller than the original
neutral atom due to loss of electron density.
Anions are always larger than the original
neutral atom due to gain of electron density.
12
(No Transcript)