Download Atomic Structure

ATOMIC STRUCURE
The beginning:
1. Dalton’s Atomic Theory – 1808
2. Thomson’s Atomic Model – 1897
3. Rutherford’s Atomic Model –1911
4. Bohr’s Atomic Model –1913
5. Quantum Mechanical Model –
Useful Information:
Brief Description
Max Planck
Radiation emitted by heating solids to various temperatures. The
(1900)
energy emitted by atoms or molecules is always in whole number
multiples of energy of certain well-defined quantities. The word
Quanta or Quantum refers to the smallest quantity of energy that can
be emitted or absorbed in the form of electromagnetic radiation.
E=h, where h is Planck’s constant = 6.63 x 10-34 Js
Wave
Vibrating disturbance by which energy is transmitted. Speed of wave
depends on type of wave and the nature of medium through which the
wave is traveling.
James Maxwell
Electromagnetic wave has an electric and magnetic field component.
(1873)
Both have same wavelength and frequency.
Electromagnetic Range of energies, for example, ultraviolet radiation, infrared, x-rays,
Spectrum
radio waves, gamma rays, visible (ROYGBIV)
Electromagnetic All electromagnetic waves travel at the speed of light in a vacuum. 3.0
waves
x 108m/s
Albert Einstein
Proposed theory to explain the photoelectric effect. Einstein’s theory
(1905)
of light states that a beam of light behaves as a stream of particles
rather than wavelike. He called the stream of particles PHOTONS.
Later it was proposed that light behaves as either as waves or
particles. This property is also a characteristic of all matter.
Niels Bohr
Atomic structure was analogues to planetary system. Studied line
(1913)
spectra of hydrogen in gas phase. Line spectra due to the excitation
of electrons from lower energy level to a higher one. When the
electron falls to a lower energy level or ground state it emits a specific
amount of energy. The line spectra are not restricted to the visible
range but also extend into the UV and IR range. The energies
associated with electron motion in permitted orbits are fixed in value.
Therefore energies are QUANTIZED.
Louis De broglie If waves can behave like a stream of particles (photons) then so can an
(1924)
electron possess wave like properties. A particle in motion can be
treated as a wave and vise versa.
Brief Description
Davisson,
Experimentally proved that electrons possess wave-like properties.
Germer, G.P
Thomson
Werner
Heisenberg uncertainty principle states that it is impossible to know
Heisenberg
both the momentum (speed x mass) and position of a particle with
certainty.
Erwin
Schrodinger
(1926)
Quantum
Numbers
Principal
quantum number
Angular quantum
number
Magnetic
quantum number
Electron spin
quantum number
Electronic
configuration
Pauli Exclusion
principle
Hund’s rule
Aufbau principle
Ionization
energy
Formulated an equation that would describe the behaviour and energies
of submicroscopic particles in general. Used this equation to find the
probability of locating an electron in a given volume. This led to
quantum mechanics or wave mechanics model.
Describe the distribution of electron in an atom
Relates average distance of electron from nucleus to a particular
orbital. The bigger the number the larger the orbital. Energy level (n)
Sub shells. Orbital shapes (l). s, p, d, f, g, h…
Orientation of orbital in space (ml). The number of orientations can be
calculated using formula 2l+1
Orientation of electrons within a subshell (ms). Two electrons is the
same orbital will have opposite spins due to their opposite magnetic
fields.
Number of electrons distributed among various atomic orbitals.
No two electrons can have the same four quantum numbers. Therefore
electron spins must be opposite.
Most stable arrangement of electron in subshell is one with greatest
number of parallel spins.
Aufbau means building up in German. The process of building up the
ground state structure for each atom, in order of atomic number.
The energy needed to completely remove an electron from a ground
state gaseous atom.
Introduction to waves:
You are familiar with many types of radiant energy: visible light, UV-light, X-rays,
and gamma radiation. James Clerk Maxwell in 1856 proposed the existence of waves
which were related to both electricity and magnetism and called them Electromagnetic
waves.
Some waves require a medium to travel through, for example water waves and sound
waves. In a vacuum no sound waves will be heard. However,
ELECTROMAGNETIC WAVES, requires no medium of transmission. Can generate
electromagnetic waves by an accelerating electrically charged particles.
Wavelength
Amplitude
Frequency
Frequency: The number of waves that pass a given point in a unit time. Unit of
frequency 1 Hz = 1 s-1.
The velocity of a wave = wavelength x frequency
The velocity of electromagnetic waves through a vacuum is 3.0 x 108 ms-1 (3.0 x 10 8
m Hz). Since we will be concentrating on the nature of electromagnetic radiation then
the equation to be used is: Speed of light = frequency x wavelength