Download File - Garbally Chemistry

Chapter 3 Arrangement of electrons in the atom.
White light passed through a prism= Continuous spectrum
Hydrogen discharge tube=Line spectrum
Use spectrometer or hand held spectroscope.
Why is an emission spectrum produced? -Bohr theory
1. Electrons revolve around the nucleus in fixed paths called orbits.
2. Electron has a fixed amount of energy.
3. As long as the electron is in one energy level it neither loses nor gains energy.
4. When the electron absorbs energy- jumps from a lower to a higher energy
level.
5. Energy lost as it falls from a higher energy level to a lower energy level.
6. Definite amount of energy lost.
Light
emitted
h = Plank’s Constant
f = frequency
E2-E1=hf
7. Each definite amount of energy emitted gives rise to a line in the emission
spectrum.
8. Since only definite amounts of energy are emitted, therefore electrons can
occupy only definite energy levels.
Limitations of the Bohr Theory
It is mainly successful in explaining one electron system e.g. Hydrogen.
The Bohr Theory does account for the exhistence of sublevels.
The presence of atomic orbitals is also not accounted for.
Atomic Absorption Spectrometry.
Atoms can also absorb light.
If white light is passed through a gaseous sample of an element it is found that the
light that comes out has certain wavelengths missing. We can analyse and correspond
these to various elements.
Wave nature of the electron.
When the Bohr theory is applied to atoms with more than 1 electron it failed to
account for many of the lines in the emission spectrum of these atoms.
De Broglei-moving electrons had a wave motion associated with them.
Heisenberg’s Uncertainty Principle.-It is impossible to measure at the same time
both the velocity and position of electrons. This gives rise to the probability of finding
electrons in a particular position inside the atom. Gives rise to atomic orbitals.
An atomic orbital is a region in space where there is a high probability of finding an
electron.
Erwin Schroedinger.— used maths equations to work out probability of finding an
electron in any particular sublevel in an atom
S-orbital-----spherical in shape
P-orbital------ Dumbell in shape