Saturday, 16 October 2010

Spectroscopy continued.

·         The Absorption Spectra looks at the frequencies absorbed by an element when light is passed through it

Light  à Gas à Less light

·         The Emission Spectra looks at the light given off when the element is exited
Excited element (heated up) à light is emitted. (Bohr’s theory)

·         Wave theory and particle theory are linked by Planck’s constant.

Bohr’s theory
Bohr stated that electrons start in their normal shell (Ground level or level 1: closest to the nucleus) but the atom still has outer shells (level 2, 3 …etc)

When the electron gains energy, the electron moves + shell, depending on the amount of energy (Which is known as a quantum: the energy required for an electron to jump up to the next level)

When the electron is in a higher level, it’s known to be in an ‘excited state’. However, the electron can’t stay in the excited state after the energy is given off (so it moves back to ground level)

Bohr:  As the electron jumps up a quantum, it absorbs light, which is why we get an absorption spectra. As it jumps back down, it emits the light it absorbed.

Bohr:  As you go towards outer shells, the layers get closer get closer to each another. Which is significant as it justifies why the frequency given off is different as the quantum gets smaller.

The energy of the photon is equal to the quantum. Knowing that, we can calculate frequency.

Both the photon value and the quantum are variables according to the level which the electron is at.

Petrol Components

Petrol is a mixture of:

Alkanes (Aliphatic/saturated) which are often in the three forms of
Straight chains (Typical hydrocarbons such as Ethane)
 Branched chains (Hydrocarbons with extra bonds such as 2-Methyl butane)
 Cyclic chains (Hydrocarbons in a circular structure such as Cyclohexane).

A few Alkenes such as the aromatic Benzene C6H6
(Aromatic Hydrocarbons: Hydrocarbons characterized by general alternating double and single bonds between carbons)

Which is increasing in amounts as a component in fuel over the years.
e.g. Ethanol and Ethers
(Ethers are 2 alkenes connected by an Oxygen [such as Ethoxyethane])

Petrol is/needs to be a blend of volatilities, and to burn well, i.e. not produce a lot of carbon monoxide.
Alcohols and ethers are known as oxygenates as they contain Oxygen.
Ethanol can be produced from fermentation, so it’s a biofuel.
Cons: Ethanol and ethers produce less energy per unit. (Low energy density) and that Ethanol is hydroscopic (Absorbs water) which may cause rust in vital components i.e. engine.