Physical Constants, Properties, Mathematical Calculations and Equations
Essay Preview: Physical Constants, Properties, Mathematical Calculations and Equations
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Emission
There are two significant effects of contamination by metal ions:
Salinity: When metal ion concentrations are too high and exceed safe limits. High salinity water is unsuitable for drinking or irrigation purposes.
Toxicity: Can occur even with extremely low concentrations of metal ions. These ions are often called heavy metal ions because their density are five times greater than that of water.
Atomic emission occurs when electrons are energetically promoted by the absorption of energy to an excited state from its ground state.
An emission spectrum is a graph with intensity of light plotted against wavelength (nm). All metals have a characteristic emission wavelength.
Consider the three possible electron transitions for a sodium ion. Ground state of Na is [Ne] 3s1. The valence electron can be promoter to any one of several excited states. It will usually jump to the next lowest energy level when heated in a flame. The electron configuration for a sodium ions 3s to 3p is represented as *[Ne] 3p1.
After a short period of time, the electron loses that energy by emitting it in the form of light. And emission spectrum can be recorded for the process.
To determine the energy emitted by the transition of an electron, we must know either wavelength (λ) or frequency (ν). The wavelength is related to the frequency and the speed of light (c) by the following equation with the speed of light constant 3.00 x 108m/s.
c = λ ν
The energy, E, of the emitted light is the product of Plancks constant, h = 6.63 x 10-34 J, and the frequency of light, ν.
E = h ν
When we combine equations 1 and 2, we can relate energy and wavelength.
ν = c/ λ
E = hc/ λ
Using our energy equation, we can calculate the energy of a photon of light emitted by an electron in a sodium atom that is moving from an excited to a ground state with a wavelength of 589 nm.
From there, we can calculate the energy emitted by 1 mole of Na atoms.
Absorption
Variables Defined:
P0 = the power of the light immediately after it passes through the first wall of the sample container.
P = the power of the light after it has passed the sample.
P1, P2 = The power of the light immediately before entering the sample container and immediately after exiting the container respectively.
Absorption spectroscopy is only interested in the