AH Chemistry - Inorganic Chemistry - (a) - Electromagentic Radiation and Atomic Spectra

What can electromagentic radiation be described and characterised in?

Electromagentic radiation can be described in terms of waves and characterised in terms of wavelength and/or frequency.

What is the relationship between wavelength and frequency?

The relationship between wavelength and frequency is c=fλ.

What does c represent in c=fλ?

In c=fλ, c represents the speed of light.

What does f represent in c=fλ?

In c=fλ, f represents the frequency of the wave in s^-1.

What does λ represent in c=fλ?

In c=fλ, λ represents the wavelength in m.

What is wavelength?

Wavelength is the distance between wave crests, usually measured in metres or nanometres.

What is frequency?

Frequency is the rate of one wavecrest or the number of complete waves passing a fixed point per unit of time, usually one second.

What is the different types of radiation arranged in order of wavelength known as?

The different types of radiation arranged in order of wavelength is known as the electromagnetic spectrum.

What are the different types of radiation in order of increasing wavelength?

The different types of radiation in order of increasing wavelength are:

• Gamma rays

• Xrays

• Ultraviolet

• Visible light

• Infrared

• Microwaves

• Radiowaves

What are wavelengths of visible light normally expressed in?

Wavelengths of visible light are normally expressed in nanometres.

What can electromagnetic radiation be described as?

Electromagnetic radiation can be described as a wave, has a wavelength and frequency, and as a particle. Due to this, it is said to have a dual nature.

How does electromagnetic radiation behave when it is absorbed or emitted by matter?

When electromagnetic radiation is absorbed or emitted by matter, it behaves like a stream of particles. These particles are known as photons.

What does a photon carry?

A photon carries quantised energy proportional to the frequency of radiation.

What happens when a photon is absorbed or emitted?

When a photon is absorbed or emitted, energy is lost or gained by electrons within the substance.

What can photons in high frequency radiation do?

Photons in high frequency radiation can transfer greater amounts of energy than photons in low frequency radiation.

What is the energy associated with a single photon given by?

The energy associated with a single photon is given by:

E=hf or E=hc/λ

What is the energy associated with one mole of photons given by?

The energy associated with one mole of photons is given by:

E=Lhf or E=Lhc/λ. This gives the energy in Jmol^-1 .

What does h represent?

h represents Planck’s constant.

What does L represent?

L represents Avogadro’s constant..

Do we still need to know wavenumber?

What might electrons do when energy is transferred to atoms?

When energy is transferred to atoms, electrons within the atoms may be promoted to higher energy levels.

What must happen to allow for electrons to return to their original levels after being promoted to higher energy levels?

To allow for electrons to return to their original levels, energy must be lost from the atom. The atom emits a photon of light energy when an electron moves from a higher energy level to a lower energy level.

What does the light energy emitted by an atom produce and what does this provide direct evidence for?

The light energy emitted by an atom produces a spectrum that is made up of a series of lines at discrete (quantised) energy levels. This provides direct evidence for the existence of these energy levels.

How is absorption spectroscopy carried out and what does it produce?

In absorption spectroscopy, electromagnetic radiation is directed at an atomised sample. Radiation is absorbed as electrons are promoted to higher energy levels. An absorption spectrum is produced by measuring how the intensity of absorbed light varies with wavelength.

In emission spectroscopy, high temperatures are used to excite the electrons within atoms. As the electrons drop to lower energy levels photons are emitted. To allow the electrons to return to their original levels, energy must be lost from the atom. This energy is released in the form of a photon.

What is the spectrum of light emitted described as?

The spectrum of light emitted (atomic emission spectrum) is not continuous, but consists of a series of lines at discrete frequencies.

What does the spectrum of light not being continuous, but consisting of a series of lines at discrete frequencies provide direct evidence for?

The spectrum of light not being continuous, but consisting of a series of lines at discrete frequencies provides direct evidence for the existence of discrete (quantised) energy levels for electrons.

What does each element produce in its emission spectrum?

Each element produces a unique pattern of frequencies of radiation in its emission spectrum.

How is an emission spectrum of a sample produced?

An emission spectrum of a sample is produced by measuring the intensity of light emitted at different wavelengths.

In atomic spectroscopy, what is the concentration of an element within a sample related to?

In atomic spectroscopy, the concentration of an element within a sample is related to the intensity of light emitted or absorbed.