UNIT 1 - 1)electromagnetic radiation and atomic spectra Flashcards
What is electromagnetic radiation
Electromagnetic radiation is a form of energy
How do chemical reactions take place
- talk of atoms
- outer electrons
- Chemical reactions take place when the reacting atoms, molecules or ions collide with each other.
- Therefore the outer electrons are involved when different substances react together and we need to understand the electronic structure of atoms to explain the chemical properties of the elements
How is information about the electronic structure of atoms and molecules obtained ?
- Much of the information about the electronic structure of atoms and molecules is obtained using spectroscopic techniques based on different types of electromagnetic radiation.
What is the electromagnetic spectrum?
- The electromagnetic spectrum consists of many bands of electromagnetic radiation (visible light, microwaves, x-rays, radio signals are all forms of electromagnetic radiation) which differ in terms of energy(E), wavelength(λ )and frequency (f)
- Different types of electromagnetic radiation make up the electromagnetic spectrum
Forms of electromagnetic radiation
- Visible light, microwaves, x-rays, radio signals
- Visible light – the radiation that our eyes can detect, makes up only a small part of the electromagnetic spectrum
- Describe what visible light is
Visible light is the radiation our eyes can detect and makes up only small part of the electromagnetic spectrum. Visible light is split into seven different colours that have different wavelength and frequencies
How is electromagnetic radiation described
- how does it travel
- Electromagnetic radiation may be described in terms of waves therefore it can be specified by its wavelength and/or its frequency.
- can be described as waves that travel in a vacuum at a constant speed of 3 x 10^8 m s-1 with wavelengths between 10^-14 and 10^14 metres
What is wavelength
- units
- Wavelength is the distance between adjacent crests or high points of a wave
- it measured in metres however in chemistry the unit of wavelength most often used is the nanometre (nm)
- one nanometre is 10^-9 metres
So one metre is 1x10^9 nanometres - the symbol for wavelength is the Greek letter lambda (λ)
What is frequency
- frequency is the number of wavelengths that pass a fixed point in one second.
- the symbol for frequency is f
- frequency is measured as 1/time and so has units of s^-1, which is also known as the Hertz(Hz)
Velocity
- all types of electromagnetic radiation travel at the same velocity in a vacuum
- velocity is 3 x 10^8 m s-1
- this value is given the symbol c and is assumed to be the constant velocity of electromagnetic radiation anywhere
What is the relationship between frequency , velocity and wavelength
- f = c/λ Or c = fλ
c = velocity 3 x 10-8 ms-1 λ = wavelength m, (convert nm etc) f = frequency, Hz or s-1
Electromagnetic radiation can be ________ or _______.
Electromagnetic radiation can be absorbed or emitted
Examples of electromagnetic radiation being absorbed / emitted
- the absorption of ultraviolet radiation by our skin may cause sunburn.
- when we cook our food in a microwave oven , the absorption of microwave radiation by the water in the food causes the water molecules to vibrate , generating heat that cooks food.
What does electromagnetic radiation behave like when it is absorbed or emitted - and what is it called
- when electromagnetic radiation is absorbed or emitted by matter it behaves like more like a stream of particles than as a wave motion.
- these particles are called photons
What does it mean by electromagnetic radiation has a dual nature
- electromagnetic radiation can be considered both as a stream of photons and as waves with characteristic properties such as wavelength and frequency. Therefore we say that electromagnetic radiation has a dual nature : wave motion and streams of photons
What happens when a photon is emitted or absorbed
-High and low frequency
- when a photon is emitted or absorbed , energy is lost or gained by the electrons in the sample being studied
- photons which are at high frequencies transfer larger amounts of energy than photons in lower frequencies
Electromagnetic radiation that has a _____ __________ and ____ _________ , such as gamma rays , is at the ____ ______ end of the electromagnetic spectrum
- electromagnetic radiation that has a short wavelength and high frequency ,such as gamma rays, is at the high energy end of the electromagnetic spectrum
Radio waves and other radiation that has a _____ __________ and ___ _______ are at the ___ ______ end of the electromagnetic spectrum
- radio wave with a long wavelength and low frequency are at the low energy end of the electromagnetic spectrum
Energy increases as frequency ________ and wavelength _______
Energy increases as frequency increases and wavelength decreases
When a protein is absorbed or emitted, energy is gained or lost by electrons within the substance. the photons in high frequency radiation transfer greater amounts of energy than photons in low frequency radiation
What does this tell us
This tells us that the Energy (E) carried by a photon is related to its frequency
Relationship between energy and frequency
E = hf
Where H is Planck’s constant and has a value of 6.63 x10^-34 Js (this is joules , you would need to convert)
For Energy calculated in joules - in chemistry energy values are normally expressed as kJ mol-1 (kilo joules). How do you convert J to kJ
To convert from J to kJ The number value must be divide by 1000
However with the relationship E=Hf we can’t obtain the mol-1 in kJ mol-1 , how does the relationship change to obtain this
To obtain mol-1 in units of kJmol-1, the relationship changes to
: E =Lhf
- where L is Avogadro’s constant, having a value of 6.02 x 10^23
Summarise all these relationships in J, J mol-1 and kJ mol-1
Therefore :
E= hf gives the energy value in J
E= Lhf gives the energy value in J mol-1
E= Lhf/1000 gives the energy in kJmol-1
What doses the energy in units of kJmol-1 associate with
When the energy is in units of kJmol-1, this is the energy associated with one mole of photons
What is avogadros constant
- avogadros constant is the number of formula units in one mole of a substance and so the number of photons in one mole is 6.02 x 10^23 photons
Equation for relating energy in kJmol-1 to wavelength
As f = c/λ then : E = Lhc/1000 λ
What is spectroscopy
Spectroscopy is the study of how light and matter interact.
When electromagnetic energy interacts with matter there is a transfer of ______ from one type into another.
When electromagnetic energy interacts with matter there is a transfer of energy from one type into another.
Visible light is only a small part of the electromagnetic spectrum. A wider range would stretch from ______ ____ or to _____ and __ waves
- visible light is only a small part of the electromagnetic spectrum. A wider range would stretch from gamma rays to radio and TV waves
What happens when white light (such as the light from an ordinary light bulb) is passed through a prism
When white light (such as light from an ordinary light bulb) is passed through a prism , a rainbow effect is seen : a continuous range of wavelengths which shows up as colours is seen
- this is known as a continuous spectrum and includes all the colours in the visible part of the electromagnetic spectrum (from about 400-700nm)
What happens when the lights source is supplied by sodium chloride being heated in a Bunsen burner flame
- if the light source is supplied by sodium chloride being heated in a Bunsen burner flame, the spectrum turns out not to be a continuous spectrum but a series of lines of different wavelengths and thus different colours
What characteristic is the same for all photons of electromagnetic radiation
Velocity
Order of electromagnetic spectrum (types of radiation ) in order of increasing energy
Radio waves , microwaves , infrared , visible light ,ultraviolet , x rays , gamma rays
