UNIT 1 - 1)electromagnetic radiation and atomic spectra

Question 1

What is electromagnetic radiation

Answer 1

Electromagnetic radiation is a form of energy

Question 2

How do chemical reactions take place

• talk of atoms
• outer electrons

Answer 2

• 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

Question 3

How is information about the electronic structure of atoms and molecules obtained ?

Answer 3

• Much of the information about the electronic structure of atoms and molecules is obtained using spectroscopic techniques based on different types of electromagnetic radiation.

Question 4

What is the electromagnetic spectrum?

Answer 4

• 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

Question 5

Forms of electromagnetic radiation

Answer 5

• 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

Question 6

• Describe what visible light is

Answer 6

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

Question 7

How is electromagnetic radiation described

- how does it travel

Answer 7

• 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

Question 8

What is wavelength

- units

Answer 8

• 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)

Question 9

What is frequency

Answer 9

• 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)

Question 10

Velocity

Answer 10

• 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

Question 11

What is the relationship between frequency , velocity and wavelength

Answer 11

• 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

Question 12

Electromagnetic radiation can be ________ or _______.

Answer 12

Electromagnetic radiation can be absorbed or emitted

Question 13

Examples of electromagnetic radiation being absorbed / emitted

Answer 13

• 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.

Question 14

What does electromagnetic radiation behave like when it is absorbed or emitted - and what is it called

Answer 14

• 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

Question 15

What does it mean by electromagnetic radiation has a dual nature

Answer 15

• 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

Question 16

What happens when a photon is emitted or absorbed

-High and low frequency

Answer 16

• 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

Question 17

Electromagnetic radiation that has a _____ __________ and ____ _________ , such as gamma rays , is at the ____ ______ end of the electromagnetic spectrum

Answer 17

• electromagnetic radiation that has a short wavelength and high frequency ,such as gamma rays, is at the high energy end of the electromagnetic spectrum

Question 18

Radio waves and other radiation that has a _____ __________ and ___ _______ are at the ___ ______ end of the electromagnetic spectrum

Answer 18

• radio wave with a long wavelength and low frequency are at the low energy end of the electromagnetic spectrum

Question 19

Energy increases as frequency ________ and wavelength _______

Answer 19

Energy increases as frequency increases and wavelength decreases

Question 20

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

Answer 20

This tells us that the Energy (E) carried by a photon is related to its frequency

Question 21

Relationship between energy and frequency

Answer 21

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)

Question 22

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

Answer 22

To convert from J to kJ The number value must be divide by 1000

Question 23

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

Answer 23

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

Question 24

Summarise all these relationships in J, J mol-1 and kJ mol-1

Answer 24

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

Question 25

What doses the energy in units of kJmol-1 associate with

Answer 25

When the energy is in units of kJmol-1, this is the energy associated with one mole of photons

Question 26

What is avogadros constant

Answer 26

• 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

Question 27

Equation for relating energy in kJmol-1 to wavelength

Answer 27

As f = c/λ then : E = Lhc/1000 λ

Question 28

What is spectroscopy

Answer 28

Spectroscopy is the study of how light and matter interact.

Question 29

When electromagnetic energy interacts with matter there is a transfer of ______ from one type into another.

Answer 29

When electromagnetic energy interacts with matter there is a transfer of energy from one type into another.

Question 30

Visible light is only a small part of the electromagnetic spectrum. A wider range would stretch from ______ ____ or to _____ and __ waves

Answer 30

• visible light is only a small part of the electromagnetic spectrum. A wider range would stretch from gamma rays to radio and TV waves

Question 31

What happens when white light (such as the light from an ordinary light bulb) is passed through a prism

Answer 31

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)

Question 32

What happens when the lights source is supplied by sodium chloride being heated in a Bunsen burner flame

Answer 32

• 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

Question 33

What characteristic is the same for all photons of electromagnetic radiation

Answer 33

Velocity

Question 34

Order of electromagnetic spectrum (types of radiation ) in order of increasing energy

Answer 34

Radio waves , microwaves , infrared , visible light ,ultraviolet , x rays , gamma rays