Light emission by Atoms Chemistry of Art Light emission by Atoms

colours & fires Stage 6 Chemistry Syllabus – Chemistry of Art (Option) Identify Na+, K+, Ca2+, Ba2+, Sr2+, and Cu2+ by their flame colour Perform first-hand investigations to observe the flame colour of Na+, K+, Ca2+, Ba2+, Sr2+, and Cu2+ (Demo only this lesson) Explain the flame colour in terms of electrons releasing energy as they move to a lower energy level Explain why excited atoms only emit certain frequencies of radiation Explain what is meant by n, the principal quantum number Identify that, as electrons return to lower energy levels, they emit quanta of energy which humans may detect as a specific colour

What’re those colours? The colours of all glowing substances have the same starting point. They come from atoms and molecules that have been excited to states of energy. Atoms in burning fireworks and stars have become excited by absorbing energy as heat; then convert that energy into coloured light which is emitted. The colours shown by an atom depend on how it’s electrons are configured. Thus, by investigating the colours an atoms of an element emit, we can determine its atomic structure and work out which element it is.

Activity 1

Activity 2 Specific metal ions are used in fireworks to show different colours Metal ions can be identified by the unique colours of their flames.

Activity 2 Specific metal ions are used in fireworks to show different colours Metal ions can be identified by the unique colours of their flames.

How are these colours emitted at an atomic level? Meetal Kumar

Atomic Emission SPECTRA in the electromagnetic spectrum Electromagnetic spectrum: range of all wavelengths of electromagnetic radiation Atomic Emission Spectra: Set of wavelengths of the electromagnetic spectrum emitted by excited electrons of an atom

What happens when white light passes through a prism? Instructions: Turn on the ray box Place the prism flat on the paper in front of the ray box so that the beam of light passes through it Turn off the lights Observe the beam of light as it enters and exits the prism What do u see?

What happens when white light passes through a prism? The light is separated and dispersed into the full visible spectrum

For example: Sunlight passes through a raindrop the light is dispersed into a visible rainbow

QUESTION What happens when we hold a prism in front of light emitted from these specific burning elements? Would we see the entire visible spectrum? A: Yes, we would see the entire visible spectrum B: No, we would see bands of light broken up C: No, we would see the colours refracting back into its white light form Answer:

For example, Na+ light is broken up into bands within the spectrum - Notice each element has a unique spectrum that is emitted, referred to as its ‘Fingerprint’ and allows us to determine which element is becoming excited

First lets look at the electron configuration of an atom Quantum numbers = energies of electrons in atoms or ‘shells’ They are like the ‘address’ of the electron No two electrons can occupy the same address N is called Principal energy level It is always a whole number

Question: If these energy levels or ‘shells’ are not occupied by electrons, are the shells still present? Yes or no? Answer: YES! The energy levels are always present

How do flame tests work

What causes the electron to become excited? 1) Electron begins in Ground State (electron in n=1) 2) Energy eg. heat is absorbed by electron 3) Electron bounces to higher energy level  enters Excited State (eg N=2,3,4) 4) Electron releases Photon (light energy)  moves back down to lower level energy N=1 – UV rays ( not visible) N=2 – Visible N=3+ - IR rays (not visible)

How do flame tests work

Using all this information allows us to observe colours emitted from fireworks or outer space for example and determine which elements are becoming excited and emitting that colour of light

Emission Spectra Pembe Hussain Objective: To explain the quantum concept. Objectives: To describe the Bohr model of the atom. To explain the relationship between energy levels in an atom and lines in an emission spectrum.

Mars Pale yellow patches Dark red patches

Chemical composition of Mars Pale yellow/white patches = hydrogen, helium, sulfur and sodium. Iron oxide and small traces of calcium Canyons = shadows

Jupiter Pale grey Orange

Jupiter’s composition Hydrogen, helium with ammonium Phosurphous, sulfur and hydrocarbons

Naturally white with slight blue tinge Sun when in space Naturally white with slight blue tinge

Sun when in space Helium and hydrogen

Colour of the sun when it is up during the day

No interfering wavelengths Sun when in space Helium and hydrogen No interfering wavelengths

SO WHAT ARE WE TALKING ABOUT?

The only electromagnetic waves detectable by human eyes Visible light The only electromagnetic waves detectable by human eyes

Put meetals picture here

It is from one “bump” to another. What is a wavelength? It is from one “bump” to another. The technical term for a “bump” is a crest 

Each colour has its own wavelength that sets it apart so we can see it

Within the visible light section, we have a break down of colours so that means: Visible light has its own spectrum`

Riddle: What does a fingerprint belonging to a human being, and the electron configuration of an element have in common???

So: each element has its own unique visible wavelength and colour They are both unique to the individual and element Different electron configurations Different electrons being excited @ different energy levels (n) different photons released Put flow chart/diagram here different wavelengths So: each element has its own unique visible wavelength and colour

Does an element emits only one colour? Question: Does an element emits only one colour? Yes and no. We see only one colour but, as electrons travel between different energy levels, they release different photons and wavelengths. We just see the most dominant wavelength. My dot point: Explain why excited atoms only emit certain frequencies of radiation Identify that as electrons return to lower energy levels, they emit quanta of energy which humans may detect as a specific colour

Potassium - K+ Flame colour is lilac YET: the potassium wavelength is a mixture of red @650 nm and blue @475 nm. From http://webmineral.com/help/FlameTest.shtml 4000 A o 5000 6000 7000 An atom actually emits all of the colours, but the only colour detected by the human eye is that wavelength most dominant in the emission spectrum

So…. It is the dominant wavelength Potassium when heated emits a lilac flame because: It is the dominant wavelength 4000 A o 5000 6000 7000

Each emission spectrum is unique to on particular element shows the electron configuration of a specific atom Each emission spectrum is unique to on particular element 4000 A o 5000 6000 7000 Why? Because it is like a finger print

Applications: Identify different chemicals in a solution/substance for art restoration and chemical analysis Fireworks Astronomers use telescopes with detection devices that are sensitive to wavelengths  Determine composition

Flame test colours Sodium, Na Calcium, Ca

Next lesson: You will perform a first-hand investigation into observing the flame colours. You will be given unknown solutions and from this lesson, you will be expected to indentify them.

FIREWORKS Fireworks

How do flame tests work