Electrons & Energy Levels

The Atom Electrons are held at set distances from the nucleus in what we call shells

What keeps the electrons and shells spaced apart?

Energy levels in the electrons The energy held by an electron determines the orbital shell the electron will occupy

Increasing Energy Levels Highest energy level Lowest energy level

Packets of energy The best way to visualise the energy levels in electron orbits is to use the packet diagram. You can see the different energy levels of the electron orbits. They are like flight of stairs

Totally False So what we know The nucleus is a fixed ball of protons and neutrons in the centre of the atom. The electrons exist in a fixed shell around the nucleus, and stay in the shell due to their energy levels. Totally False

So it’s false, can you work out the truth The ______ of an atom consists of _______ and neutrons in the ____. They are constantly _______ round like footballs, this spinning action causes them to ____ and ____ over each other all of the time. The _______ exist in a fixed _____ around the nucleus, their position depends on the _____ level of the electron. They are constantly spinning around the nucleus in their _____, like planets around the sun. They can jump to a new higher ____ with an injection of energy and when they ___ energy they will drop into a lower shell. slip, shell, nucleus, shell, lose, slide, protons, orbits, constantly, energy, spinning, centre, electrons, lower

So it’s false, can you work out the truth The nucleus of an atom consists of protons and neutrons in the centre. They are constantly spinning round like footballs, this spinning action causes them to slip and slide over each other all of the time. The electrons exist in a fixed shell around the nucleus, their position depends on the energy level of the electron. They are constantly spinning around the nucleus in their orbits, like planets around the sun. They can jump to a new higher shell with an injection of energy and when they lose energy they will drop into a lower shell.

So how can an electron jump from one energy level to another What will it need to make the jump

So how can an electron jump from one energy level to another What will it need to make the jump To go to a higher energy level it needs an input of energy It drops down again as it loses the energy it gained.

An electromagnetic wave like light hits the electron: The energy it is carrying is passed to the electron this excites the electron and it jumps to a higher orbit

This input of high energy gives the electron so much energy it causes Gamma wave lots of energy This input of high energy gives the electron so much energy it causes the electron to jump completely off the atom

So with the electron gone. What will this mean to the overall charge on the atom?

This is Ionisation 1 more proton than electrons means that the atom now has an an overall charge of +1 The atom has been changed into a charged Ion This is Ionisation

So how do we know this? Sunday, 17 February 2019

The electron Thompson was studying the conductivity of gases in fluorescent tubes (neon) when he discovered the electron. An electric current flows through a low pressure gas when a high potential difference is applied between two electrodes The Cathode (negative electrode) gave off some invisible rays (Cathode rays) These rays could be deflected by electric fields  they were negatively charged particles called ELECTRONS. Low pressure gas Cathode Anode

Thermionic emission It is possible to produce electron emission from metals using low voltage between the anode and the cathode. The cathode has to be heated up to high temperatures (by a current flowing through a filament) Electrons will escape from the filament (Cathode) Electrons Cathode

Thermionic emission What would happen to the electrons if an anode (positive electrode) is placed near the cathode? The emitted electrons are attracted by the anode The anode exerts a force on each electron  the electrons gain K.E. Vacuum Cathode Anode

Electron deflection So, how did Thompson realised that the “cathode rays” are streams of negative particles? The cathode rays could be deflected by electric, or magnetic fields. Electrodes Draw the path of the electrons that go through the hole in the anode and between the positive and negative electrodes. Cathode Anode

Electron-volt We can measure the Ek (Kinetic Energy) of a charge which is accelerated across a potential difference using this formula: Kinetic Energy (J) = Charge (C) x Voltage (V) The charge of the electron (elementary charge) is e = 1.60 x 10-19 C So, we can define a new unit of energy, the ELECTRONVOLT: One electronvolt is the Kinetic Energy gained by an electron when it is accelerated through a potential difference of one volt.

Energy Levels

Neon Lamps But, why do fluorescent tubes emit light of different… C O L O U R S The gas that fills the tubes is different, so it emits different colour light when an electric current flows through it. And why do different gases emit different colours? To answer this question we must understand the nature of light and electromagnetic radiation, and the structure of the atom.

Neon Lamps Shine the light from a light bulb and different gas lamps through a prism. Then look at the spectra. What do you notice? What is the difference between the spectrum from the light bulb and the gas lamps? The light bulb gives a Continuous Spectrum. The gas lamps give a Line Spectrum. Each gas lamp gives different lines in their spectrum. Continuous Spectrum Line Spectrum

The Hydrogen Spectrum All elements have their own line spectrum emitted when an electric charge is passed through their vapour. For an hydrogen discharge tube this is the line spectrum we would obtain: 410 nm 434 nm 486 nm 656 nm 500 nm 600 nm 700 nm 400 nm The lines on the spectrum are the wavelengths of the light produced by the discharge through a hydrogen gas. What is this light made of?

The Photon: a massless particle We’ve always thought of light as a wave, because it behaves like a wave in many cases (e.g. refraction, reflection, diffraction…). However, Einstein discovered that in some instances light behaves like a particle. He called these “particles” PHOTONS. His observations extend to all electromagnetic waves. EM waves Oscillations of electric and magnetic fields Carry energy Higher frequency = higher the energy Photons Packets of EM waves Are packets of energy Energy depends on frequency What are they made of? What are they made of? Click on the questions in the boxes to reveal the answers! What do they carry? What do they carry? How is the energy carried affected? On what does their energy depend?

Photons emitted by filament lamp Representing a photon So, why does a photon behave like a particle? It is a packet of electromagnetic energy  gives the idea of an “item” occupying a certain space, and not a continuum like a wave propagating in space It travels in one direction only. So, a light bulb emits photons in all possible directions, with each photon travelling in one direction only. The energy of a single photon is “quantized” and measurable. So, if a single photon hits a surface, it is a bit like a ball hitting a wall. Photons emitted by filament lamp

Energy of a photon We can measure the energy of a photon using Einstein’s equation: h = 6.63 x 10-34 Js  Planck constant f = frequency of photon/electromagnetic radiation c = 3 x 108 m/s  speed of light in a vacuum l = wavelength of photon/electromagnetic radiation