3.3 Collisions of electrons with atoms Flashcards

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1
Q

What is an ion?

A

» A charged atom

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2
Q

How is an ion formed?

A

» From an uncharged atom by adding or removing electrons from the atom

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3
Q

What does adding electrons make the atom?

A

» Negatively charged

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4
Q

What does removing the electrons do?

A

» Form a positive ion

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5
Q

What is ionization?

A

» A process of creating ions, when the electrons gain enough energy to be removed from the atom entirely to produce unbalance charges

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6
Q

What are the 3 radioactive radiations?

A

» Alpha
» Beta
» Gamma

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7
Q

When does Alpha, Beta , Gamma create ions?

A

» When they pass through substances and collide wit the atoms of the substance

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8
Q

What is the ionization energy of a gas atom?

A

» eV

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9
Q

What is the electron volt?

A

» Unit of energy equal to the work done when an electron is moved through a pd of 1V

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10
Q

What is the value of electron volt?

A

» 1.6 x 10^-19 J

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11
Q

What is excitiation?

A

» An electron in an energy level or an orbiting electron shell is given energy usually by collision to move to a higher energy level

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12
Q

When does excitation happen?

A

» At certain energies

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13
Q

What happens if the colliding electron does not have enough kinetic energy?

A

» It is deflected by the atom, with no overall loss of kinetic energy

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14
Q

What happens if a colliding electron loses all its kinetic energy when it causes excitation?

A

» The current due to the flow of electrons through the gas is reduced

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15
Q

When does ionisation occur?

A

» If the energy of the free electron is greater than the ionisation energy

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16
Q

What happens when an electron becomes de-excited?

A

» Will returns to its ground position and therefore release the energy it gained in the form of a proton

17
Q

Why is the excitation always less then the ionisation energy of the atom?

A

» Because the atomic electron is not removed completely from the atom when excitation occurs

18
Q

Why is the kinetic energy a maximum?

A

» Work function is the minimum amount of energy required to remove an electrons

19
Q

Explain why there is a current only if the frequency of the radiation is above a certain value?

A

» Energy of the photon is greater than the work function therefore electrons are emitted

20
Q

What happens to the current if you increase the intensity of the electromagnetic radiation?

A

» More photons per second are released
» Greater current

21
Q

What is the effect on the stopping potential if the frequency is increased?

A

» Energy of the photon is greater
» This would cause the stopping potential to increase
» As maximum kinetic energy of the electrons would be greater
» More work done is needed

22
Q

What is the ground state?

A

» When electrons are in their minimum energy state

23
Q

What are the differences between excitation and ionisation?

A

» Both receive the exact amount of energy required for the process to happen
» Excitation promotes an orbital electron to a higher energy level
» Whereas ionisation causes the electron to leave the atom completely

24
Q

Explain why only photons of a certain frequency cause excitation in a particular atom?

A

» There are discrete energy level
» Electrons need to absorb an exact amount of energy to excite
» Photons need to have a certain frequency to provide this energy
» All of the energy is absorbed when the electron excites

25
Q

What is kinetic energy equal to?

A

» E x v

26
Q

Why can a gas atom not absorb energy from a slow moving electron?

A

» Electron doesn’t have sufficient energy to excite or ionise the atom and so cannot be absorbed

27
Q

When happens when an electron collides with a gas atom and doesn’t cause it to ionise?

A

» Electron in the atom moves up a level

28
Q

Why is the mercury atom at low pressur?

A

» Vapor must not completely absorb the electrons

29
Q

Why do the emitted photons have specific wavelengths?

A

» Electromagnetic radiation is emitted when an electron falls
» From one fixed level to another fixed level
» Giving the photon a discrete amount of energy

30
Q

What does it mean by an excited atom?

A

» An electron in its lower energy state promotes to a higher energy level, causing the atom to gain energy