# AP Physics 2: 2.2 Changes and Conservation Laws

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AP Physics 2: 2.2 Changes and Conservation Laws. Which of the following is not one of the possible energy levels for double-ionized lithium?

AP | AP Physics 2 |

AP Physics 2 | Changes and Conservation Laws |

Language | English Language |

Science Practice 2 | Using math appropriately |

Test Prep | AP Physics 2 |

### Transcript

right moving on okay, the ionization energy for double ionized lithium which

has the equal three protons is negative 13.6 electron volts which of the

following is not one of the possible energy levels for double ionized lithium

and here are the potential answers.... okay if you watch the last video the info on the [A couple watching protons spinning]

number of protons and ionization energy will sound familiar if you didn't watch

it well go check it out it's fantastic you'll laugh you'll cry and you'll just [People laughing]

learn a thing or two maybe and more importantly you'll have the math to

solve this question well in that last question we use Bohr's formula to find

the energy level of this atom the formula is e sub N equals Z squared over

N squared times the ground state energy level looks like that with Z at three [Bohr's equations on a board]

and a ground state energy level equaling the ionization energy negative thirteen

point six we know that the energy levels equal 9 over N squared times negative 13

point 6 well now we can just plug in numbers for n to see what works and what

doesn't if n equals 1 we find that the energy level equals negative 122.4

electron volts answer B) is a possible energy level so it's not the right

answer as we plug in more numbers will find that A) and C) are the n values of 2 [Answers A and C flashing]

and 5 respectively so those answers are out too but there's no whole number n

value that'd make D) a possible answer so that's the correct answer for this

question - N will always be a whole number after all there's no such thing

as energy level one and a half so it's not too hard to figure out the energy [Girl reading energy level book]

level as long as we know the atomic number and the ground state energy it

might take a little trial and error but we'll be able to do the math and get it [Boy stood by a slot machine]

right.. Sure, it might feel a little repetitive changing out the value for n

a few times but let's face it repetition is a fact of life in science and math so

as we were saying and here's your shmoop du jour brought to you by...[Man hitting ball with a paddle]