Unit 1, Day 3 Suggested Problems
2.16 For the isotope !!𝐸 , where E is an element, y is the isotopes atomic number and gives the
number of protons, and x is the isotope’s mass number and is equal to the number of protons
and the number of neutrons.
!
!Li has 3 protons and 6 – 3 = 3 neutrons
!"
!"Al has 13 protons and 28 – 13 = 15 neutrons
!"
!"Al has 13 protons and 29 – 13 = 16 neutrons
!"
!"V has 23 protons and 50 – 23 = 27 neutrons
!!
!"Se has 34 protons and 77 – 34 = 43 neutrons
!"#
!!Ir has 77 protons and 193 – 77 = 116 neutrons
2.18 The value of Z gives the number of protons and the value of A gives the number of neutrons
and protons. The element’s identity is given by Z.
Z = 11, A = 23 is !"
!!Na
Z = 28, A = 64 is !"
!"Ni
Z = 50, A = 115 is !!"
!"Sn
!"
Z = 20, A = 42 is !"Ca
2.20 (a) Be has 4 protons, so adding 5 neutrons gives a mass number of 9
(b) Na has 11 protons, so adding 12 neutrons gives a mass number of 23
(c) Se has 34 protons, so adding 44 neutrons gives a mass number of 78
(3) Au has 79 protons, so adding 118 neutrons gives a mass number of 197
!.!!"×!"!
!
!
!
3.16 (a) 𝜈 = ! = !"#×!"!! ! = 6.57×10!" s !!
!
(b) 𝜆 = ! = !
!
!
!.!"×!"! !!!
!.!!"×!"!
!.!!"×!"!
×
!
!
3.26 (a) 𝜆 = ! = !.!×!"!" !!!
×
!"! !"
!
!"! !"
!
= 1.22×10! nm
= 400 nm
(b) 𝐸 = ℎ𝜈 = 6.626×10!!" Js 7.5×10!" s !! = 4.97×10!!" J
3.34 the energy of a single photon is 𝐸 =
!!
!
=
!.!"!×!"!!" !" !.!!"×!"! !/!
!"!×!"!! !
= 3.40×10!!" J
dividing the total energy by the energy per photon gives the number of photons; thus
!.!×!"!!" !
number of photons = !.!"×!"!!" !/!"#$#% = 118 photons
!
!.!"×!"!!" !
3.36 𝜈 = ! = !.!"!×!"!!" !/! = 8.84×10!" s !! ; any ν > 8.84!1014 s–1 is sufficient
3.37 𝐾𝐸 = ℎν − 𝐵𝐸 = (6.626×10−34 Js)(2.00×1015 s−1 ) − 5.86×10−19 J = 7.31×10−19 J
4.100 (a) cations will have more protons than electrons; thus: B, C, E, and F are cations
(b) anions will have more electrons than protons; thus: A and D are anions
(c) the elements are identified by the number of protons; thus
A has 7 protons and is nitrogen (N)
B has 20 protons and is calcium (Ca)
C has 48 protons and is cadmium (Cd)
D has 52 protons and is tellurium (Te)
E has 49 protons and is indium (In)
F has 41 protons and is niobium (Nb)