P22_029.PDF

29. None of the reactions given include a beta decay, so the number of protons, the number of neutrons,

and the number of electrons are each conserved. Atomic numbers (numbers of protons and numbers of

electrons) and molar masses (combined numbers of protons and neutrons) can be found in Appendix F

of the text.

(a) 1 H has 1proton, 1electron, and 0 neutrons and 9 Be has 4 protons, 4 electrons, and 9

−

4=5

1= 4 neutrons. One of the

neutrons is freed in the reaction. X must be boron with a molar mass of 5 + 4 = 9 g / mol: 9 B.

(b) 12 C has 6 protons, 6 electrons, and 12 − 6=6neutronsand 1 H has 1proton, 1electron, and 0

neutrons, so X has 6 + 1= 7 protons, 6 + 1= 7 electrons, and 6 + 0 = 6 neutrons. It must be

nitrogen with a molar mass of 7 + 6 = 13 g / mol: 13 N.

−

7=8neutrons; 1 H has 1proton, 1electron, and 0 neutrons;

and 4 He has 2 protons, 2 electrons, and 4

−

2 = 2 neutrons; so X has 7 + 1

−

2=6protons,6

electrons, and 8 + 0

−

2 = 6 neutrons. It must be carbon with a molar mass of 6 + 6 = 12: 12 C.

neutrons, so X has 1+ 4 = 5 protons, 1+ 4 = 5 electrons, and 0 + 5