Sub-Atomic Particles - Chemistry LibreTexts

Solutions and Explanations

1. There are 4 protons, 5 neutrons, and 4 electrons. This is a neutral beryllium atom.

2. Identify the subatomic particles present in the following:

• 146C
  • 6 protons, 8 neutrons, 6 electrons
    • There are 6 protons in accordance with the proton number in the subscript. There are 6 electrons because the atom is neutral. There are 8 neutrons because 14-6=8. 14 is the atomic mass number in the superscript.
• α
  • 2 protons, 2 neutrons, 0 electrons
    • This is an alpha particle which can also be written as 4He2+. There are two protons because the element is helium. There are no electrons because 2-2 = 0. There are 2 neutrons because 4-2=2.
• 35Cl-
  • 17 protons, 18 neutrons, 18 electrons
    • This is a chloride ion. According to the periodic table, there are 17 protons because the element is chlorine. There are 18 electrons due to the negative charge: 17-(-1) = 18. There are 18 neutrons because 35-17=18.
• β+
  • 0 protons, 0 neutrons, 0 electrons, 1 positron
    • This is a beta+ particle. It can also be written as e+. "e" represents an electron, but when it has as positive charge it is a positron.
• β-
  • 0 protons, 0 neutrons, 1 electron
    • This is a beta- particle, and can also be written as e-. This is a standard electron.
• 24Mg2+
  • 12 protons, 12 neutrons, 10 electrons
    • This is a magnesium Ion. There are 12 protons from the magnesium atom. There are 10 electrons because 12-2 = 10. There are 12 neutrons because 24-12 = 12.
• >60Co
  • 27 protons, 33 neutrons, 27 electrons
    • The cobalt atom has 27 protons as seen in the periodic table. There are also 27 electrons because the charge is 0. There are 33 neutrons because 60-27 = 33.
• 3H
  • 1 protons, 2 neutrons, 1 electrons
    • There is 1 proton because the element is hydrogen. There is 1 electron because the atom is neutral. There are 2 neutrons because 3-1 = 2.
• 40Ar
  • 18 protons, 22 neutrons, 18 electrons
    • There are 18 protons from the argon element. There 18 electrons because it is neutral, and 22 neutrons because 40 - 18 = 22.
• n
  • 0 protons, 1 neutrons, 0 electrons
    • This is a free neutron denoted by the lower case n.

3. Given the following, identify the subatomic particles present. (The periodic table is required to solve these problems)

• Charge +1, 3 protons, mass number 6.
  • 3 protons, 3 neutrons, 2 electrons
• Charge -2, 8 neutrons, mass number 17.
  • 9 protons, 8 neutrons, 7 electrons
• 26 protons, 20 neutrons.
  • 26 protons, 20 neutrons, 26 electrons
• 28 protons, mass number 62.
  • 28 protons, 34 neutrons, 28 electrons
• 5 electrons, mass number 10.
  • 5 protons, 5 neutrons, 5 electrons
• Charge -1, 18 electrons, mass number 36.
  • 17 protons, 19 neutrons, 18 electrons

4. Arrange the following lements in order of increasing (a) number of protons; (b) number of neutrons; (c) atomic mass.

a) Na, Mn, Fe, Co, Cu, Br

• Z=#protons;
• Na: z=11; Mn: Z=25, given; Fe: Z=26, given; Co: Z=27; Cu: Z=29; Br: Z=35, given

b) Na, Cu, Fe, Mn, Co, Br

• A=#protons+#neutrons, so #n=A-#protons(Z);
• Na: #n=23-11=12; Cu: #n=59-29=30; Fe: #n=56-26=30; Mn: #n=55-25=30; Co: #n=59-27=32; Br: #n=80-35=45

Note: Cu, Fe, Mn are all equal in their number of neutrons, which is 30.

c) Na, Mn, Fe, Co, Cu, Br

• Na: 22.9898 amu; Mn: 54.9380 amu; Fe: 55.845 amu; Co: 58.9332 amu; Cu: 63.546 amu; Br: 79.904

Note: This is the same order as the number of protons, because as Atomic Number(Z) increases so does Atomic Mass.

5. Fill in the rest of the table:

Atomic Number	Mass Number	Number of Protons	Number of Neutrons	Number of Electrons
2	4	2	2	2
11	23	11	12	11
15	31	15	16	15
37	85	37	48	37
53	127	53	74	53

Note: Atomic Number=Number of Protons=Number of Electrons and Mass Number=Number of Protons+Number of Neutrons