Topic 2 - Protons, Electrons, and Neutrons (p.113-120 and section 5.3)
I. Subatomic particles.
A. Protons
1. positive charge
2. located in the nucleus
3. always equal to the atomic number
4. same mass as a neutron
B. Electrons
1. negative charge
2. located in clouds surrounding the nucleus
3. equal to protons in an atom (neutral)
4. less than the number of protons in positive ions, greater than the number of protons in
negative ions
5. mass is 1/2000 compared to protons and neutrons
C. Neutrons
1. neutral charge
2. located in the nucleus
3. equal to the atomic mass minus the number of protons
4. same mass as a proton
II. Arrangement of electrons.
A. energy levels (shells or rings)
1. Maximum number of energy levels for an atom is 7.
2. Each energy level can hold a maximum of 2n2 electrons (maximum of 32), where n is
the number of the energy level.
B. sublevels (subshells)
1. Each energy level is divided into sublevels.
2. The number of sublevels is equal to n with a maximum of 4.
3. The sublevels are designated with the letters s, p, d, and f which indicate the shape of
the sublevel.
C. orbitals
1. A region of space within a sublevel with a high electron density.
2. s = 1 orbital, p = 3 orbitals, d = 5 orbitals, f = 7 orbitals
3. Each orbital can hold 2 electrons as long as they spin in opposite directions.
III. Representing electrons.
A. electron configurations
a. Sublevels are filled according to the diagonal rule
(1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p).
b. The number of electrons in each sublevel is written as an exponent.
(1s22s22p4 for oxygen)
c. The coefficients show the energy level the electrons are in.
d. The highest coefficient represents valence electrons.
B. noble gas method
a. Begin by choosing the noble gas (group 18) from the energy level above the atom.
(for bromine, we would choose argon)
b. Place the noble gas in brackets [Ar] and then proceed with the diagonal rule beginning
with the s-sublevel from the same energy level as the atom being represented (4s for
bromine).
c. The atomic number for the noble gas is the number of electrons represented by the
bracket notation (18 for argon).
d. Noble gas notation for bromine... [Ar]4s23d104p5
e. The noble gas method always shows all of the valence electrons.
C. electron configurations ending in d4 or d9 always borrow an s electron to become d 5 or d10 to
make them more stable.
Answers to practice problems:
1. B
2. D
3. E
4. C
5. E
6. D
7. D
8. C
9. B
10. C
1. _____ The element that contains 38 protons is...
A. sodium
B. strontium
C. uranium
D. bromine
E. bismuth
2. _____ The number of electrons, protons, and neutrons in argon-40 is...
A. 18 e, 18p, 40 n
B. 40 e, 40 p, 18 n
C. 18 e, 22 p, 18 n
D. 18 e, 18 p, 22 n
E. 40 e, 18 p, 22 n
3. _____ How many protons, neutrons, and electrons are in an atom of bromine?
A. 35 p, 45 n, 35 e
B. 35 p, 80 n, 35 e
C. 45 p, 35 n, 45 e
D. 80 p, 35 n, 80 e
E. cannot be determined without mass
4. _____ The chemical symbol for antimony is...
A. Sn
B. Ti
C. Sb
D. K
E. At
5. _____ Which of the following elements has the greatest number of p electrons?
A. C
B. Si
C. Fe
D. Cl
E. As
6. _____ The number of electrons, protons, and neutrons, respectively, in the 31P isotope are...
A. 15, 31, 15
B. 15, 15, 31
C. 15, 31, 16
D. 15, 15, 16
E. 31, 31, 16
7. _____ Which element has an electron configuration that does NOT follow the diagonal rule?
A. Fe
B. Mg
C. Al
D. Ag
E. Ni
8. _____ Which electron configuration is that of a noble gas?
A. 1s22s22p63s23p64s1
B. 1s22s22p63s23p4
C. 1s22s22p63s23p6
2 2
6 1
2 2
6 2
6 2
10
D. 1s 2s 2p 3s
E. 1s 2s 2p 3s 3p 4s 3d
9. _____ The f sublevel may contain a maximum of ____ electrons.
A. 2
B. 14
C. 6
D. 10
10. _____ The valence electrons are...
A. all electrons in an atom beyond the preceding noble gas.
B. all outermost electrons in a sublevel.
C. any s and p electrons in the highest energy level.
D. electrons in the last unfilled sublevel.
E. any electrons in a d sublevel.
E. 7