Chapter 2
Atoms & Elements
Dalton’s Atomic Theory
(beginning of 19th century)
• All matter is composed of tiny,
indivisible particles called atoms
• All atoms of a given element are
identical to each other and different
from those of other elements
• A chemical reaction merely involves
a change in the groupings of atoms
and not creation or destruction of
atoms (Law of Conservation of Mass)
• Compounds consist of atoms of
more than one element combined in
particular ratios (Law of Constant
Composition and Law of Multiple
Proportions)
Building up Atomic Structure
• Benjamin Franklin (1706-1790) discovered two
types of electricity, (+) and (-).
• Henri Becquerel discovered radioactivity on 1896.
Pierre and Marie Curie continued that work:
atoms disintegrate, i.e., they are divisible.
• John J. Thomson discovered the electron and
determined its charge/mass ratio (1896-97).
• Robert A. Millikan (1909) determined the charge
and mass of electron.
• Ernest Rutherford (1911-19) discovered the
proton.
• James Chadwick (1932) discovered the neutrons,
that are with the protons in the nucleus of atoms.
Atomic Structure
• subatomic particles
neutron: no charge, 1.0087 amu, n
proton: +1 charge, 1.0073 amu, p+
electron: –1 charge, 0.0005486 amu, e–
• n and p+ packed tightly into dense core
called nucleus
• e– distributed more diffusely in space
surrounding nucleus
e–
n
p+
e–
Actual size:
Radius of atom ~ 100 pm (10-10 m)
Radius of nucleus ~ 0.001 pm
Then, if radius of atom was ~ 100 m (a small football stadium),
the radius of the nucleus would be ~ 0.001 m = 1 mm
V  r3 Then, Vatom/Vnucleus  1015. Atom is 1015 times bigger
Atomic number and Mass number
• all atoms of a given element have the
same number of protons
• number of protons in an atom given by
the atomic number, Z
• neutral atoms have same number of
protons and electrons
• atoms gain or lose charge by gaining or
losing electrons only (not protons)
• total number of protons and neutrons
given by mass number, A. A = #p+ + #n
Symbol
mass number
charge
A
X
Z
atomic number
n
element symbol
Examples
Determine the numbers of electrons,
protons, and neutrons in each of the
following atoms.
40
Ar
18
40
Ar
18
Z = 18, therefore the atom has 18 p+
A = 40,
A = # of p+ + # of neutrons
Therefore, # neutrons = A − # p+
40 – 18 = 22 neutrons
Charge, n = 0, therefore # of e– = # p+ = 18
209
2+
Pb
82
• Z = 82, therefore 82 p+
• A = 209, therefore 209 p+ and n total
• # neutrons = A − # p+ = 209 – 82 = 127 n
• n = 2+,
• Therefore # e– = 82 p+ − 2 = 80 e– (lost 2 e–)
31
15
P
3–
31 3–
P
15
Z = 15, therefore 15 p+
31 3–
P
15
Z = 15, therefore 15 p+
A = 31, therefore 31 p+ and n total
31
15
P
3–
Z = 15, therefore 15 p+
A = 31, therefore 31 p+ and n total
31 – 15 = 16 n
31 3–
P
15
Z = 15, therefore 15 p+
A = 31, therefore 31 p+ and n total
31 – 15 = 16 n
n = 3 –, (gained 3 e–)
Therefore, # e− = 15 + 3 = 18 e−
Isotopes
• atoms (of same element) that have
the same number of protons but
different numbers of neutrons, i.e.,
different A
• may or may not have same number
of electrons
52
24X
55
24X
52
24X
55
24X
52
24X
52
20X
52
X
24
55
52
X
24
52
X
20
24
X
52 3+
50
24
24
X
X
Which of the
pairs of atoms
is(are)
isotope(s)?
Isotope abundance
A sample of naturally
occurring sulfur contains
several isotopes with the
following abundances
Isotope % abundance
32S
95.02
33S
0.75
32S, 33S, 34S, 36S
34S
4.21
16
16
16
16
36S
0.02
The %s have been determined experimentally.
# of atoms of a given isotope
% Abundance = ──────────────────────────── x 100
Total # of atoms of all isotopes of element
Mass Spectrometry is employed to
determine Isotopic Abundances
• mass spectrometer.
– Device generates ions that pass down an
evacuated path inside a magnet.
– Ions are separated based on their
charge/mass ratio. Mass is, then, calculated.
Atomic Weight
The atomic mass and Isotope Abundances are
determined by means of Mass Spectrometry.
Atomic mass of isotope carbon-12 is defined exactly 12
amu whereas all others of carbon and other elements
are referred to that and do not have integer values.
% abundance isotope 1
Atomic weight =  x (mass isotope 1)
100
% abundance isotope 2
+  x (mass isotope 2) + …
100
Example
Isotope % abundance
64 Zn
48.6
66Zn
27.9
67Zn
4.1
68Zn
18.8
70Zn
0.6
mass (amu)
63.9291
65.9260
66.9721
67.9249
69.9253
Example, contd.
%abund.i
Atomic weight of Zn = ∑   mi
100
A.W.= 0.486  63.9291 + 0.279  65.9260 + …
+ 0.041  66.9721 + 0.188  67.9249 + …
+ 0.006  69.9253 = 65.4 amu
# 25. Gallium has two naturally occurring isotopes,
69Ga and 71Ga, with masses of 68.9257 amu and
70.9249 amu, respectively. Calculate the % abundance
of the two isotopes of Ga. A W Ga = 69.723 (Per. table)
Let’s name p1 = % of 69Ga and p2 = % of 71Ga.
p1 + p2 = 100
then, p1 = 100 − p2
(1)
p1  68.9257 + p2  70.9249
AW = 69.723 = ────────────────────
then,
100
6972.3 = p168.9257 + p270.9249 Then, replace p1 by (1)
6972.3 = (100 − p2)  68.9257 + p2  70.9249
6972.3 = 6892.57 − p2  68.9257 + p2  70.9249
6972.3 − 6892.57 = p2  (70.9249 − 68.9257)
6972.3 − 6892.57
p2 = ─────────── = 39.88%
70.9249 − 68.9257
p1= 100 − p2 = 60.12%
Atoms and the Mole
A collection term states
a specific number of
items.
• 1 dozen donuts
= 12 donuts
• 1 ream of paper
= 500 sheets
• 1 case
= 24 cans
Atoms and the Mole
A mole is (a collection number) the amount of a
substance that contains
• the same number of particles (atoms,
molecules, ions, protons, electrons, etc.) as
there are carbon atoms in 12 g of carbon-12
isotope
• 1 mol = 6.022 x 1023 particles (Avogadro’s
number). Amadeo Avogadro
• The number is referred to the atomic mass
assigned to carbon-12 isotope.
Atoms and the Mole
1 mole of …
Number of particles
1 mole C
= 6.022 x 1023 C atoms
1 mole Na
= 6.022 x 1023 Na atoms
1 mole Au
= 6.022 x 1023 Au atoms
1 mole electrons = 6.022 x 1023 electrons
1 mole H2O
= 6.022 x 1023 H2O molecules
1 mole Na+
= 6.022 x 1023 Na+ ions
Molar Mass
The molar mass of any element is the mass in
grams of 6.022 x 1023 atoms of that element,
i.e., one mole of the element.
Molar mass is abbreviated M, has units of
grams per mole (g/mol), and is numerically
equal to the atomic weight of the element
(periodic table).
Molar mass of Na = 22.990 g/mol
Molar mass of Cl = 35.453 g/mol
Molar mass of O = 15.999 g/mol
Conversion factors
Avogadro’s number 6.022 x 1023 can be written as
equalities and conversion factors.
Equality:
1 mole = 6.022 x 1023 particles = molar mass (g)
Conversion Factors:
particles = atoms or molecules
6.022 x 1023 particles and
1 mole
1 mole
6.022 x 1023 particles
6.022 x 1023 particles
molar mass (g)
1 mole
molar mass (g)
and
and
molar mass (g)
6.022 x 1023 particles
molar mass (g)
1 mole
Converting moles ↔ mass
Moles to mass
g
moles x ──── = grams
1 mol
Mass to moles
1 mol
g x ────= moles
grams
The molar mass as conversion factors
What is the mass of silicon represented by
0.250 moles of this element? M of Si = 28.086
28.09 g
g/mol
0.250 moles x ────── = 7.02 g Si
1 mol
How many moles of manganese are 19.36 g of
that metal?
M of Mn = 54.938 g/mol
1 mol
19.36 g x ───── = 0.352384 = 0.3524 moles
54.938 g
4 SF
How many atoms of calcium are in 4.008 g of
that metal?
M of Ca = 40.08 g/mol
1 mol
6.022 x 1023 atoms
4.008 g x ────── x ─────────────
40.08 g
1 mol
= 6.022 x 1022 Ca atoms
The density of Au is 19.32 g/cm3. What is the
volume of a piece of gold that contains 2.6 x 1024
atoms? If the piece of metal is a square with a
thickness of 0.10 cm, what is the length (in cm) of
one side of the square? AW = 196.97 g/mol
196.97 g Au
2.6 x 1024 atoms Au x ──────────── = 850 g Au
6.022 x 1023 atoms
1 cm3
850 g Au x ──────── = 44 cm3 Au
19.32 g Au
side = l
V = th x A = th x l2
A = area =
thickness (th)
l2
l = SQRT (V/th) = SQRT (44 cm3 / 0.10 cm) = 21 cm
What is the average mass of one
germanium atom? M Ge = 72.59 g/mol
Here we have to divide the mass of a
mole by the number of atoms in that
mole.
1 mole Ge = 72.59 g = 6.02 x 1023 atoms
72.59 g Ge
1 mol Ge
g Ge
─────── x ───────────── = 1.205 x10-22 ─────
1 mol Ge
6.022 x1023 atoms Ge
atom Ge
0.0000000000000000000001205 g !!!!!!!
Periodic Table(*)
• a listing of the elements arranged according
to their chemical and physical properties
• elements are arranged according to similar
properties.
• Groups or families contain elements with
similar properties in vertical columns.
• periods are horizontal rows of elements.
Every period has a number (row) from 1
through 7.
(*) originally Mendeleev by atomic mass (1869),
later Moseley by increasing atomic number
(1913).
Periodic Table
Groups
• referred to by number or top element
• some have names:
The Representative Elements
• alkali metals - group 1A
• alkaline earth metals - group 2A
• noble gases - group 8A
• halogens - group 7A
• chalcogens - group 6A
• pnictogens - group 5A
Alkali Metals
Group 1A(1), the alkali metals, includes
lithium, sodium, potassium, rubidium,
cesium, and francium
Halogens
Group 7A(17)
the halogens,
includes
fluorine,
chlorine,
bromine, and
iodine.
Representative Elements
1
1A
1 1
1.008
3
2
2A
4
Li
Be
H
13
3A
5
6.941 9.012
11
12
Na
Mg
22. 99
19
24. 31
20
3
3B
21
K
Ca
Sc
39. 10
37
40. 08
38
44. 96
39
Rb
Sr
Y
85. 47
55
87. 62
56
88. 91
57
4
4B
22
5
5B
23
6
6B
24
7
7B
25
Ti
V Cr Cr
Mn
47. 88 50. 94
40
41
Zr
Nb
91. 22 92. 91
72
73
52. 00 9854. 94
42
43
8
8B
26
9
8B
27
10
8B
28
Fe
Co
Ni
55. 85
44
58. 93
45
58. 69
46
11
1B
29
12
2B
30
Cu
Zn
63. 55 65. 39
47
48
14
4A
6
15
5A
7
16
6A
8
17
7A
9
18
8A
2
He
4.003
10
B
C
N
O
F
Ne
10. 81
13
12. 01
14
14. 01
15
16. 00
16
19. 00
17
20. 18
18
Al
Si
P
S
Cl
Ar
26. 98
31
28. 09
32
30. 97
33
32. 07
34
35. 45
35
39. 95
36
Ga
Ge
As
Se
Br
Kr
69. 72
49
72. 59
50
74. 92
51
78. 96
52
79. 90
53
83. 80
54
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
95. 94
74
(98)
75
101.1
76
102.9
77
106.4
78
107.9
79
112.4
80
114.8
81
118.7
82
121.8
83
127.6
84
126.9
85
131.3
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.9
87
137.3
88
138.9
89
178.5
104
180.9
105
183.8
106
186.2
107
Uns
(262)
190.2
108
Uno
(265)
192.2
109
Une
(266)
195.1
197.0
200.6
204.4
207.2
209.0
(210)
(210)
(222)
71
Fr
Ra
Ac
Unq
Unp
Unh
(223)
(226)
(227)
(257)
(260)
(263)
58
59
60
61
62
63
64
65
66
67
68
69
70
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
140.1
90
140.9
91
144.2
92
(147)
93
150.4
94
152.0
95
157.3
96
158.9
97
162.5
98
164.9
99
167.3
100
168.9
101
173.0
102
175.0
103
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lw
232.0
(231)
238.0
(237)
(242)
(243)
(247)
(247)
(249)
(254)
(253)
(256)
(254)
(257)
Transition Elements
1
1A
1 1
1.008
3
2
2A
4
Li
Be
H
13
3A
5
6.941 9.012
11
12
Na
Mg
22. 99
19
24. 31
20
3
3B
21
K
Ca
Sc
39. 10
37
40. 08
38
44. 96
39
Rb
Sr
Y
85. 47
55
87. 62
56
88. 91
57
4
4B
22
5
5B
23
6
6B
24
7
7B
25
Ti
V Cr Cr
Mn
47. 88 50. 94
40
41
Zr
Nb
91. 22 92. 91
72
73
52. 00 9854. 94
42
43
8
8B
26
9
8B
27
10
8B
28
Fe
Co
Ni
55. 85
44
58. 93
45
58. 69
46
11
1B
29
12
2B
30
Cu
Zn
63. 55 65. 39
47
48
14
4A
6
15
5A
7
16
6A
8
17
7A
9
18
8A
2
He
4.003
10
B
C
N
O
F
Ne
10. 81
13
12. 01
14
14. 01
15
16. 00
16
19. 00
17
20. 18
18
Al
Si
P
S
Cl
Ar
26. 98
31
28. 09
32
30. 97
33
32. 07
34
35. 45
35
39. 95
36
Ga
Ge
As
Se
Br
Kr
69. 72
49
72. 59
50
74. 92
51
78. 96
52
79. 90
53
83. 80
54
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
95. 94
74
(98)
75
101.1
76
102.9
77
106.4
78
107.9
79
112.4
80
114.8
81
118.7
82
121.8
83
127.6
84
126.9
85
131.3
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.9
87
137.3
88
138.9
89
178.5
104
180.9
105
183.8
106
186.2
107
Uns
(262)
190.2
108
Uno
(265)
192.2
109
Une
(266)
195.1
197.0
200.6
204.4
207.2
209.0
(210)
(210)
(222)
71
Fr
Ra
Ac
Unq
Unp
Unh
(223)
(226)
(227)
(257)
(260)
(263)
58
59
60
61
62
63
64
65
66
67
68
69
70
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
140.1
90
140.9
91
144.2
92
(147)
93
150.4
94
152.0
95
157.3
96
158.9
97
162.5
98
164.9
99
167.3
100
168.9
101
173.0
102
175.0
103
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lw
232.0
(231)
238.0
(237)
(242)
(243)
(247)
(247)
(249)
(254)
(253)
(256)
(254)
(257)
Colors of solutions of
Transition Metal Compounds
Inner Transition Elements
1
1A
1 1
1.008
3
2
2A
4
Li
Be
H
13
3A
5
6.941 9.012
11
12
Na
Mg
22. 99
19
24. 31
20
3
3B
21
K
Ca
Sc
39. 10
37
40. 08
38
44. 96
39
Rb
Sr
Y
85. 47
55
87. 62
56
88. 91
57
4
4B
22
5
5B
23
6
6B
24
7
7B
25
Ti
V Cr Cr
Mn
47. 88 50. 94
40
41
Zr
Nb
91. 22 92. 91
72
73
52. 00 9854. 94
42
43
8
8B
26
9
8B
27
10
8B
28
Fe
Co
Ni
55. 85
44
58. 93
45
58. 69
46
11
1B
29
12
2B
30
Cu
Zn
63. 55 65. 39
47
48
14
4A
6
15
5A
7
16
6A
8
17
7A
9
18
8A
2
He
4.003
10
B
C
N
O
F
Ne
10. 81
13
12. 01
14
14. 01
15
16. 00
16
19. 00
17
20. 18
18
Al
Si
P
S
Cl
Ar
26. 98
31
28. 09
32
30. 97
33
32. 07
34
35. 45
35
39. 95
36
Ga
Ge
As
Se
Br
Kr
69. 72
49
72. 59
50
74. 92
51
78. 96
52
79. 90
53
83. 80
54
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
95. 94
74
(98)
75
101.1
76
102.9
77
106.4
78
107.9
79
112.4
80
114.8
81
118.7
82
121.8
83
127.6
84
126.9
85
131.3
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.9
87
137.3
88
138.9
89
178.5
104
180.9
105
183.8
106
186.2
107
Uns
(262)
190.2
108
Uno
(265)
192.2
109
Une
(266)
195.1
197.0
200.6
204.4
207.2
209.0
(210)
(210)
(222)
71
Fr
Ra
Ac
Unq
Unp
Unh
(223)
(226)
(227)
(257)
(260)
(263)
58
59
60
61
62
63
64
65
66
67
68
69
70
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
140.1
90
140.9
91
144.2
92
(147)
93
150.4
94
152.0
95
157.3
96
158.9
97
162.5
98
164.9
99
167.3
100
168.9
101
173.0
102
175.0
103
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lw
232.0
(231)
238.0
(237)
(242)
(243)
(247)
(247)
(249)
(254)
(253)
(256)
(254)
(257)
• rows = periods
• gradual transition in
properties from metallic to
nonmetallic moving from left
to right across a period
Metals
• Malleable: can be hammered or pressed
into new shapes (coins, rings, etc.)
• Ductile: can be pressed, beaten, or drawn
into shape when cold (wires, such as Cu)
• solid at room temperature (except for Hg)
• luster
• photoelectric effect (e– emission due to
light)
• thermionic effect (e– emission due to heat)
• readily lose electrons
• good thermal and electrical conductors
Nonmetals
•
•
•
•
•
•
•
solid, liquid, or gas
brittle if solid (fracture)
non-malleable, non-ductile
thermal and electrical insulators
do not exhibit photoelectric effect
do not exhibit thermionic effect
readily gain electrons
Metalloids (Semimetals)
• properties intermediate to those of
metals and nonmetals
• are located around the solid ladder
between metals and non-metals in
periodic table
• B, Si, Ge, As, Sb, Te, Po, At
Noble gases
• Are the least reactive elements
• Are gases, none-abundant on Earth,
but He is the second in the universe
after hydrogen
• Neon in advertising signs
• Some lasers are made of He, Ar, Kr
Learning Check
Identify each of the following elements as
1) metal
2) nonmetal
3) metalloid
A. sodium
B. chlorine
C. silicon
D. iron
E. carbon
F. antimony
____
____
____
____
____
____
Learning Check
Match the elements to the description.
A. Metals in Group 4A(14)
1) Sn, Pb
2) C, Si
3) C, Si, Ge, Sn
B. Nonmetals in Group 5A(15)
1) As, Sb, Bi
2) N, P
3) N, P, As, Sb
C. Metalloids in Group 4A(14)
1) C, Si, Ge,
2) Si, Ge 3) Si, Ge, Sn, Pb
Learning Check
The elements magnesium and calcium are in what
group?
a. alkali metals
b. alkaline earth metals
c. halogens
d. noble gases
Which elements are nonmetals?
a. sodium and potassium
b. magnesium and barium
c. boron and aluminum
d. carbon and bromine
Identify the period number for the row that ends in
argon.
a. Period 1 b. Period 2 c. Period 3
d.Period 4
Learning Check
Which statement is characteristic of metals?
A. They are shiny.
B. They are poor conductors of electricity.
C. They melt at high temperatures.
a. statement A only
b. statements A and B only
c. statements A, B, and C
d. statements A and C only
Which statement is false?
A. Potassium is an alkali metal.
B. Strontium is an alkaline earth metal.
C. Argon is a noble gas.
D. Zinc in a halogen.
Learning Check
What is the right order of increasing metallic
character for the elements Rb, F, P, Ga?
Rb < F < P < Ga
P < F < Rb < Ga
Ga< Rb < P < F
F < P < Ga < Rb
Learning Check
How many atoms are in 1.50 mol Na?
A.1.50 b. 9.03x1023 c. 3.00 d. 2.49x10-24
e. 345
6.0221023 atoms
1.50 mol  ──────────── = 9.03 x 1023 atoms
1 mol
How many moles of Ar in 5.22 x 1022 atoms of this
noble gas? a. 11.5
b. 0.0867 c. 1.15x1022
d. 8.67x1023
e. 3.14 x1046
1 mol
5.22 x 1022 atoms  ──────────── = 0.0867 mol
6.0221023 atoms
Learning Check
What is the mass (grams) of one atom of Na?
a. 22.99
1 mol Na
b. 0.04350 c. 3.818 x 1023 b. 2.619x1022
22.99 g
─────────── = 3.818 x 1023 g/atom
6.0221023 atoms