Download CHEMISTRY The Molecular Science

Chapter 2
Elements & Atoms
Dalton’s Atomic Theory
• An element is composed of tiny particles called atoms. All
atoms of a given element show the same chemical
properties.
• Atoms of different elements have different properties.
• Compounds are formed when atoms of two or more
elements combine. In a given compound, the relative
number of atoms of each kind are definite and constant.
• In an ordinary chemical reaction, no atom of any element
disappears or is changed into an atom of another element.
Chemical reactions involve changing the way in which the
atoms are joined together.
• The same elements can be combined to form different
compounds by combining the elements in different
proportion.
Dalton predicted
Law of Multiple Proportions
• 1g Cu + 0.252 g O  1.252 g CuO
• 1g Cu + 0.126 g O  1.126 g Cu2O
Rutherford’s Experiment
Rutherford’s Model of the Atom
• atom is composed mainly of vacant space
• all the positive charge and most of the mass
is in a small area called the nucleus
• electrons are in the electron cloud
surrounding the nucleus
Structure of the Atom
• Electron e• Proton p+
• Neutron n
Charge
-1
+1
0
Mass
0.0005
~1
~1
Relative size
of atom
and atomic
nucleus
Nucleus to atom
is like a pencil
dot to this
lecture hall
Scanning Tunneling Microscope
Atomic number, Z
• the number of protons in the nucleus
• the number of electrons in a neutral atom
• the integer on the periodic table for each
element
Mass Number, A
• the sum of the number of protons and
neutrons in the nucleus
• Approximately the mass of an atom
Nuclear Notation
X-A
e.g.
AX
e.g.
A
ZX
e.g.
C-12
12C
12
6C
An isotope has 35 electrons and 46 neutrons.
The identity of this isotope is best represented
as
1.
2.
20% 20% 20% 20% 20%
3.
4.
5.
1
2
3
4
5
Masses of Atoms
Carbon-12 Scale
Masses of the atoms are compared to the mass
of C-12 isotope having a mass of 12.0000
Mass Spectrometer
Atomic Masses and
Isotopic Abundances
natural atomic masses =
sum[(atomic mass of isotope)
 (fractional isotopic abundance)]
The average mass of the naturally occurring
isotopes
Cl 34.969x0.7577+36.966x0.2423=35.453amu
1.
2.
25% 25% 25% 25%
3.
4.
1
2
3
4
The Mole
• a unit of measurement, quantity of matter
present
• Avogadro’s Number
6.022  1023 particles per mole
• Latin for “pile”
• 1 C-12 atom has mass 12 amu
• 1 mole C-12 has mass 12 g
• Avogadro’s number converts between
moles and number of particles
• Molar mass converts between
moles and mass
• You are given a 1 carat diamond, how many
carbon atoms does it contain (1 carat=0.2 g)
• 1 carat C x 0.2 g/1carat = 0.2 g C
• 0.2 g C x 1 mol C/12.01 g C = 0.01665 mol C
• 0.01665 mol C x 6.022x1023 atoms C/1 mol C
=1.003x1022 C atoms
Development of Periodic Table
Mendeleev
• 1869 - Periodic Law
• allowed him to predict properties of
unknown elements
• the elements are arranged according to
increasing atomic weights
• Missing elements: 44, 68, 72, & 100 amu
Predicted Properties of Ekasilicon
Property
Ekasilicon Germanium
Atomic Weight 72
72.6
Color
gray
gray
Density, g/mL
5.5
5.36
Oxide
EsO2
GeO2
Chloride
EsCl4
GeCl4
Modern Periodic Table
Moseley, Henry Gwyn Jeffreys
1887–1915, English physicist.
• studied the relations among spectra of different elements.
• concluded that the atomic number is equal to the charge
on the nucleus based on the x-ray spectra emitted by the
element.
• explained discrepancies in Mendeleev’s Periodic Law.
Periodic Table of the Elements
IA
1
1
2
3
4
5
6
7
II A
III B
IV B
VB
VI B
VII B
VIII B
IB
II B
III A
IV A
VA
VI A
VII A
1
VIII A
2
H
H
He
1.008
1.008
3
4
5
6
7
8
9
4.0026
10
Li
Be
B
C
N
O
F
Ne
6.939
9.0122
10.811
12.011
14.007
15.999
18.998
20.183
11
12
13
14
15
16
17
18
Na
Mg
Al
Si
P
S
Cl
Ar
22.99
24.312
26.982
28.086
30.974
32.064
35.453
39.948
19
20
31
32
33
34
35
36
21
22
23
24
25
26
27
28
29
30
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
39.102
40.08
44.956
47.89
50.942
51.996
54.938
55.847
58.932
58.71
63.54
65.37
69.72
72.59
74.922
78.96
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
Br
79.909
53
Kr
83.8
54
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
85.468
87.62
88.906
91.224
92.906
95.94
* 98
101.07
102.91
106.42
107.9
112.41
114.82
118.71
121.75
127.61
126.9
131.29
55
56
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Cs
Ba
**La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.91
137.33
138.91
178.49
180.95
183.85
186.21
190.2
192.22
195.08
196.97
200.29
204.38
207.2
208.98
* 209
* 210
* 222
87
88
89
104
105
106
107
108
109
110
111
112
Fr
* 223
Ra ***Ac
226.03 227.03
Rf
Ha
Sg
Ns
Hs
Mt
* 261
* 262
* 263
* 262
* 265
* 268
* 269
* 272
* 277
58
59
60
61
62
63
64
65
* Designates that **Lanthanum
all isotopes are
Series
radioactive
*** Actinium
Series
114
Uun Uuu Unb
116
Uuq
118
Uuh
*285
*289
Based on symbols used by ACS
66
67
68
69
Uuo
*293
S.M.Condren 2001
70
71
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
140.12
140.91
144.24
* 145
150.36
151.96
157.25
158.93
162.51
164.93
167.26
168.93
173.04
174.97
90
91
92
93
94
95
96
97
98
99
100
101
102
103
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
232.04
231.04
238.03
237.05
* 244
* 243
* 247
* 247
* 251
* 252
* 257
* 258
* 259
* 260
Family Names
Group IA
alkali metals
Group IIA
alkaline earth metals
Group VIIA
halogens
Group VIIIA
noble gases
transition metals
inner transition metals
• lanthanum series rare earths
• actinium series
trans-uranium series
Diatomic Elements
• H2 N2 O2 F2 Cl2 Br2 I2 Memorize
• The “gens”
• Hydrogen, nitrogen, oxygen, halogens
• S8 and P4 No need to remember