Chapter 2
Atoms and Elements
Dr. S. M. Condren
Dalton’s Atomic Theory
Postulates
• proposed in 1803
• know for first exam
Dr. S. M. Condren
Dalton’s Atomic Theory
Postulate 1
• An element is composed of tiny particles
called atoms.
• All atoms of a given element show the
same chemical properties.
Dr. S. M. Condren
Dalton’s Atomic Theory
Postulate 2
• Atoms of different elements have
different properties.
Dr. S. M. Condren
Dalton’s Atomic Theory
Postulate 3
• 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.
Dr. S. M. Condren
Dalton’s Atomic Theory
Postulate 4
• 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.
Dr. S. M. Condren
Structure of the Atom
Composed of:
• protons
• neutrons
• electrons
• protons
– found in nucleus
– relative charge of +1
– relative mass of 1.0073 amu
Dr. S. M. Condren
Structure of the Atom
Composed of:
• protons
• neutrons
• electrons
• neutrons
– found in nucleus
– neutral charge
– relative mass of 1.0087 amu
Dr. S. M. Condren
Structure of the Atom
Composed of:
• protons
• neutrons
• electrons
• electrons
– found in electron cloud
– relative charge of -1
– relative mass of 0.00055
amu
Dr. S. M. Condren
ATOM COMPOSITION
The atom is mostly
empty space
•protons and neutrons in
the nucleus.
•the number of electrons is equal to the
number of protons in a neutral atom.
•electrons in space around the nucleus.
•extremely small. One teaspoon of water has
3 times as many atoms as the Atlantic Ocean
has teaspoons of water.
Dr. S. M. Condren
Radioactivity
•
•
•
•
•
Alpha – helium-4 nucleus
Ra226  Rn222 + He4(a)
Beta – high energy electron
U239  Np239 + b-1
Gamma – energy resulting from transitions
from one nuclear energy level to another
• Ni60*  Ni60 + g
Dr. S. M. Condren
Penetrations of
Radioactive Emissions
Dr. S. M. Condren
Isotopes &
Their Uses
Heart scans with
radioactive
technetium-99.
99
43Tc
Emits gamma rays
Dr. S. M. Condren
The modern view of the atom was developed by
Ernest Rutherford (1871-1937).
Dr. S. M. Condren
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
Dr. S. M. Condren
Nucleus
If nucleus is 1”
The atom would be 1.5 miles in diameter
Dr. S. M. Condren
Ions
• Ion
– electrostatically charged atom or group of
atoms
• cations
– positive ions
• anions
– negative ions
• ionic compounds
– combination of cations and anions
– zero net charge
Dr. S. M. Condren
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
13
Al
26.981
Atomic number
Atom symbol
Atomic weight
Dr. S. M. Condren
Dr. S. M. Condren
Imaging
Dr. S. M. Condren
Which best represents the poles?
Dr. S. M. Condren
Quantum Corral
http://www.almaden.ibm.com/vis/stm/corral.html
Dr. S. M. Condren
Mass Number, A
• C atom with 6 protons and 6
neutrons is the mass standard
• = 12 atomic mass units (u)
• Mass Number (A)
= # protons + # neutrons
• A boron atom can have
A = 5 p + 5 n = 10 u
A
10
Z
5
B
Dr. S. M. Condren
Isotopes
• atoms of the same element which differ in
the number of neutrons in the nucleus
• designated by mass number
Dr. S. M. Condren
Isotopes of Hydrogen
H-1, 1H, protium
• 1 proton and no neutrons in nucleus
• only isotope of any element containing no
neutrons in the nucleus
• most common isotope of hydrogen
Dr. S. M. Condren
Isotopes of Hydrogen
H-2 or D, 2H, deuterium
• 1 proton and 1 neutron in nucleus
Dr. S. M. Condren
Isotopes of Hydrogen
H-3 or T, 3H, tritium
• 1 proton and 2 neutrons in nucleus
radioactive
electron antineutrino
Dr. S. M. Condren
The radioactive isotope 14C has how
many neutrons?
6, 8, other
Dr. S. M. Condren
The identity of an element is determined by the
number of which particle?
protons, neutrons, electrons
Dr. S. M. Condren
Mass Spectrometer
a simulation is available at
http://www.colby.edu/chemistry/OChem/DEMOS/MassSpec.html
Dr. S. M. Condren
Mass spectrum of C6H5Br
Dr. S. M. Condren
Atomic Masses and
Isotopic Abundances
natural atomic masses =
SUM[(atomic mass of isotope)
*(fractional isotopic abundance)]
Dr. S. M. Condren
Example: Chlorine has two isotopes, Cl-35 and Cl-37,
which have masses of 34.96885 and 36.96590 amu,
respectively. The natural atomic mass of chlorine is
35.453 amu. What are the percent abundances of the
two isotopes?
let x = fraction Cl-35 y = fraction Cl-37
x+y=1
y=1-x
(AW Cl-35)(fraction Cl-35) + (AW Cl-37)(fraction Cl-37) = 35.453
Thus: 34.96885*x + 36.96590*y = 35.453
34.96885*x + 36.96590*(1-x) = 35.453
x = 0.75757 <=> 75.757% Cl-35 Thus 24.243% Cl-37
Dr. S. M. Condren
Molar Mass-Molecular Weight
Sum
atomic masses
represented by formula
atomic masses => gaw
molar mass => MM
Dr. S. M. Condren
Example
What is the molar mass of ethanol, C2H5O1H1?
MM = 2(gaw)C + (5 + 1)(gaw)H + 1(gaw)O
= 2(12.011)C + 6(1.00794)H + 1(15.9994)O
= 24.022 + 6.04764 + 15.9994
= 46.069 g/mol
Significant figures rule for multiplication
Significant figures rule for addition
Sequence – multiplication then addition,
apply significant figure rules in proper sequence
Dr. S. M. Condren
The Mole
• a unit of measurement, quantity of matter
present
• Avogadro’s Number
6.022 x 1023 particles
• Latin for “pile”
Dr. S. M. Condren
One Mole of each Substance
Clockwise from top left:
1-Octanol, C8H17OH;
Mercury(II) iodide, HgI2;
Methanol, CH3OH; and
Sulfur, S8.
Dr. S. M. Condren
Example
How many moles of carbon dioxide
molecules are there in 10.00g of carbon
dioxide?
MM = 1(gaw)C + 2(gaw)O = 44.01 g/mol
#mol CO2 = (10.00g)
/ (1 mol/44.01g)
/
= 0.2272 mol
Dr. S. M. Condren
Mendeleev’s Periodic Table
Missing elements: 44, 68, 72, & 100 amu
Dr. S. M. Condren
Properties of Ekasilicon
Dr. S. M. Condren
Modern Periodic Table
the elements are arranged according to
increasing atomic numbers
Dr. S. M. Condren
Periodic
Table
of the
Periodic
Table
of the
Elements
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
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
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
79.909
53
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
113
114
115
116
Rf
Ha
Sg
Ns
Hs
Mt
* 261
* 262
* 263
* 262
* 265
* 268
Fr
* 223
Ra ***Ac
226.03 227.03
58
* Designates that **Lanthanum
all isotopes are
Series
radioactive
*** Actinium
Series
59
60
61
62
Uun Uuu Uub
* 269
* 272
63
64
* 277
65
Uut
118
Uuq Uup Uuh
Uuo
*284
*285
*288
*292
Based on symbols used by ACS
66
67
68
69
S.M.Condren 2006
*294
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
Dr. S. M. Condren
Organization of Periodic Table
• period - horizontal row
• group - vertical column
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
– actinium series
rare earths
trans-uranium series
Dr. S. M. Condren
Dr. S. M. Condren
ELEMENTS THAT EXIST
AS MOLECULES
Allotropes
Dr. S. M. Condrenof C
Dr. S. M. Condren
ELEMENTS THAT EXIST
AS DIATOMIC MOLECULES
Dr. S. M. Condren
ELEMENTS THAT EXIST
AS POLYATOMIC MOLECULES
S8 sulfur
molecules
White P4 and polymeric
red phosphorus
Dr. S. M. Condren