Transcript Camp 1

2
General, Organic, and
Biochemistry, 7e
Bettelheim,
Brown, and March
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2-1
2 Chapter 2
-1 0
10
m
Nu cleus (protons an d neu trons)
Space occupied by electrons
Proton
Atoms
Neu tron
10
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-1 5
m
2-2
2 Classification of Matter
Matter
anything that occupies
space and h as mas s
Pure su bstances
fixed comp osition; cannot
be further purified
Elements
cannot be
s ubdivided by
ch emical or
p hysical means
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Phys ically
separable into
Combine
chemically
Compound s
to form
elements united
in fixed ratios
Mixtures
a combin ation of tw o
or more p ure subs tances
Homogenous
matter
u niform
composition
th roughout
Heterogenou s
matter
nonu niform
composition
2-3
2 Classification of Matter
• Element: a substance (for example, carbon,
hydrogen, and iron) that consists of identical
atoms
• there are 114 known elements
• of these, 88 occur in nature; the others have been
made by chemists and physicists
• their symbols consist of one or two letters
• names are derived from a variety of sources: the
English name of the element, people important in
atomic science, geographic locations, planets,
mythological sources, etc.
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2-4
2 Classification of Matter
• Compound: a pure substance made up of two or
more elements in a fixed ratio by mass
• Formula of a compound: tells us the ratios of its
constituent elements and identifies each element
by its atomic symbol.
• NaCl: the ratio of sodium atoms to chlorine atoms in
sodium chloride is 1:1
• H2O: the ratio of hydrogen atoms to oxygen atoms in
water is 2:1
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2-5
2 A Water Molecule
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2-6
2 Classification of Matter
• Mixture: a combination of two or more pure
substances
• the substances may be present in any mass ratio
• each substance has a different set of physical
properties
• if we know the physical properties of the individual
components of the mixture, we can use appropriate
physical means to separate the mixture into its
component parts
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2-7
2 Dalton’s Atomic Theory
• All matter is composed of very tiny particles,
which Dalton called atoms
• All atoms of the same element have the same
chemical properties
• Compounds are formed by the chemical
combination of two or more of the same or
different kinds of atoms
• A molecule is a tightly bound combination of two
or more atoms that acts as a unit
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2-8
2 Evidence for Dalton’s Theory
• Law of Conservation of Mass
• mass can be neither created or destroyed
• if matter is made up of indestructible atoms, then any
chemical reaction just changes the attachments among
atoms, but does not destroy the atoms themselves
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2-9
2 Evidence for Dalton’s Theory
• Monatomic elements: consist of single atoms; for
example, helium (He) and neon (Ne)
• Diatomic elements: there are seven elements that
occur as diatomic molecules
• H2, N2, O2, F2, Cl2, Br2, and I2
• Polyatomic elements: some elements have three
or more elements per molecule
• O3, P4, S8
• diamond has millions of carbon atoms bonded together
to form one gigantic cluster
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2-10
2 Subatomic Particles
Su batomic
particle
Charge
Proton
Electron
N eutron
+1
-1
0
Mas s
(g)
Mass
(amu)
Mass (amu);
to one
sign ificant Location in
an atom
figure
1.6726 x 10-24 1.0073
1
9.1094 x 10-28 5.4858 x 10-4 0.0005
1.6749 x 10-24 1.0087
1
In the n ucleus
Outs id e the ucleus
In the n ucleus
• The unit of mass is the atomic mass unit (amu)
• one amu is defined as the mass of an atom of carbon
with 6 protons and 6 neutrons in its nucleus
1 amu = 1.6605 x 10-24 g
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2-11
2 A Typical Atom
• Protons and neutrons are found in the nucleus,
and electrons are found as a cloud outside the
10-1 0 m
nucleus
Nu cleus (protons an d neu trons)
Space occupied by electrons
Proton
Neu tron
10-1 5 m
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2-12
2 Mass and Atomic Numbers
•
Mass number: the sum of the number of protons plus neutrons
in the nucleus of an atom
• the mass of the electrons in an atom is so small compared
to that of its protons and neutrons that electrons are not
counted in determining mass number
• Atomic number: the number of protons in the nucleus of an
atom
Mass nu mb er (n umber of protons + neutrons)
Atomic n umber (n umber of protons )
•
12
6C
a carbon atom of this composition is referred to as carbon-12
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2-13
2 Isotopes
• Isotopes: atoms with the same number of protons
but a different number of neutrons
• carbon-12 has 6 protons and 6 neutrons; 126C
• carbon-13 has 6 protons and 7 neutrons; 136C
• carbon-14 has 6 protons and 8 neutrons; 146C
• Most elements found on Earth are mixtures of
isotopes
• chlorine is 75.77% chlorine-35 and 24.23% chlorine-37
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2-14
2 Atomic Weight
• Atomic weight: the weighted average of the
masses in amu of the isotopes of an element
found in nature
• example: chlorine is 75.77% chlorine-35 and 24.23%
chlorine-37
ch lorine-35
75.77 x 34.97 amu
100
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ch lorine-37
17
Cl
35.4527
+ 24.23 x 36.97 amu = 35.45 amu
100
atomic w eight in
the Periodic Tab le
is given to four
four decimal places
2-15
2 Mass and Size of an Atom
• Consider an atom of lead-208
• it has 82 protons, 82 electrons, and 126 neutrons
• it has a mass of 3.5 x 10-22 g
• it requires 1.3 x 1024 atoms to make 1 lb of lead-208
• the diameter of the nucleus is1.6 x 10-14 m
• the diameter of the atom is 3.5 x 10-10 m
• the density of the atom is 11.3 g/cm3
• the density of the nucleus is 1.8 x 1014 g/cm3
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2-16
2 Periodic Table
• Dmitri Mendeleev (1834-1907)
• arranged the known elements in order of increasing
atomic weight beginning with hydrogen
• he observed that when elements are arranged in this
manner, certain sets of properties recur periodically
• he then arranged elements with recurring sets of
properties in the same column (vertical row); Li, Na,
and K, for example, fall in the same column and start
new periods (horizontal rows)
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2-17
2 Periodic Table
• Fluorine, chlorine, bromine, and iodine fall in the
same column
9
F
7A
18.998
17
Cl
35.453
35
Br
79.904
53
I
126.90
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2-18
2 Classification of Elements
Metals
Metalloid s
N onmetals
1A
8A
H
2A
Li
Be
3A 4A 5A 6A 7A He
N a Mg
3B 4B
5B 6B 7B
K
Ca Sc
Ti
V
Rb
Sr Y
Zr N b Mo Te Ru Rh Pd Ag
Cs
Ba La
Hf Ta
Fr
Ra Ac Rf D b Sg Bh Hs Mt
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8B 8B 8B 1B
2B
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Cr Mn Fe Co N i Cu Zn Ga Ge As S e Br Kr
W
Re Os
Ir
Pt
-
Cd
Au Hg
-
-
In S n Sb Te
Tl Pb
-
Bi Po
I
Xe
At Rn
-
2-19
2 Classification of Elements
• Metals
• are solids (except for Hg), shiny, conductors of
electricity, ductile, and malleable
• form alloys (solutions of one metal dissolved in
another); brass, for example, is an alloy of copper and
zinc
• tend to give up electrons in their chemical reactions
• Nonmetals
• except for hydrogen (H), lie on the right side of the
Periodic Table
• except for graphite, do not conduct electricity
• tend to accept electrons in their chemical reactions
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2-20
2 Classification of Elements
• Metalloids
• six elements are classified as metalloids: boron,
silicon, germanium, arsenic, antimony, and tellurium
• they have some of the properties of metals and some
of nonmetals; for example, they are shiny like metals
but do not conduct electricity
• one of the metalloids, silicon, is a semiconductor; it
does not conduct electricity under certain applied
voltages, but becomes a conductor at higher applied
voltages
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2-21
2 Examples of Periodicity
• The halogens, Group 7A elements
7A
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9
F
18.998
17
Cl
35.453
35
Br
79.904
53
I
126.90
85
At
(210)
Melting Boiling
Point
Point
Elemen t (°C)
(°C)
Fluorine
Chlorine
Bromin e
Iodine
Astatine
-220
-101
-7
114
302
-188
-35
59
184
337
2-22
2 Examples of Periodicity
• The alkali metals, Group 1A elements
Melting Boilin g
Point
Point
Element
(°C)
(°C)
Lith iu m
180
Sodiu m
98
Potass iu m 63
Rubid iu m 39
Cesium
28
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1342
883
760
686
669
3
Li
6.941
11
Na
22.990
19
K
39.098
37
Rb
85.468
55
Cs
132.91
1A
2-23
2 Examples of Periodicity
• The noble gases, Group 8A elements
8A
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2
He
4.003
10
Ne
20.18
18
Ar
39.95
36
Kr
83.80
54
Xe
131.3
86
Rn
(222)
Melting Boiling
Poin t
Poin t
Element (°C)
(°C)
Helium
-272
-269
N eon
-249
-246
Argon
-189
-186
Kryp ton
-157
-152
Xenon
-112
-107
Rad on
-71
-62
2-24
2 Electron Configuration
• Electron configuration: the arrangement of
electrons in the extranuclear space
• The energy of electrons in an atom is quantized,
which means that an electron in an atom can
have only certain allowed energies
• Ground state: the electron configuration of lowest
energy
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2-25
2 Electron Configuration
• Electrons are distributed in shells about the
nucleus
nu cleus
4th s hell
.
3rd sh ell
2nd shell
1st s hell
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Relative
Electrons
en ergies
the s hell of electron s
S hell can hold in each s hell
h igher
4
32
3
2
1
18
8
2
low er
2-26
2 Electron Configuration
• Shells are subdivided into orbitals
Maximum nu mb er
of electrons s hell
S hell Orbitals contain ed in each shell
can hold
4 one 4s , three 4p, five 4d , and seven 4f orb itals 2 + 6 + 10 + 14 = 32
2 + 6 + 10 = 18
3 one 3s , three 3p, and five 3d orb itals
2+6= 8
2 one 2s and th ree 2p orbitals
1 one 1s orbital
2
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2-27
2 Electron Configuration
• Orbitals have definite shapes and orientations in
space
(insert Fig 2.11 of text)
(if it will not all fit on one screen, put part (a) on
one screen and part (b) on the next )
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2-28
2 Electron Configuration
• Electron configurations are governed by three
rules
• Rule 1: orbitals fill in the order of increasing
energy from lowest to highest
• elements in the first, second, and third periods fill in
the order 1s, 2s, 2p, 3s, and 3p
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2-29
2
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2-30
2 Electron Configuration
• Rule 2: each orbital can hold up to two electrons
with spins paired
• with four electrons, the 1s and 2s orbitals are filled and
are written 1s2 2s2
• with an additional six electrons, the three 2p orbitals
are filled and are written either 2px2 2py2 2pz2, or they
may be written 2p6
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2-31
2 Electron Configuration
• Spin pairing
means that
electrons spin in
opposite
directions
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1 A s pinnin g electron
generates a tiny
magn etic field
N
S
S
N
2 When their tin y magnetic
fields are align ed N -S, the
electron spin s are paired
2-32
2 Electron Configuration
• Rule 3: when there is a set of orbitals of equal
energy, one orbital becomes half filled before any
of them becomes completely filled
• example: after the 1s and 2s orbitals are filled, a 5th
electron is put into the 2px, a 6th into the 2py, and a 7th
into the 2pz. Only after each 2p orbital has one electron
is a second added to any 2p orbital.
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2-33
2 Electron Configuration
• Orbital box diagrams
• a box represents an orbital
• an arrow represents an electron
• a pair of arrows with heads in opposite directions
represents a pair of electrons with paired spins
• Example: carbon (atomic number 6)
Electron configuration
Exp anded : 1s2 2s2 2p x1 2py 1
1s
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2s
2px 2py 2pz
Con dens ed: 1s2 2s2 2p 2
2-34
2 Electron Configuration
• Noble gas notation
• the symbol of the noble gas immediately preceding the
particular atom indicates the electron configuration of
all filled shells
• Example: carbon (atomic number 6)
Orbital box diagram
Electron
Configuration
(conden sed)
2
2
1s 2s 2p
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2
N oble Gas
N otation
2
[He]2s 2p
2
2-35
2 Electron Configuration
• Valence shell: the outermost incomplete shell
• Valence electron: an electron in the valence shell
• Lewis dot structure:
• the symbol of the element represents the nucleus and
filled shells
• dots represent valence electrons
1A
H
2A
3A
4A
5A
6A
7A
8A
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
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2-36
2
Main group elemen ts;
s block (2 elemen ts )
1A
Main group elemen ts;
p block (6 elemen ts )
8A
3A 4A 5A 6A 7A 1s 1
2p
2
Tran sition elemen ts;
d block (10 elemen ts )
1 1s 2A
2s
2
Heliu m is
als o an s block
element
3
4
5
3s
5s
4d
4p
3
4
5
6
6s
5d
6p
6
7
7s
6d
7p
7
4s
3B 4B 5B 6B 7B 8B 8B 8B 1B 2B
3d
Inn er transition
elements; f block
(14 elemen ts)
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6
7
3p
5p
4f
5f
2-37
2 Electron Configuration
• Lewis dot structures for the Group 1A (alkali)
metals
N ob le
Lew is
Gas
dot
Element N otation Structure
Li
[He]2s1
Li•
Na
[N e]3s1
N a•
K
[A r]4s1
K•
Rb
[Kr]5s1
Rb•
Cs
[Xe]6s1
Cs •
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3
Li
6.941
11
Na
22.990
19
K
39.098
37
Rb
85.468
55
Cs
132.91
1A
2-38
2 Ionization Energy
• Ionization energy: the energy required to remove
the most loosely held electron from an atom in
the gaseous state
• example: when lithium loses one electron, it becomes a
lithium ion; it still has three protons in its nucleus, but
now only two electrons outside the nucleus
Li
+ en ergy
Lith iu m Ionization
energy
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Li+
+
eLithiu m
Electron
ion
2-39
2 Ionization Energy
• Ionization energy is a periodic property
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2-40
2 Ionization Energy
• Ionization energy is a periodic property
Ionization energy
• in general, it increases across a row; valence electrons
are in the same shell and subject to increasing
attraction as the number of protons in the nucleus
increases
• it increases going up a column; the valence electrons
are in lower principle energy levels, which are closer to
the nucleus and feel the nuclear charge more strongly
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2-41
2 Atoms
-1 0
10
m
Nu cleus (protons an d neu trons)
Space occupied by electrons
Proton
Neu tron
10
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-1 5
m
End
Chapter 2
2-42