Transcript CHEMICAL FOUNDATIONS: ELEMENTS AND ATOMS

CHEMICAL FOUNDATIONS:
ELEMENTS, ATOMS AND
IONS
Chapter 4
ANCIENT GREEKS’ VIEW
OF MATTER
About 400 B.C. , Aristotle thought all matter
was made of four “elements” :
• earth
• air
• fire
• water
ANCIENT GREEKS’ VIEW
OF MATTER
At about the same time another Greek
philosopher, Democritus, said that matter
was made of tiny, indivisible particles called
atoms.
Atomos is the Greek word for indivisible.
The Early History of Chemistry
- Before 16th Century
Alchemy: Attempts (scientific or otherwise) to
change cheap metals into gold--mercury, sulfur, &
antimony were discovered.
- 17th Century
Robert Boyle: First “chemist” to perform
quantitative experiments. Father of modern
chemistry--gave the modern definition to an
element.
The Early History of
Chemistry (continued)
- 18th Century
George Stahl: Phlogiston flows out of a burning
material.
Joseph Priestley: Discovers oxygen gas,
“dephlogisticated air.”
Law of Conservation of Mass
- Discovered by Antoine Lavoisier
- Mass is neither created nor destroyed
- Combustion involves oxygen, not
phlogiston
Other Fundamental Chemical Laws
Law of Definite Proportion (Law of
Constant Composition)
- A given compound always contains exactly
the same proportion of elements by mass.
- Carbon tetrachloride is always 1 atom
carbon per 4 atoms chlorine.
Figure 4.1: John
Dalton (1766-1844)
Dalton’s Atomic Theory (1808)
1 Each element is made up of tiny particles
called atoms.
2 The atoms of a given element are identical;
the atoms of different elements are
different in some fundamental way or
ways.
Dalton’s Atomic Theory
(continued)
3 Chemical compounds are formed when
atoms combine with each other. A given
compound always has the same relative
numbers and types of atoms.
4 Chemical reactions involve reorganization
of the atoms - changes in the way they are
bound together. The atoms themselves are
not changed in a chemical reaction.
Dalton’s Atomic Theory
Atoms are indivisible in a chemical process.
all atoms present at beginning are present at
the end
atoms are not created or destroyed, just
rearranged
atoms of one element cannot change into
atoms of another element
cannot turn Lead into Gold by a chemical
reaction
CHEMICAL ELEMENT
• a substance that cannot be further
decomposed into simpler substances by
chemical or physical means.
• consists of atoms that all have the same
atomic number.
• approximately 115 elements are known.
• 88 elements occur naturally.
• microscopic--single atom of an element.
• macroscopic--enough atoms to weigh on a
balance.
Table 4.1: Distribution (Mass Percent) of the
18 Most Abundant Elements in the Earth's
Crust, Oceans, and Atmosphere
CHEMICAL ELEMENTS
(continued)
What two elements make up nearly 75 % of
the solid earth?
oxygen--49.2 % & silicon--25.7%
What element is found in atmosphere, crust,
and oceans of the earth?
oxygen
Table 4.2: Abundance of elements in the
human body
Jons Jakob Berzelius
• developed the system of using letters to
stand for elements instead of symbols like a
crescent moon for Silver.
• 1st letter of symbol must be capitalized.
• 2nd letter (if there is one) is never
capitalized.
• Symbols are often from Greek, Latin, or
German.
Table 4.3: The names and symbols of the
most common elements
Chemical Symbols
Symbols commonly missed.
• A -- Al, Ar, As, Au, & Ag.
• B -- Ba, Bi, B, Br, & Be.
• C -- C, Ca, Cd, Cl, Cr, Co, Cs, & Cu.
• M -- Mg, Mn, & Mo.
• S -- S, Sb, Si, Sr, & Sn.
• Latin -- Fe, Au, Ag, Sb, Pb, Na, K, Hg, &
Cu.
• German -- W
Chemical Compound
• can be broken down into simpler substances
by chemical means.
• has a definite composition.
• energy changes accompany the formation of
a compound.
• Examples: CO, CO2,, NO, N2O, NO2, N2O3,
N2O5, SO2, SO3, As2S3, & As2S5.
Figure 4.16: (a) Sodium chloride (table salt) can
be decomposed to the elements sodium metal
and chlorine gas (b)
The Chemists’ Shorthand:
Formulas
Chemical Formula:
Symbols = types of atoms
Subscripts = relative numbers of atoms
CO2
Structural Formula:
Individual bonds are shown by lines.
O=C=O
Chemical Formulas
How many atoms of each element are found in
the following compounds?
• Ba(NO3)2
• (NH4)2SO4
• Ca(C2H3O2)2
• Ca3(PO4)2
Early Experiments to
Characterize the Atom
- J. J. Thomson - postulated the existence of
electrons using cathode ray tubes.
- William Thomson (Lord Kelvin) - proposed
the “plum pudding” model of the atom.
- Ernest Rutherford - explained the nuclear
atom, containing a dense nucleus with
electrons traveling around the nucleus at a
large distance.
Figure 4.7: Schematic of a cathode ray
tube
02_21
Applied
electric field
(+)
(-)
Metal
electrode
(+)
(-)
Metal
electrode
Cathode ray tube like the one used by J. J. Thomson to
determine the charge and relative mass of the electron.
Figure 4.8: A CRT being used to display
computer graphics
Thomson’s Plum Pudding Model
Electrons suspended in a positively charged electric
field
must have positive charge to balance negative
charge of electrons and make the atom neutral
mass of atom due to electrons
atom mostly “empty” space
compared size of electron to size of atom
Figure 4.3: The
plum pudding
model
02_23
Oil spray
Atomizer to
produce oil
droplets
X rays produce
charges on the
oil drops
(+)
Microscope
Electrically
charged plates
(-)
Oil drop apparatus used by Milliken to determine
the mass of the electron.
Figure 4.4: Ernest
Rutherford (1871-1937)
Figure 4.5: Rutherford’s experiment on particle bombardment of metal foil
Rutherford’s Results
Over 98% of the  particles went straight through
About 2% of the  particles went through but were
deflected by large angles
About 0.01% of the  particles bounced off the gold
foil
Figure 4.6: (a) The results that the metal foil
experiment would have yielded if the plum
pudding model had been correct; (b) Actual
results
Rutherford’s Nuclear Model
The atom contains a tiny dense center called
the nucleus
the volume is about 1/10 trillionth the
volume of the atom
The nucleus is essentially the entire mass of
the atom
The nucleus is positively charged
the amount of positive charge of the
nucleus balances the negative charge of
the electrons
The electrons move around in the empty space
of the atom surrounding the nucleus
The Modern Atom
The nucleus contains protons and neutrons
The nucleus is only about 10-13 cm in diameter
The electrons move outside the nucleus with an
average distance of about 10-8 cm
therefore the radius of the atom is about 105
times larger than the radius of the nucleus
Figure 4.9: A
nuclear atom
viewed in cross
section
The Modern View of Atomic
Structure
The atom contains:
- electrons: found in the electron shells, they have
a negative charge. (J.J. Thomson)
- protons: found in the nucleus, they have a
positive charge equal in magnitude to the
electron’s negative charge.
- neutrons: found in the nucleus, virtually same
mass as a proton but no charge. (James
Chadwick)
The Mass and Charge of the
Electron, Proton, and Neutron
Particle
Mass (kg)
31
Electron
9.11  10
Proton
1.67  1027
Neutron
1.67  10
27
Charge
1
1+
0
Subatomic Particles
Particle
Location
Mass #
Proton
Nucleus
1
Relative
Mass
1836
Neutron
Nucleus
1
1839
Electron
Electron
Shells
0
1
Isotopes
• Their discovery changed Dalton’s Atomic Theory
to say: “All atoms of the same element contain the
same number of protons and electrons, but atoms
of a given element may have different numbers of
neutrons.”
• Atomic number (Z) -- number of protons in the
nucleus
• Mass number (A) -- sum of the number of protons
and neutrons in the nucleus.
Isotopes
All isotopes of an element are chemically identical
undergo the exact same chemical reactions
Isotopes of an element have different masses
Isotopes are identified by their mass numbers
mass number = protons + neutrons
Figure 4.10: Two isotopes of sodium
The Chemists’ Shorthand:
Atomic Symbols
Mass number 
Atomic number 
39
K
19
 Element Symbol
Isotopes are “top heavy” -- mass
number is larger and on top.
Determining # of Subatomic
Particles
A=Z+N
How many protons, neutrons, and electrons
are found in the three isotopes of carbon,
carbon-12, carbon-13, and carbon-14?
6 protons, 6 electrons, and 6, 7, or 8 neutrons
Periodic Table
Elements classified by:
- properties
- atomic number
Groups (vertical)
1A = alkali metals
2A = alkaline earth metals
7A = halogens
8A = noble gases
Periods (horizontal)
The Modern Periodic Table
Main Group = Representative Elements
 “A”
columns
Transition Elements
 all
metals
Bottom rows = Inner Transition Elements = Rare
Earth Elements
 metals
 really
belong in Period 6 & 7
Important Groups - Halogens
Group 7A = Halogens
very reactive nonmetals
react with metals to form
ionic compounds
Fluorine = F2
 pale yellow gas
Chlorine = Cl2
 pale green gas
Bromine = Br2
 brown liquid that
has lots of brown
vapor over it
 Only other liquid
element at room
conditions is the
metal Hg
Iodine = I2
 lustrous, purple
solid
Important Groups
Noble Metals (Coinage Metals)
Ag, Au, Pt
all solids at room temperature
least reactive metals
found in nature uncombined with
other atoms
Noble Gases
• appear in nature in the uncombined state.
• all colorless gases at room temperature
• very non-reactive, practically inert eight electrons
in outer shell (octet) except helium which has two
(duet).
• monatomic gases (single atom molecules)
• six noble gases are:
He
Kr
Ne
Xe
Ar
Rn
Figure 4.13:
Argon gas
consists of a
collection of
separate argon
atoms
Figure 4.14: Gaseous nitrogen and oxygen
contain diatomic (two-atom) molecules
Diatomic Elemental Molecules
Elements that exist as diatomic (two atom) molecules
Remember: Count HOFBrINCl
H2
O2
F2
Br2
I2
N2
Cl2
Noble
gases
02_29
Alkaline
1 earth metals
Halogens
1A
1
Alkali metals
H
18
8A
2
13
14
15
16
17
2A
3A
4A
5A
6A
7A
2
He
3
4
5
6
7
8
9
10
Li
Be
B
C
N
O
F
Ne
11
12
13
14
15
16
17
18
Na
Mg
Al
Si
P
S
Cl
Ar
3
4
5
6
7
8
9
Transition metals
10
11
12
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
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
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
104
105
106
107
108
109
110
111
87
88
Fr
Ra
89
Ac†
Unq Unp Unh Uns Uno Une Uun Uuu
*Lanthanides
† Actinides
58
59
60
61
62
63
64
65
66
67
68
69
70
71
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
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
Periodic Table of the Elements
The Modern Periodic Table
Elements with similar chemical and physical
properties are in the same column
Columns are called Groups or Families
Rows are called Periods
Each period shows the pattern of properties
repeated in the next period
Why does the periodic table have 7 periods?
There are 7 electron shells.
Why does the periodic table have 8 groups?
Eight electrons is the maximum for an
outer electron shell.
Stair step or zig-zag line separating metals
from nonmetals.
Allotropes
• different forms of the same element
• the different physical properties arise from
the different arrangements of the atoms in
the solid
• the three allotropes of carbon are:
diamond
buckminsterfullerene
graphite
Figure 4.18a: The three solid elemental
(allotropes) forms of carbon
Figure 4.18b: The three
solid elemental
(allotropes) forms of
carbon
Figure 4.18c: The three solid elemental
(allotropes) forms of carbon
(c) Buckminsterfullerene
Physical Properties of Metals
Metals are:
1. efficient conductors of heat and electricity.
2. malleable (Can be hammered into thin
sheets).
3. ductile (Can be pulled into wires).
4. lustrous (shiny).
Examples are: Na, Cu, Au, Ag, & Fe.
Physical Properties of
Nonmetals
Nonmetals are:
1. nonconductors of heat and electricity
(insulators).
2. not malleable, but are brittle.
3. not ductile.
4. dull and without a luster.
Examples are: H, He, N, O, S, & P.
Metalloids
• substances with the properties of both
metals and nonmetals.
• also called semimetals
• Lie along the zigzag line between metals
and nonmetals
• The six metalloids are:
B, Si, Ge, As, Sb, and Te.
Electrical Nature of Matter
Most common pure substances are very poor
conductors of electricity
with the exception of metals and graphite
Water is a very poor electrical conductor
Electrical Nature of Matter
Some substances dissolve in water to form a
solution that conducts well - these are called
electrolytes.
When dissolved in water, electrolyte compounds
break up into component ions.
Solution Conductivity
In order for a substance to conduct electricity,
it must:
• contain ions.
• ions must be free to move (mobile).
Ions become mobile when the substance is:
• dissolved in water.
• melted (fused).
Figure 4.20: (a) Pure water does not conduct a
current; (b) Water containing a dissolved salt
conducts electricity
Ions
Ion: an atom or group of atoms with a net
positive or negative charge.
Ions are never formed by changing the
number of protons!
Cation: A positive ion
Mg2+, NH4+
Anion: A negative ion
Cl, SO42
The Chemists’ Shorthand:
Atomic Symbols
Mass number 
Atomic number 
39
1+  Ion charge
K
19
 Element Symbol
Atomic Structures of Ions
Metals form cations
For each positive charge the ion has 1 less
electron than the neutral atom
Na = 11 e-, Na+ = 10 eCa = 20 e-, Ca+2 = 18 e-
A=Z+N
35
17
35
17
Cl
0
1-
Cl
z
# protons # electrons # neutrons
17
17
17
18
17
17
18
18
Figure 4.12: The elements classified as
metals and nonmetals
NONMETALS
NONMETAL + n e- ------> Xnwhere n = 8 - Group #
C + 4 e- ---> C4- C4- carbide
N + 3 e- ---> N3- N3- nitride
O + 2 e- ---> O2- O2- oxide
F + e- ---> F1- F- fluoride
METALS
M ---> Mn+ + n ewhere n = periodic group
Na ---> Na+ + eMg ---> Mg2+ + 2 eAl ---> Al3+ + 3 eTransition metals --> M2+ or M3+
are common
Atomic Structures of Ions
Cations are named the same as the metal
sodium
Na  Na+ + 1esodium ion
calcium Ca  Ca+2 + 2ecalcium ion
The charge on a cation can be determined from the
Group number on the Periodic Table for Groups IA,
IIA, IIIA
 Group
1A  +1, Group 2A  +2, (Al, Ga, In)  +3
PREDICTING ION CHARGES
In general
metals (Mg) lose electrons ---> cations
nonmetals (F) gain electrons ---> anions
Charges on Common Ions
+1
+2
-4 -3 -2 -1
+3
Chemical Bonds
- the forces that hold two or more atoms
together to form a compound.
- the two types of chemical bonds are:
metal & nonmetal
1. Ionic bonds.
NaCl KI
2. Covalent bonds. two nonmetals
H2O CH4
Chemical Bonds
(continued)
Ionic Bonding: Force of attraction
between oppositely charged ions.
- Chemical compounds must have a net
charge of zero.
1. Both cations and anions must be present.
2. The number of cations and anions must
be such that the net charge is zero.
Writing Formulas for Ionic
Compounds
Charge must
equal zero for
each compound.
1
1-
Na Cl
2
1
2
1+ & 1- = 0
Ca F
2+ & 2- = 0
3
2
6+ & 6- = 0
23
Al S
COMPOUNDS FORMED
FROM IONS
CATION + ANION --->
COMPOUND
Na+ + Cl- --> NaCl
A neutral compound
requires equal
number of (+)
and (-) charges.
Figure 4.21a: The
arrangement of
sodium ions (Na+)
and chloride ions
(Cl-) in the ionic
compound sodium
chloride.
IONIC COMPOUNDS
ammonium chloride,
NH4Cl
NH4+
Cl-
Some Ionic Compounds
calcium fluoride
Ca2+ + 2 F- ---> CaF2
Name = calcium fluoride
Mg2+ + 2 NO3- ----> Mg(NO3)2
magnesium nitrate
3Fe2+ + 2PO43- ----> Fe3(PO4)2
iron(II) phosphate or ferrous
phosphate