Download Chapter 2 ATOMS AND ELEMENTS

Chemistry and Chemical Reactivity 1
6th Edition
John C. Kotz
Paul M. Treichel
Gabriela C. Weaver
CHAPTER 2
Atoms and Elements
Lectures written by John Kotz
©2006
2006
Brooks/Cole
Thomson
©
Brooks/Cole
- Thomson
ATOMS AND ELEMENTS
© 2006 Brooks/Cole - Thomson
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Radioactivity
• One of the pieces of evidence for
the fact that atoms are made of
smaller particles came from the
work of Marie Curie (18761934).
• She discovered radioactivity,
the spontaneous disintegration
of some elements into smaller
pieces.
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Types of Radioactive Emissions
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Types of Radioactive Emissions
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ATOMIC COMPOSITION
• Protons
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic
mass units (u)
• Electrons
–
negative electrical charge
– relative mass = 0.0005 u
• Neutrons
no electrical charge
– mass = 1.009 u
–
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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.
•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.
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The modern view of the atom was developed
by Ernest Rutherford of New
Zealand (1871-1937).
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Ernest Rutherford
Canterbury
University in
Christchurch, NZ
Rutherford laboratory
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The modern view of the atom was developed by
Ernest Rutherford (1871-1937).
Screen 2.9
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Atomic Number, Z
All atoms of the same element
have the same number of
protons in the nucleus, Z
13
Al
26.981
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Atomic number
Atom symbol
Atomic weight
Atomic Weight
• This tells us the mass of one atom of
an element relative to one atom of
another element.
• OR — the mass of 1000 atoms of one
relative to 1000 atoms of another.
• For example, an O atom is
approximately 16 times heavier than an
H atom.
• Define one element as the standard
against which all others are measured
• Standard = carbon
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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
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A
10
Z
5
B
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Boron in Death Valley
•Death Valley has been a major source of
borax and other boron-containing minerals.
•Borax was transported out of Death Valley
in wagons pulled by teams of 20 mules.
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Isotopes
• Atoms of the same element (same Z)
but different mass number (A).
• Boron-10 has 5 p and 5 n: 105B
• Boron-11 has 5 p and 6 n: 115B
11B
10B
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Hydrogen Isotopes
Hydrogen has _____ isotopes
1 H
1
1 proton and 0
neutrons, protium
2 H
1
1 proton and 1
neutron, deuterium
3 H
1
1 proton and 2
neutrons, tritium
radioactive
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Isotope Composition
Isotope
Sulfur-32
Bromine79
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Electrons
Protons
Neutrons
Isotopes &
Their Uses
Heart scans with
radioactive
technetium-99.
99
43Tc
Emits gamma rays
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Masses of Isotopes
determined with a mass spectrometer
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Mass spectrum of C6H5Br
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11B
Isotopes
10B
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value.
• Average mass = ATOMIC WEIGHT
• Boron is 19.9% 10B and 80.1% 11B. That is, 11B
is 80.1 percent abundant on earth.
• For boron atomic weight
= 0.199 (10.0 u) + 0.801 (11.0 u) = 10.8 u
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Isotopes & Atomic Weight
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value.
• 6Li = 7.5% abundant and 7Li = 92.5%
–Atomic weight of Li = ______________
•
28Si
= 92.23%, 29Si = 4.67%, 30Si = 3.10%
–Atomic weight of Si = ______________
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Counting Atoms
Mg burns in air (O2) to
produce white
magnesium oxide, MgO.
How can we figure out how
much oxide is produced
from a given mass of Mg?
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Counting Atoms
Chemistry is a quantitative
science—we need a
“counting unit.”
MOLE
1 mole is the amount of
substance that contains as
many particles (atoms,
molecules) as there are in
12.0 g of 12C.
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518 g of Pb, 2.50 mol
Particles in a Mole
Avogadro’s Number
Amedeo Avogadro
1776-1856
6.02214199 x
23
10
There is Avogadro’s number of
particles in a mole of any substance.
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Molar Mass
1 mol of 12C
= 12.00 g of C
= 6.022 x 1023 atoms
of C
12.00 g of 12C is its
MOLAR MASS
Taking into account all
of the isotopes of C,
the molar mass of C is
12.011 g/mol
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One-mole Amounts
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PROBLEM: What amount of Mg
is represented by 0.200 g? How
many atoms?
Mg has a molar mass of 24.3050 g/mol.
1 mol
0.200 g •
= 8.23 x 10-3 mol
24.31 g
How many atoms in this piece of Mg?
23 atoms
6.022
x
10
8.23 x 10-3 mol •
1 mol
= 4.95 x 1021 atoms Mg
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Periodic Table
• Dmitri Mendeleev developed the
modern periodic table. Argued
that element properties are
periodic functions of their atomic
weights.
• We now know that element
properties are periodic functions
of their ATOMIC NUMBERS.
• See CD-ROM, Screen 2.16.
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Periods in the Periodic Table
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Groups/Families in the
Periodic Table
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Regions of the Periodic Table
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Element Abundance
C
O
Al
Si
http://www.webelements.com/
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Fe
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Hydrogen
Shuttle main engines
use H2 and O2
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Group 1A: Alkali Metals
Li, Na, K, Rb, Cs
Reaction of
potassium + H2O
Cutting sodium metal
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Group 2A: Alkaline Earth Metals
Be, Mg, Ca, Sr, Ba, Ra
Magnesium
Magnesium
oxide
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Group 3A: B, Al, Ga, In, Tl
Cu
Al
Al resists corrosion
(here in nitric acid).
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Gallium is one of the few
metals that can be liquid
at room temp.
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Gems & Minerals
• Sapphire: Al2O3
with Fe3+ or Ti3+
impurity gives
blue whereas V3+
gives violet.
• Ruby: Al2O3 with
Cr3+ impurity
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Group 4A: C, Si, Ge, Sn, Pb
Quartz, SiO2
Diamond
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Group 5A: N, P, As, Sb, Bi
Ammonia, NH3
White and red
phosphorus
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Phosphorus
• Phosphorus first isolated by Brandt from urine, 1669
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Group 6A: O, S, Se, Te, Po
Sulfuric acid dripping from
snot-tite in cave in Mexico
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Elemental S has a ring
structure.
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Group 7A:
Halogens
F, Cl, Br, I, At
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Group 8A: Noble Gases
He, Ne, Ar, Kr, Xe, Rn
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Transition Elements
Lanthanides and actinides
Iron in air gives
iron(III) oxide
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Colors of Transition Metal
Compounds
Iron
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Cobalt
Nickel
Copper
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Zinc