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Chapter 4 Atoms and
Elements
• Elements and Symbols
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The Periodic Table
The Atom
Atomic and Mass Numbers
Isotopes and Atomic Mass
Electron Energy Levels
You will need your textbook or copy of a periodic table for class !!!!!!!!!!
Pure Substances
• Elements
• Compounds
Elements
Elements are
• Pure substances that cannot be separated into
simpler substances by ordinary laboratory
processes.
• The building blocks of matter.
gold
carbon
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
aluminum
Sources of Some Element
Names
Some elements are
named for
• planets,
• mythological
figures,
• minerals,
• colors,
• scientists, and
• places.
Historical Perspective
Symbols of Elements
A symbol
• Represents the name of an element.
• Consists of 1 or 2 letters.
• Starts with a capital letter.
Examples:
1-Letter Symbols
C carbon
N nitrogen
F fluorine
O oxygen
2-Letter Symbols
Co cobalt
Ca calcium
Al
aluminum
Mg magnesium
Symbols from Latin Names
Several symbols are derived from Latin names
as shown below:
Cu, copper (cuprum)
Au, gold (aurum)
Fe, iron (ferrum)
Ag, silver (argentum)
Pure Substances
A pure substance is classified as
• An element when composed of one
type of atom.
• A compound when composed of two or
more different elements combined in a
definite ratio.
Elements v. Compounds v.
Mixtures: Review
• Recall definition of compound.
– A compound is when two or more different
elements combine in a definite ratio.
NaCl
MgCl2
AlCl3
• Molecular element is when both of the atoms
in the molecule are the same element.
H2
N2
O2
F2
Cl2
Br2
I2
A closer look at
the Periodic Table
Modern
Periodic Table
• Mendeleev – Father of the Periodic Table
• Periodic Law of the Elements – when elements are arranged
in a particular order (increasing atomic number), elements of
similar properties occur at periodic intervals
• Arranged into:
– Groups/families – vertical columns
– Periods – horizontal rows
http://www.woodrow.org/teachers/chemistry/institutes/1992/MENDELEEV.GIF
http://www.youtube.com/watch?v=fPnwBITSmgU
Arrangement of the Periodic Table
The blocks of the periodic table:
The Periodic Table – All
Stretched Out
Groups and Periods
On the periodic table
• Elements are arranged according to
similar properties.
• Groups contain elements with similar
properties in vertical columns.
• Periods are horizontal rows of elements.
Groups and Periods (Rows)
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Publishing as Benjamin Cummings
Group Numbers
Group Numbers
• Use the letter A for the representative
elements 1A to 8A and the letter B for the
transition elements.
• Also use numbers 1-18 for the columns from
left to right.
Names of Some Representative Elements
• Several groups of representative elements are
known by common names.
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Publishing as Benjamin Cummings
Alkali Metals
Group 1A(1), the alkali metals, includes
lithium, sodium, and potassium.
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
Halogens
Group 7A(17) the
halogens, includes
• chlorine,
• bromine, and
• iodine.
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Learning Check
Identify the element described by the following:
1. Group 7A (17), Period 4
A)
B)
C)
2. Group 2A(2), Period 3
A)
B)
C)
3. Group 5A(15), Period 2
A)
B)
C)
Special Element: C
Carbon is a very special element.
1. Specialized industrial uses.
•
•
elemental forms
organic molecules such as solvents,
fuels, pharmaceuticals, etc.
2. Central element in biomolecules
found in living systems.
Learning Check
Match the elements to the description:
1. Metals in Group 4A(14)
A)
B)
C)
2. Nonmetals in Group 5A(15)
A)
B)
C)
3. Metalloids in Group 4A(14)
A)
B)
C)
A closer look still
The Conjecture of Atoms
• As early as 500 B.C., Greek Philosophers
proposed that all matter is made up of atoms
– Atom:
• The smallest individual particle of an element that
maintains the properties of that element
• Atomos - indivisible
http://members.aol.com/dcaronejr/ezmed/atom.jpg
http://www.aperfectworld.org/clipart/science_technology/atom.gif
Dalton’s Law of Atomic Theory
http://www.youtube.com/watch?v=wsYDL6EjV4k
Dalton’s Law of Atomic
Theory
1. All matter is composed of
extremely small particles called
atoms.
2. Atoms of a given element are
identical in their physical and
chemical properties, while atoms
of different elements differ in
their physical and chemical
properties.
http://www.kjemi.uio.no/software/dalton/graphics/john_dalton.gif
Dalton’s Law of Atomic
Theory
3. Atoms of different elements
combine in simple, wholenumber ratios to form
compounds.
4. In chemical reactions, atoms
are combined, separated, or
rearranged but never created,
destroyed, or changed.
http://www.kjemi.uio.no/software/dalton/graphics/john_dalton.gif
Subatomic Particles
Today, we know that atoms are made up of
smaller, more fundamental particles called
subatomic particles.
Protons, Electrons & Neutrons
Subatomic Particles
Atoms contains subatomic
particles
• Protons have a positive (+)
charge.
• Electrons have a negative (-)
charge.
• Like charges repel and unlike
charges attract.
• Neutrons are neutral.
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Rutherford’s Gold-Foil
Experiment
In Rutherford’s gold-foil experiment
• Positively charged particles were aimed at atoms
of gold.
• Most went straight through the atoms.
• Only a few were deflected.
• Conclusion: There must be a small, dense,
positively charged nucleus in the atom that
deflects positive particles that come close.
Rutherford’s Gold-Foil
Experiment
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Publishing as Benjamin Cummings
Structure of the Atom
An atom consists
• Of a nucleus that
contains protons
and neutrons.
• Of electrons in
the large empty
space around
the nucleus.
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Atomic Mass Scale
On the atomic mass scale for subatomic particles
• 1 atomic mass unit (amu) is equal to 1/12 of
the mass of the carbon-12 atom.
• A proton has a mass of about 1 (1.007) amu.
• A neutron has a mass of about 1 (1.008) amu.
• An electron has a very small mass (0.00055
amu).
Particles in the Atom
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
Atomic Number
The atomic number
• Is specific for each element.
• Is the same for all atoms of an element.
• Is equal to the number of protons in an atom.
• Appears above the symbol of an element in
most periodic tables.
Atomic Number
Symbol
11
Na
Atomic Numbers and Protons
Examples:
• Hydrogen has atomic number 1, every H
atom has one proton.
• Carbon has atomic number 6, every C
atom has six protons.
• Copper has atomic number 29, every Cu
atom has 29 protons.
• Gold has atomic number 79, every Au
atom has 79 protons.
Atomic Models
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Publishing as Benjamin Cummings
Learning Check
State the number of protons in each.
1. A ________ atom
A) protons
B) protons
C)
protons
2. A ________ atom
A)
protons
B)
protons
C)
protons
3. A ________ atom
A)
protons B)
protons
C)
protons
4. A ________ atom
A)
protons
B)
protons
C)
protons
Electrons in An Atom
• An atom of any element is electrically neutral; the
net charge of an atom is zero.
• In an atom, the number of protons is equal to the
number of electrons.
number of protons = number of electrons
• For example, an atom of aluminum has 13 protons
and 13 electrons. The net charge is zero.
13 protons (13 +) + 13 electrons (13 -) = 0
• What if there are more electrons than protons? or
more protons than electrons?
Mass Number
The mass number
• Represents the number of particles in the nucleus.
• Is equal to the
Number of protons + Number of neutrons
Learning Check
An atom has 14 protons and 20 neutrons.
1. Its atomic number is
A)
B)
C)
2. Its mass number is
A)
B)
C)
B)
C)
3. The element is
A)
Learning Check
An atom of zinc has an atomic number of 30, and
mass number of 65.
1. How many protons are in this zinc atom?
A)
B)
C)
2. How many neutrons are in the zinc atom?
A)
B)
C)
3. What is the mass number of a zinc atom that
has 37 neutrons?
A)
B)
C)
Isotopes and Atomic Mass
Isotopes
• Are atoms of the same element that have
different mass numbers.
• Have the same number of protons,
• but different numbers of neutrons.
Nuclear Symbol
A nuclear symbol (aka atomic symbol)
• Represents a particular atom of an element.
• Gives the mass number in the upper left corner
and the atomic number in the lower left corner.
Example: An atom of sodium with atomic
number 11 and a mass number 23 has the
following atomic symbol:
23 Na
mass number
11
atomic number
Information from Nuclear
Symbols
• The nuclear symbol indicates the number of
protons (p+), neutrons, (n), and electrons (e-)
in a particular atom.
16
31
8
15
8 p+
8n
8 e-
15 p+
16 n
15 e-
O
P
65
30
Zn
30 p+
35 n
30 e-
Nuclear / Atomic Symbols
Mass number =
number of protons +
number of neutrons
Charge =
A
Z
Atomic number =
number of protons
Defines the
element
X
Q
Number of protons number of electrons
Nuclear / Atomic Symbols
Mass number =
number of protons +
number of neutrons
Charge =
A
Z
Atomic number =
number of protons
X
Q
number of protons –
number of electrons
Nuclear / Atomic Symbols
Mass number =
number of protons +
number of neutrons
Charge =
A
Z
Atomic number =
number of protons
X
Q
number of protons –
number of electrons
Nuclear / Atomic Symbol
Notation vs.
The Periodic Table Notation
40
20
20
2+
Ca
Ca
40.078
Learning Check
1. Which of the following pairs are isotopes of the
_________________?
2. In which of the following pairs do both atoms have
_________________?
A.
15X
8
B.
12X
6
C.
15X
7
14X
6
15X
16X
7
8
Atomic Mass
The atomic mass of an element
• Is usually listed below the symbol of each
element on the periodic table.
• Gives the mass of an “average” atom of
each element compared to 12C.
• Is not the same as the mass number.
Na
22.99
Calculating Average Atomic Mass
The calculation for the average atomic mass
requires the
• Percent (%) abundance of each isotope.
• Atomic mass in amu of each isotope of that
element.
• Sum of the weighted averages.
mass isotope(1) x (%) + mass isotope(2) x (%) + …
100
100
Consider the element Magnesium
Atomic Mass of
Magnesium
The atomic mass of Mg
• Is due to all the Mg
isotopes.
• Is a weighted
average.
• Is not a whole
number.
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Publishing as Benjamin Cummings
Calculating Atomic Mass
Isotope Mass
Abundance
24Mg
= 23.985 amu x 78.70/100
= 18.88 amu
25Mg
= 24.986 amu x 10.13/100
= 2.531 amu
26Mg
= 25.983 amu x 11.17/100
= 2.902 amu
Atomic mass (average mass) Mg
= 24.31 amu
Mg
24.31
Atomic Mass for Cl
• The atomic mass of
chlorine is the
weighted average
of two isotopes 35Cl
and 37Cl.
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Calculating Atomic Mass for Cl
35Cl
has atomic mass 34.97 (75.76%) and 37Cl has
atomic mass 36.97 (24.24%).
• The atomic mass and percent of each isotope are
used to calculate the contribution of each isotope
to the weighted average.
34.97 x 75.76
= 26.49 amu
100
36.97 x 24.24
= + 8.962 amu
100
35.45 amu
• The sum is the weighted average or atomic mass
of Cl. 35.45 amu
Learning Check
Gallium is an element found in lasers used in
compact disc players. In a sample of gallium,
there is 60.11% of 69Ga (atomic mass 68.93)
atoms and 39.89% of 71Ga (atomic mass
70.93) atoms.
What is the atomic mass of gallium?
→
Solution
69Ga
68.93 amu x
60.11
100
= 41.43 amu (from 69Ga)
71Ga
70.93 amu x 39.89 = 28.29 amu (from 71Ga)
100
31
Atomic mass Ga
= 69.72 amu
Ga
69.72
Examples of Isotopes and Their Atomic
Masses
Table 4.8
Most elements
have two or more
isotopes that
contribute to the
atomic mass of that
element.
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings