Download Chapter 3 Atoms and Elements

Chapter 3
Atoms and Elements
1
Elements
Elements are
• pure substances that cannot be separated into simpler
substances by ordinary laboratory processes
• the building blocks of matter
• listed on the inside front cover of this text
2
Some Elements and Their Names
Names come from:
• planets
• mythological figures
• minerals
• colors
• geographic locations
• famous people
3
Chemical Symbols
Chemical Symbols
• represent name of element
• consist of one to two letters and start with capital
1-Letter Symbols 2-Letter Symbols
C carbon
Co cobalt
N nitrogen
Ca calcium
F fluorine
Al aluminum
O oxygen
Mg magnesium
4
Chemical Symbols from Latin Names
Ag silver, from argentum
Augold, from aurum
5
Learning Check
Write the correct chemical symbols for each of the
following elements:
A. iodine
B. iron
C. magnesium
D. zinc
E. nitrogen
6
Solution
Write the symbols for each of the following elements:
A. iodine
= I
(I2)
B. iron
= Fe
C. magnesium
= Mg
D. zinc
= Zn
E. nitrogen
= N (N2)
7
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 arranged according to
atomic size
8
Periodic Table of Elements
Group numbers
• use the letter A for
representative
elements
(Groups 1A–8A)
• use the letter B for
transition
elements
(Groups 3B–12B)
9
Group 1A, the alkali metals,
includes lithium, sodium,
potassium, rubidium, and
cesium.
Group 7A, the halogens,
includes chlorine, bromine,
and iodine.
10
Learning Check
Identify the element described by the following:
1. Group 7A, Period 4
A. Br
B. Cl
C. Mn
2. Group 2A, Period 3
A. beryllium
B. boron
C. magnesium
3. Group 5A, Period 2
A. phosphorus
B. arsenic
C. nitrogen
11
Solution
Identify the element described by the following:
1. Group 7A, Period 4
A. Br
2. Group 2A, Period 3
C. magnesium
3. Group 5A, Period 2
C. nitrogen
12
Metals, Nonmetals, and Metalloids
The heavy zigzag line separates metals and nonmetals.
• Metals are located to the left.
• Nonmetals are located to the right.
• Metalloids are located along the heavy zigzag line
between the metals and nonmetals.
13
Properties of Metals, Nonmetals, and
Metalloids
Metals
• are shiny and ductile
• are good conductors of heat and electricity
Nonmetals
• are dull, brittle, and poor conductors
• are good insulators
Metalloids
• are better conductors than nonmetals, but not as good
as metals
• are used as semiconductors and insulators
• as a general rule they have the appearance of metals
and the properties and characteristics of nonmetals
14
Comparing a Metal, Nonmetal, and
Metalloid
15
Dalton's Atomic Theory
In Dalton's atomic theory,
atoms:
• are tiny particles of matter
• of an element are similar to each
other and different from other
elements
• of two or more different elements
combine to form compounds
• are rearranged to form new
combinations in a chemical
reaction
16
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Rutherford's Gold Foil Experiment
In Rutherford’s gold foil experiment, positively charged alpha (α )
particles were aimed at atoms of gold. Most went straight
through. Occasionally one was deflected.
Conclusion:
There must be a small, dense, positively charged nucleus in the
atom that deflects positive particles that come close.
17
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Structure of the Atom
An atom consists of
• a nucleus that contains protons and neutrons
• electrons in a large, empty space around the nucleus
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Subatomic Particles in the Atom
• 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of
the carbon-12 atom.
• Protons have a
positive (+) charge.
• Electrons have a
negative (–) charge.
• Neutrons are neutral.
• Like charges repel and
unlike charges attract.
19
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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
• usually appears above the symbol of an element in the
Periodic Table
Atomic Number
Symbol
11
Na
20
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Atomic Number = Protons in Atom
For example, atomic number = number of protons:
• Atomic number H is 1; every H atom has one proton
• Atomic number of C is 6; every C atom has six protons
• Atomic number of Cu is 29; every Cu atom has 29 protons
21
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Learning Check
Use the periodic table to fill in the atomic number, number of
protons, and number of electrons for each of the following
elements: (NB: atoms have zero net charge)
Element Atomic
Number
N
Protons
Electrons
Zn
S
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Solution
Use the periodic table to fill in the atomic number, number of
protons, and number of electrons for each of the following
elements: (NB: atoms have zero net charge)
Element Atomic
Number
Protons
Electrons
N
7
7
7
Zn
30
30
30
S
16
16
16
So the number of electrons will equal the number of protons
for any neutral charge atom.
23
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Atomic Symbols and Subatomic Particles
Examples of number of subatomic particles for atoms:
Atomic symbol
16
31
O
8
8 p+
8n
8 e-
P
15
15 p+
16 n
15 e-
65
Zn
30
30 p+
35 n
30 e24
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Isotopes
Isotopes
• are atoms of the same element
• have different mass numbers
• have same number of protons but different numbers of neutrons
Mass Numbers
24
12
Mg
25
12
Mg
26
12
Mg
25
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Learning Check
Naturally occurring carbon consists of three isotopes: 12C,
13C, and 14C. State the number of protons, neutrons, and
electrons in each of the following:
Isotope
12C
13C
14C
protons
neutrons
electrons
26
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
Naturally occurring carbon consists of three isotopes: 12C,
13C, and 14C. State the number of protons, neutrons, and
electrons in each of the following:
Isotope
12C
13C
14C
protons
6
6
6
neutrons
6
7
8
electrons
6
6
6
27
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
1. Which of the pairs are isotopes of the same element?
2. In which of the pairs do both atoms have 8 neutrons?
15
A. 8
B.
12
6
C.
15
7


X
15
7
X
X
14
6
X
X
16
8
X
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Learning Check
1. Which of the pairs are isotopes of the same element?
12
6
B.
X
14
6
X
2. In which of the pairs do both atoms have 8 neutrons?
C.


15
7
X
16
8
X
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Atomic Mass
Atomic mass is the
• weighted average of all
naturally occurring
isotopes of that element
• number on the periodic
table below the chemical
symbol with two decimal
places
30
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Calculating Atomic Mass
To calculate atomic mass,
• use an experimental percent abundance of each isotope
of the element
• multiply the percent abundance by the atomic mass of
that isotope
• sum the total mass of each isotope
31
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Calculating Atomic Mass
To calculate atomic mass of Cl, use experimental data for
both isotopes of Cl:
Isotope atomic mass x % abundance
35Cl
37Cl
34.97 amu x 75.76 = 26.49 amu
100
36.97 amu x 24.24 = 8.962 amu
100
Atomic mass of Cl = 35.45 amu
32
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Electromagnetic Spectrum
As frequency increases, energy increases:
E = hν
The electromagnetic spectrum shows the arrangement of
wavelengths of electromagnetic radiation, with the visible
range from 700 to 400 nm.
33
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Elements Have a Unique Atomic Spectrum
When light from an element that is heated passes through a
prism, it separates into a unique set of distinct lines of color
called an atomic spectrum.
Strontium
Barium
34
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Electron Energy Levels
Energy levels
• are assigned numbers n = 1, 2, 3, 4,
and so on
• increase in energy as the value of n
increases
• are like the rungs of a ladder, with
the lower energy levels nearer the
nucleus
Energy levels have a maximum number of electrons equal to 2n2.
Energy level
n=1
n=2
n=3
Maximum number of electrons
2(1)2 = 2(1) = 2
2(2)2 = 2(4) = 8
2(3)2 = 2(9) = 18
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Changes in Electron Energy Level
• Electrons move to a higher
energy level when they
absorb energy.
• When electrons fall back
to a lower energy level,
light is emitted.
• The energy emitted or
absorbed is equal to the
differences between the
two energy levels.
36
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Electron Configurations in Periods
Period 1
H
1 electron in 1st energy level.
1s1
He
2 electrons in 1st energy level.
1s2
Period 2
Energy Level
1st
2nd
e- Config.
Li
2
1
1s2 2s1
Be
2
2
1s2 2s2
B
2
3
1s2 2s2 2p1
C
2
4
1s2 2s2 2p2
N
2
5
1s2 2s2 2p3
O
2
6
1s2 2s2 2p4
F
2
7
1s2 2s2 2p5
Ne
2
8
1s2 2s2 2p6
37
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Electron Configurations in Periods
Period 3
Energy Level
Na
Mg
Al
Si
P
S
Cl
Ar
1st
2
2
2
2
2
2
2
2
2nd
8
8
8
8
8
8
8
8
3rd
1
2
3
4
5
6
7
8
e- Config.
1s22s22p63s1
1s22s22p63s2
1s22s22p63s23p1
1s22s22p63s23p2
1s22s22p63s23p3
1s22s22p63s23p4
1s22s22p63s23p5
1s22s22p63s23p6
Period 4
Energy Level
1st
2nd
3rd
4th
K
Ca
2
2
8
8
8
8
1
2
[Ar]4s1
[Ar]4s2
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Electron Configurations Beyond 20
Energy Level 1st
2nd
3rd
4th
5th
6th
7th
Number of
Electrons
8
18
32
32
18
8
2
39
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Electron Orbital Filling & the Periodic Table
1s22s22p2
1s22s22p63s23p64s23d2
1s22s22p63s23p6
Learning Check
Write the electron configuration for the following elements:
C
Si
O
N
41
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
Write the electron arrangement for the following elements:
C
Si
=
=
1s2 2s2 2p2
1s22s22p63s23p2
O
As
=
=
1s2 2s2 2p4
1s22s22p63s23p64s23d104p3
U
=
[Rn] 7s26d15f3
NB: The sum of the superscripts will equal the atomic number of
the element for neutral atoms.
42
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Group Number and Valence Electrons
For representative elements in Groups 1A–8A, chemical properties
are due to the number of valence electrons.
Valence electrons are the number of electrons in the outermost
energy level (the s & p electrons for that period).
The group number gives the number of valence electrons for the
representative elements.
Group Number
1A
2A
3A
4A
5A
6A
7A
8A
# Valence Electrons
1
2
3
4
5
6
7
8
43
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Electron-Dot Symbols
Electron-dot symbols
• are also known as Lewis structures
• represent the valence electrons as dots placed on sides
of symbol
Possible electron-dot symbols for magnesium, with
the electron arrangement of 2,8,2,
• include 2 valence electrons, represented as dots
• can be drawn in more than one way
Mg
Mg
Mg
Mg
Mg
Mg
44
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Electron-Dot Symbols for Selected Elements
45
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
Question:
Write the electron-dot symbol for each of the following
elements: Cl, C, N.
Solution:
Cl
C
N
46
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Atomic Size
Atomic size
• is determined by the
atom’s atomic radius,
the distance between
nucleus and outermost
electrons
• increases for
representative
elements from top to
bottom of the periodic
table
• decreases within a
period due to
increased number of
protons in nucleus
47
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Atomic Size
48
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Ionization Energy
Ionization energy
• is the energy required to remove one of the outermost electrons from an atom
Na(g) + energy (ionization)  Na+(g) + e−
•
decreases down a group, increases across a period from left to right
49
Metallic Character
An element with metallic character is one that loses electrons
easily.
Metallic character
• is more prevalent in metals on left side of periodic table
• is less for nonmetals on right side of periodic table that do not
lose electrons easily
50
Summary of Trends in Periodic Table
51
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
Given the following elements:
C
P
Cl
Which is the largest atom?
Which has the highest ionization energy?
Which has the electron configuration 1s22s22p63s23p3
52
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
Given the following elements:
C
Which is the largest atom?
Which has the highest ionization energy?
Which belongs to Group 5A?
P
Cl
C
Cl
P
53
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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