Download Symbols of Elements

Chapter 3 Atoms and Elements
3.4
The Atom
Copyright © 2009 by Pearson Education, Inc.
1
Dalton’s Atomic Theory
In Dalton’s atomic theory, atoms
• are tiny particles of matter.
• of an element are similar 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.
2
Subatomic Particles
Atoms contain subatomic particles.
•
•
•
•
Protons have a positive (+) charge.
Electrons have a negative (-) charge.
Neutrons are neutral.
Like charges repel and unlike charges
attract.
3
Rutherford’s Gold Foil Experiment
In Rutherford’s gold foil experiment, positively
charged particles
•
were aimed at atoms of gold.
•
mostly went straight through the atoms.
•
were deflected only occasionally.
Conclusion:
There must be a small, dense, positively
charged nucleus in the atom that deflects
positive particles that come close.
4
Rutherford’s Gold Foil Experiment
Copyright © 2009 by Pearson Education, Inc.
5
Structure of the Atom
An atom consists
• of a nucleus that
contains protons
and neutrons.
• of electrons in a
large, empty
space around the
nucleus.
Copyright © 2009 by Pearson Education, Inc.
6
Atomic Mass Scale
On the atomic mass scale,
• 1 atomic mass unit (amu) has a mass 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, 0.000 549 amu.
7
Particles in the Atom
8
Learning Check
Identify each statement as describing a
1) proton, 2) neutron, or 3) electron.
A. found outside the nucleus
B. has a positive charge
C. is neutral
D. found in the nucleus
9
Learning Check

Is each of the following statements true
or false?
Protons are heavier than electrons
 Protons are attracted to neutrons
 Electrons are small that they have no
electrical charge
 The nucleus contains all the protons and
neutrons of an atom

10
Chapter 3 Atoms and Elements
3.5
Atomic Number and Mass Number
Copyright © 2009 by Pearson Education, Inc.
11
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.
Atomic Number
Symbol
11
Na
12
Atomic Number and Protons
Examples of atomic number and number of protons:
• 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.
13
Learning Check
State the number of protons in each.
A. A nitrogen atom
1) 5 protons
2) 7 protons
3) 14 protons
B. A sulfur atom
1) 32 protons
2) 16 protons
3) 6 protons
C. A barium atom
1) 137 protons
2) 81 protons
3) 56 protons
14
Electrons in An Atom
An atom
• of an element is electrically neutral; the net charge
of an atom is zero.
• has an equal number of protons and electrons.
number of protons = number of electrons
Aluminum has 13 protons and 13 electrons. The net
(overall) charge is zero.
13 protons (13+) + 13 electrons (13 -) = 0
15
Mass Number
The mass number
• represents the number of particles in the nucleus.
• is equal to the number of protons + the number
of neutrons.
16
Atomic Models
17
Study Tip: Protons and Neutrons
Number of protons = Atomic number
Number of protons + neutrons = Mass number
Number of neutrons
= mass number – atomic number (protons)
Note: Mass number is given for specific isotopes only.
18
Learning Check
An atom of zinc has a mass number of 65.
A. How many protons are in this zinc atom?
1) 30
2) 35
3) 65
B. How many neutrons are in the zinc atom?
1) 30
2) 35
3) 65
C. What is the mass number of a zinc atom that has
37 neutrons?
1) 37
2) 65
3) 67
19
Learning Check
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14
2) 16
3) 34
B. Its mass number is
1) 14
2) 16
3) 34
2) Ca
3) Se
C. The element is
1) Si
20
Chapter 3 Atoms and Elements
3.6
Isotopes and Atomic Mass
24Mg
25Mg
26Mg
12
12
12
Copyright © 2009 by Pearson Education, Inc.
21
Isotopes
Isotopes
• are atoms of the same element that have different
mass numbers.
• have the same number of protons, but different
numbers of neutrons.
22
Atomic Symbol
An 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:
mass number
23
Na
atomic number
11
23
Information from Atomic Symbols
The atomic symbol for a specific atom of an element
gives the
• number of protons (p+),
• number of neutrons (n),
• and number of electrons (e-).
24
Information from Atomic Symbols
Examples of number of subatomic particles for atoms
Atomic symbol
16
8
31
O
8 p+
8n
8 e-
P
15
15 p+
16 n
15 e-
65
Zn
30
30 p+
35 n
30 e-
25
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:
12C
6
13C
14C
6
6
protons
______
______
______
neutrons
______
______
______
electrons ______
______
______
26
Learning Check
Write the atomic symbols for atoms with the
following subatomic particles:
A. 8 p+, 8 n, 8 e-
___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 47 e-
___________
27
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?
A.
15X
8
B.
C.
12X
15X
7
14X
6
6
15X
16X
7
8
28
Isotopes of Magnesium
29
Isotopes of Magnesium
30
Isotopes of Sulfur
A sample of naturally
occurring sulfur contains
several isotopes with the
following abundances
Isotope % abundance
32S
95.02
33S
0.75
34S
4.21
36S
0.02
32S, 33S, 34S, 36S
16
16
16
16
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31
Atomic Mass
The atomic mass of an element
• is listed below the symbol of each element
on the periodic table.
• gives the mass of an “average” atom of
Na
22.99
each element compared to 12C.
• is not the same as the mass number.
32
Isotopes of Some Elements and
Their Atomic Mass
Most elements have two or more isotopes that
contribute to the atomic mass of that element.
33
Atomic Mass for Cl
The atomic mass of chlorine is
• due to all the Cl isotopes.
• not a whole number.
• the average of two isotopes:
35Cl
and 37Cl.
34
Learning Check
Using the periodic table, specify the atomic mass of
each element.
A. calcium
__________
B. aluminum
__________
C. lead
__________
D. barium
__________
E. iron
__________
35
Calculating Atomic Mass
The calculation for atomic mass requires the
• percent(%) abundance of each isotope.
• atomic mass of each isotope of that element.
• sum of the weighted averages.
mass of isotope(1)x (%) + mass of isotope(2) x (%) +
100
100
36
Calculating Atomic Mass for Cl
35Cl
has atomic mass 34.97 amu (75.76%) and 37C
has atomic mass 36.97 amu (24.24%).
• Use atomic mass and percent of each isotope 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
=
8.961 amu
100
• Sum is atomic mass of Cl
35.45 amu
37
Calculating Atomic Mass Mg
Isotope Mass
Abundance
24Mg
= 23.99 amu x 78.70/100
= 18.88 amu
25Mg
= 24.99 amu x 10.13/100
= 2.531 amu
26Mg
= 25.98 amu x 11.17/100 =
Atomic mass (average mass) Mg
2.902 amu
= 24.31 amu
38
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.
39
Learning Check
Gallium is an element found in lasers used in compact
disc players. In a sample of gallium, there is 60.10%
of 69Ga (atomic mass 68.926) atoms and 39.90% of
71Ga (atomic mass 70.925) atoms.
What is the atomic mass of gallium?
40
Chapter 3 Atoms and Elements
3.7
Electron Energy Levels
Copyright © 2009 by Pearson Education, Inc.
41
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.
42
Energy Levels
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
43
Orbitals
An orbital
• is a three-dimensional space around a nucleus,
where an electron is most likely to be found.
• has a shape that represents electron density (not
a path the electron follows).
• can hold up to 2 electrons.
44
Orbitals
An s orbital
•has a spherical shape around the nucleus.
•is found in each energy level.
A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level from n = 2.
45
Orbitals
46
Electron Level Arrangement
In the electron level arrangement for the first 18
elements
• electrons are placed in energy levels (1, 2, 3, etc.),
beginning with the lowest energy level
• there is a maximum number in each energy level.
Energy level
Number of electrons
1
2 (up to He)
2
8 (up to Ne)
3
8 (up to Ar)
4
2 (up to Ca)
47
Learning Check
Write the electron level arrangement for each:
1. N
2. Cl
3. K
48
Learning Check
Identify the element with each electron level
arrangement:
1. 2, 2
2. 2, 8, 3
3. 2, 7
49
Chapter 3 Atoms and Elements
3.8
Periodic Trends
Copyright © 2009 by Pearson Education, Inc.
50
Valence Electrons
The valence electrons
• determine the chemical properties of the elements.
• are the electrons in the highest energy level.
• are related to the group number of the element.
Example: Phosphorus has 5 valence electrons.
5 valence electrons
P in Group 5A(15)
2, 8, 5
51
Groups and Valence Electrons
All the elements in a group have the same number of
valence electrons.
Example: Elements in group 2A (2) have two (2)
valence electrons.
Be
2, 2
Mg
2, 8, 2
Ca
2, 8, 8, 2
Sr
2, 8, 18, 8, 2
52
Periodic Table and Valence
Electrons
Representative Elements Group Numbers
1
2
3
4
5
6
7
H
1
Li
2,1
Be
2,2
B
2,3
C
2,4
N
2,5
Na
Mg Al
Si
2,8,1 2,8,2 2,8,3 2,8,4
P
2,8,5
O
2,6
S
2,8,6
F
2,7
8
He
2
Ne
2,8
Cl
Ar
2,8,7 2,8,8
53
Learning Check
State the number of valence electrons for each.
A. O
1) 4
2) 6
3) 8
B. Al
1) 13
2) 3
3) 1
2) 5
3) 7
C. Cl
1) 2
54
Learning Check
State the number of valence electrons for each.
A. calcium
1) 1
2) 2
3) 3
B. group 6A (16)
1) 2
2) 4
3) 6
C. tin
1) 2
2) 4
3) 14
55
Learning Check
For the element with the following electron arrangement:
1) State the number of valence electrons.
2) Identify the element.
A. 2, 8, 5
B. 2, 8, 8, 2
C. 2, 7
56
Electron-Dot Symbols
An electron-dot symbol
• shows the valence electrons
around the symbol of the
element.
• for Mg has 2 valence electrons
as single dots on the sides of
the symbol Mg.
.
.
·Mg · or Mg · or ·Mg or ·Mg
·
57
Writing Electron-Dot Symbols
Electron-dot symbols for
• groups 1A (1) to 4A (14) use single dots.
·
·
Na ·
· Mg ·
· Al ·
·C·
·
• groups 5A (15) to 7A (17) use pairs and single
dots.
··
·P·
·
··
: O·
·
58
Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have the
same number of valence electrons (dots).
Example: Atoms of elements in Group 2A (2) each
have 2 valence electrons.
· Be ·
· Mg ·
· Ca ·
· Sr ·
· Ba ·
59
Learning Check
A.
.
X is the electron-dot symbol for
1) Na
B.
..
.X.
.
1) B
2) K
3) Al
is the electron-dot symbol of
2) N
3) P
60
Atomic Size
Atomic size is described
using the atomic radius;
the distance from the
nucleus to the valence
electrons.
61
Atomic Radius Within A Group
Atomic radius increases
going down each group
of representative
elements.
62
Atomic Radius Across a Period
Going across a period from left to right,
• an increase in the number of protons increases
attraction for valence electrons.
• atomic radius decreases.
Copyright © 2009 by Pearson Education, Inc.
63
Learning Check
Select the element in each pair with the larger atomic
radius.
A.
B.
C.
Li or K
K or Br
P or Cl
64
Ionization Energy
Ionization energy is the energy it takes to remove a
valence electron.
Na(g) + Energy (ionization) -> Na+(g) + e-
65
Ionization Energy In a Group
Going up a group of
representative elements,
• the distance decreases
between nucleus and
valence electrons.
• the ionization energy
increases.
66
Ionization Energy
• Metals have
•
lower
ionization
energies.
Nonmetals
have higher
ionization
energies.
Copyright © 2009 by Pearson Education, Inc.
67
Learning Check
Select the element in each pair with the higher ionization
energy.
A.
B.
C.
Li or K
K or Br
P or Cl
68