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Chapter 5 Atoms and Periodic Table
The Atom
1
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 in
whole number ratios to
form compounds.
 are separated, joined, or
rearranged in a chemical
reaction.
2
Atomic Size
 Smallest particle of an element that retains
the properties of that element.
 Pure copper coin the size of a penny contains
2.4 x 1022 atoms.
 1 x 108 atoms lined up next to each other
would be 1cm long.
3
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.
4
Electrons
 JJ Thomson
discovered
electrons in
1897.
 Passed electric
current through
gases at low
pressure sealed
in tubes with
electrodes at
either end.
5
Discovery of Electron
6
Electrons
 Cathode rays attracted to metal plates with a
+ charge and repelled by metal plates with –
charge.
 figured ray was made up of – charged
particles.
 Called particles electrons (e-)
7
Protons
 Atoms are electrically neutral
 If atoms contain e-, must also contain +
charged particles
 1886 Goldstein found rays traveling in
opposite direction from cathode rays (e-)
 Particles were protons (p+) (1840 x more
mass than e-)
8
Neutrons
 In 1932, James Chadwick confirmed
existence of neutrons
 No charge but mass almost equal to mass of
p+
9
Particles in the Atom
TABLE 2.6
Question – How are subatomic particles arranged?
10
Rutherford’s Gold-Foil Experiment
Theory at time was that – charges distributed evenly
throughout + charges
In Rutherford’s gold-foil experiment, positively
charged particles (He atoms w/ no electrons)
 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.
11
Rutherford’s Gold-Foil Experiment
12
Rutherford’s Gold-Foil Experiment
Click me!
13
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.
14
Atomic Mass Scale
On the atomic mass scale for subatomic particles
 1 atomic mass unit (amu) is defined as 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, 0.000549 amu.
15
Learning Check
Identify each statement as describing a
1) proton
2) neutron 3) electron
A. Found outside the nucleus.
B. Has a positive charge.
C. Is neutral.
D. Found in the nucleus.
16
Solution
Identify each statement as describing a
1) proton
2) neutron 3) electron
A. 3
B. 1
C. 2
D. 1, 2
Found outside the nucleus.
Has a positive charge.
Is neutral.
Found in the nucleus.
17
How are atoms different?
It’s the number of protons!
18
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
19
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.
20
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
21
Solution
State the number of protons in each.
A. A nitrogen atom
2) atomic number 7; 7 protons
B. A sulfur atom
2) atomic number 16; 16 protons
C. A barium atom,
3) atomic number 56; 56 protons
22
Number of 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
 Of aluminum has 13 protons and 13 electrons. The
net charge is zero.
13 protons (13+) + 13 electrons (13 -) = 0
23
Mass Number
The mass number
 Represents the number of particles in the nucleus.
 Is equal to the
Number of protons + Number of neutrons
TABLE 2.7
24
Atomic Models
25
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
26
Solution
An atom of zinc has a mass number of 65.
A. How many protons are in this zinc atom?
1) 30
(atomic number 30)
B. How many neutrons are in the zinc atom?
2) 35
(65 – 30 = 35)
C. What is the mass number of a zinc atom that has 37
neutrons?
3) 67
(30 + 37 = 67)
27
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
28
Solution
An atom has 14 protons and 20 neutrons.
A. It has atomic number
1) 14
B. It has a mass number of
3) 34
(14 + 20 = 34)
C. The element is
1) Si
(Atomic number 14)
29
Isotopes
Isotopes
 Are atoms of the same element that have different
mass numbers.
 Have the same number of protons, but different
numbers of neutrons.
30
Nuclear Symbol
A nuclear 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
31
Nuclear Symbols
For an atom, the nuclear symbol gives the number of
 Protons (p+)
 Neutrons (n)
 Electrons (e-)
16
O
31
65
P
8
15
8 p+
8n
8 e-
15 p+
16 n
15 e-
30
Zn
30 p+
35 n
30 e32
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 ______
______
______
33
Solution
12C
6
13C
14C
6
6
protons
6 p+
6 p+
6 p+
neutrons
6n
7n
8n
electrons 6 e-
6 e-
6 e-
34
Learning Check
Write the nuclear symbols for atoms with the
following subatomic particles:
A. 8 p+, 8n, 8e-
___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 47 e-
___________
35
Solution
16O
A. 8p+, 8n, 8e-
B. 17p+, 20 n, 17e-
8
37Cl
17
C. 47p+, 60n, 47e-
107Ag
47
36
Learning Check
1. Which of the following pairs are isotopes of the
same element?
2. In which of the following pairs do both atoms have
8 neutrons?
15X
A. 15X
8
B.
C.
12X
7
14X
6
6
15X
16X
7
8
37
Solution
B.
12X
6
14X
6
Both nuclear symbols represent isotopes of carbon
with six protons each, but one has 6 neutrons and the
other has 8.
C.
15X
7
16X
8
An atom of nitrogen (7) and an atom of oxygen (8)
each have 8 neutrons.
38
Elements and Isotopes
39
Isotopes of Magnesium
In naturally occurring magnesium,
there are three isotopes.
Isotopes of Mg
Atomic Mass
23.99
24.98 25.98
% abundance
78.70 10.13 11.17
24Mg
12
25Mg
12
26Mg
12
40
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
41
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.
42
Some Elements and Their Atomic
Mass
Most elements have two or more isotopes that
contribute to the atomic mass of that element.
TABLE 2.9
32.07 amu
43
Atomic Mass for Cl
The atomic mass of chlorine is
 Based on all naturally
occurring Cl isotopes.
 Not a whole number.
 The weighted average
of 35Cl and 37Cl.
44
Learning Check
Using the periodic table, give the atomic mass of
each element:
A. calcium
__________
B. aluminum
__________
C. lead
__________
D. barium
__________
E. iron
__________
45
Solution
Using the periodic table, give the atomic mass of
each element:
A. calcium
40.08 amu
B. aluminum
26.98 amu
C. lead
207.2 amu
D. barium
137.3 amu
E. iron
55.85 amu
46
Chapter 2 Atoms and Elements
2.3
The Periodic Table
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
47
Intro to Periodic Table
48
Periodic Table
 Dmitri Mendeleev listed elements in columns
in order of increasing atomic mass
 He then arranged columns so that elements
with most similar properties were next to each
other – First Periodic table
 Blank spaces left bc/ no known elements with
mass and properties that fit
 1923 Henry Moseley determined atomic
number of elements. Arranged elements in
order of atomic number instead of mass –
Modern table
49
This was my table
50
Groups and Periods
On the periodic table
 Groups contain elements with similar
properties in vertical columns.
 Periods are horizontal rows of elements.
51
Groups and Periods
Periodic Law – When the elements are arranged in order
of increasing atomic number, there is a periodic repetition
of their physical and chemical properties
52
Groups Share Similar Chemical Properties
53
Periodic Table
54
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 to the columns from left to
right.
55
Representative Elements
 Several groups of representative elements are
known by common names.
56
Alkali Metals
Group 1A(1), the alkali metals, includes lithium,
sodium, and potassium.
57
Halogens
Group 7A(17),
the halogens,
includes
chlorine,
bromine, and
iodine.
58
Learning Check
Identify the element described by the following:
A. Group 7A(17), Period 4
1) Br
2) Cl
3) Mn
B. Group 2A(2), Period 3
1) beryllium
2) magnesium
3) boron
C. Group 5A(15), Period 2
1) phosphorus 2) arsenic
3) nitrogen
59
Solution
A. Group 7A (17), Period 4
1) Br
B. Group 2A (2), Period 3
2) magnesium
C. Group 5A(15), Period 2
3) nitrogen
60
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.
61
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 of heat and
electricity.
 Are good insulators.
Metalloids
 Are better conductors than nonmetals, but not as
good as metals.
 Are used as semiconductors and insulators.
62
Comparing A Metal, Metalloid,
and Nonmetal
TABLE 2.5
63
Learning Check
Identify each of the following elements as
1) metal
2) nonmetal
3) metalloid
A. sodium
B. chlorine
C. silicon
D. iron
E. carbon
____
____
____
____
____
64
Solution
Identify each of the following elements as
1) metal
2) nonmetal
3) metalloid
A. sodium
B. chlorine
C. silicon
D. iron
E. carbon
1 metal
2 nonmetal
3 metalloid
1 metal
2 nonmetal
65
Learning Check
Match the elements to the description:
A. Metals in Group 4A(14)
1) Sn, Pb
2) C, Si
3) C, Si, Ge, Sn
B. Nonmetals in Group 5A(15)
1) As, Sb, Bi
2) N, P
3) N, P, As, Sb
C. Metalloids in Group 4A(14)
1) C, Si, Ge,
2) Si, Ge
3) Si, Ge, Sn, Pb
66
Solution
Match the elements to the description:
A. Metals in Group 4A (14)
1) Sn, Pb
B. Nonmetals in Group 5A(15)
2) N, P
C. Metalloids in Group 4A(14)
2) Si, Ge
67