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Power of 10
atomic view
http://micro.magnet.fsu.edu/primer
/java/scienceopticsu/powersof10/
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The Atom
The smallest part of an element
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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.
• Protons, neutrons and electrons are subatomic particles, all
elements have them.
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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.
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Particles in the Atom
are very small
1 atomic mass unit (amu) = 1/12 of mass of 1 carbon atom that has 6
protons and 6 neutrons. 1 amu = 1.66 x 10-24 g
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Learning Check
Identify each statement as describing a
1) proton
2) neutron 3) electron
A. found outside the nucleus electron
B. has a positive charge proton
C. is neutral
neutron
D. found in the nucleus Proton and neutron
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Atomic Number
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Atomic Number =
number of protons in an atom
Atomic Number
Elemental Symbol
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Na
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.
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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.
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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
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Mass Number
Mass number
of Li atom = 7
Mass number
of C atom = 12
•Mass of atom is determined by mass of nucleus.
•Mass number = number of protons + number of neutrons
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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
Aluminum has 13 protons and 13 electrons. The net
charge is zero.
13 protons (13+) + 13 electrons (13 -) = 0
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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
atomic number of Zn is 30
B. How many neutrons are in the zinc atom?
1) 30
2) 35
3) 65
65-30=35
C. What is the mass number of a zinc atom that has
37 neutrons?
1) 37
2) 65
3) 67
30protons+37 neutrons=67
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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.
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Isotopes
Same element – same number of protons
different mass number
differ in # neutrons
24Mg
12
25Mg
12
26Mg
12
Atomic symbols = isotopic
symbols for Mg isotopes
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Atomic Symbol = Isotopic Symbols
• 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.
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Carbon Isotopes
12C
6
13C
14C
6
6
protons
6 p+
6 p+
6 p+
neutrons
6n
7n
8n
electrons 6 e-
6 e-
6 e-
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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.
(Mass number is for a specific atom, i.e.
has specific # of protons and neutrons)
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Isotopes of Some Elements and
Their Atomic Mass
Most elements have two or more isotopes that
contribute to the atomic mass of that element.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Electrons are found in specific
energy levels in atom
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 ground.
• each level has sublevels.
n=4
n=3
n=2
n=1
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Valence Electrons
The valence electrons
• determine the chemical properties of the elements.
• are the electrons in the outermost energy level.
• are same as the group number of the element for
elements in main groups.
Example:
P is located in Group 5A
Phosphorus has 5 valence electrons.
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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
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Electron-Dot Symbols
An electron-dot symbol
• shows the valence electrons
around the symbol of the
element.
• for Mg has two valence
electrons as single dots on the
sides of the symbol Mg.
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Electron-Dot Symbols
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Learning Check

A.
X is the electron-dot symbol for
1) Na
2) K
3) Al

B.

X

1) B
is the electron-dot symbol of
2) N
3) P
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