chemistry 1 - atomic structure
DESCRIPTION
Structure of Atoms and Ions, Electron Arrangements and IsotopesTRANSCRIPT
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Structure of the Atom
Introductory Chemistry
Atomic Structure
www.pedagogics.ca
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Atoms are tiny particles!!
NUCLEUS ELECTRONS
PROTONS NEUTRONS
POSITIVE
CHARGE
ATOM
POSITIVECHARGE
PROTONS
NEUTRALCHARGE
NEUTRONS
NUCLEUS
NEGATIVE CHARGE
ELECTRONS
ATOM
Mostly empty space!!
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An atom consists of • a nucleus (of protons and neutrons) • electrons in space about the
nucleus.
The Anatomy of an Atom
Nucleus
Electron cloud
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Subatomic
components
Relative Mass
Charge
nucleus
Proton 1 +1
Neutron
1 0
Orbital
cloud
Electron
0.005 -1
Features of the Atom
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A-Z notation
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126C
mass number A
atomic number Z
element symbol
The atomic number equals the number of protons. Each element has a unique atomic number.
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Mass Number• mass number A = protons +
neutrons• always a whole number
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• NOT the value given on the Periodic Table!
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Atomic Number• atomic number z = protons
• always a whole number
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• identifies the element
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Practice: Lithium has the atomic number 3 and mass number 7
– # of protons:
– # of neutrons:
– # of electrons:
3
4
3
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Practice: Lithium has the atomic number 3 and mass number 7
– electron arrangement
(configuration)
2, 1
Lithium is in Group 1 on the Periodic Table
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Practice: electron arrangements of the first 20 elements (2,8,8,2)
• Chlorine-37– atomic #:
– mass #:
– # of protons:
– # of electrons:
– # of neutrons:
17
37
17
17
20
Cl3717
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Ions
• ions are electrically charged atoms
Neutral atom
negative ionpositive ion
lose electrons
gain electrons
p+ > e- p+ < e-
cation anion
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Practice: determine the required values for the positive calcium ion 41
Ca +2
41 Ca+2
– atomic #:
– mass #:
– # of protons:
– # of electrons:
– # of neutrons:
20
41
20
18
21
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Isotopes: Atoms of the same element with different mass numbers.
carbon-12 and carbon-14 are
isotopes
similar chemical properties
stable
radioactive
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Average Relative Atomic Mass AR
• a weighted average of all isotopes of an element
100
(%)(mass(mass)(%) )
Avg.AtomicMass
• this value is found on the Periodic Table
• based on the % abundance data from mass spectrometer
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Average Relative Atomic Mass AR or RAM
What is the relative atomic mass of chlorine?
Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37. 75% of chlorine atoms are 35Cl.
What % of chlorine atoms is 37Cl?
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Average Relative Atomic Mass AR or RAM
What is the relative atomic mass of chlorine?
Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37. 75% of chlorine atoms are 35Cl.
What % of chlorine atoms is 37Cl?
Avg.Atomic =
Mass
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Another way of looking at it
Mass Number of IsotopeOut of 100 atoms, how many have this mass?
What would be the total mass of these atoms?
35Cl37Cl
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Another way of looking at it
Mass Number of IsotopeOut of 100 atoms, how many have this mass?
What would be the total mass of these atoms?
35Cl 7537Cl 25
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Another way of looking at it
Mass Number of IsotopeOut of 100 atoms, how many have this mass?
What would be the total mass of these atoms?
35Cl 75 35 = 2625
37Cl 25 37 = 925
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Another way of looking at it
Mass Number of IsotopeOut of 100 atoms, how many have this mass?
What would be the total mass of these atoms?
35Cl 75 35 = 2625
37Cl 25 37 = 925
Total mass of 100 atoms 3550
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Another way of looking at it
Mass Number of IsotopeOut of 100 atoms, how many have this mass?
What would be the total mass of these atoms?
35Cl 75 35 = 2625
37Cl 25 37 = 925
Total mass of 100 atoms 3550
Average mass of 1 atom 35.5