chemistry 1 - atomic structure
DESCRIPTION
Structure of Atoms and Ions, Electron Arrangements and IsotopesTRANSCRIPT
Structure of the Atom
Introductory Chemistry
Atomic Structure
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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!!
An atom consists of • a nucleus (of protons and neutrons) • electrons in space about the
nucleus.
The Anatomy of an Atom
Nucleus
Electron cloud
Subatomic
components
Relative Mass
Charge
nucleus
Proton 1 +1
Neutron
1 0
Orbital
cloud
Electron
0.005 -1
Features of the Atom
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.
Mass Number• mass number A = protons +
neutrons• always a whole number
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• NOT the value given on the Periodic Table!
Atomic Number• atomic number z = protons
• always a whole number
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• identifies the element
Practice: Lithium has the atomic number 3 and mass number 7
– # of protons:
– # of neutrons:
– # of electrons:
3
4
3
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
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
Ions
• ions are electrically charged atoms
Neutral atom
negative ionpositive ion
lose electrons
gain electrons
p+ > e- p+ < e-
cation anion
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
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
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?
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
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
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
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
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
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