8. Practice: Lithium has the atomic number 3
and mass number 7
– # of protons:
– # of neutrons:
– # of electrons:
3
4
3
9. 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
10. 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
Cl37
17
11. Ions
• ions are electrically charged atoms
Neutral atom
negative ionpositive ion
lose electrons gain electrons
p+ > e-
p+ < e-
cation anion
12. 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
14. Average Relative Atomic Mass AR
• a weighted average of
all isotopes of an
element
100
(%)(mass(mass)(%) )
Avg.
Atomic
Mass
• this value is found on the Periodic Table
• based on the %
abundance data from
mass spectrometer
15. 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?
16. 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
17. Another way of looking at it
Mass Number of Isotope
Out of 100 atoms, how
many have this mass?
What would be the total
mass of these atoms?
35Cl
37Cl
18. Another way of looking at it
Mass Number of Isotope
Out of 100 atoms, how
many have this mass?
What would be the total
mass of these atoms?
35Cl 75
37Cl 25
19. Another way of looking at it
Mass Number of Isotope
Out of 100 atoms, how
many have this mass?
What would be the total
mass of these atoms?
35Cl 75 35 × 75 = 2625
37Cl 25 37 × 25 = 925
20. Another way of looking at it
Mass Number of Isotope
Out of 100 atoms, how
many have this mass?
What would be the total
mass of these atoms?
35Cl 75 35 × 75 = 2625
37Cl 25 37 × 25 = 925
Total mass of 100 atoms 3550
21. Another way of looking at it
Mass Number of Isotope
Out of 100 atoms, how
many have this mass?
What would be the total
mass of these atoms?
35Cl 75 35 × 75 = 2625
37Cl 25 37 × 25 = 925
Total mass of 100 atoms 3550
Average mass of 1 atom 35.5