Atomic Structure
Nuclear and Electronic
Organization
Atoms
Notion dates from ca 400 BCE Democritus
 Notion lay dormat 2200 years until early
1800’s - John Dalton

John Dalton
1766-1844
Dalton’s Theory
Explained Conservation of Mass in
chemical and physical changes
 Accounted for differences between
elements and compounds
 Accounted for constant composition of
compound substances. Water, eg,
always 88.9% oxygen and 11.1%
hydrogen

Atoms
Incredibly small
 Sub-microscopic
 Yet much is understood, measurable of
sub-atomic structure

Two Major Zones or Regions

Nucleus
– Dense, central core
– Almost all of the atomic mass
– only about 1-trillionth of the space or
volume

Extranuclear, or electron, region
– Most of the atomic volume
– Almost none of the atom’s mass
– Almost “empty space”
Atom
Nucleus
Extra-nuclear
(electron) region
Three Sub-atomic Particles


– positive (+1)
– part of nucleus
– 1.0 amu
Electrons
– negative (-1)
– negligible mass (0.0 amu)
– outside nucleus
Protons

Neutrons
– neutral
– part of nucleus
– 1.0 amu
Atoms of Various Elements

Same no. of p+ for given element
– equal to atomic number
– equal to e- no. for neutral atoms

Neutron nos. may vary for atoms of
same element
– isotopes
– average no. of neutrons determinable from
atomic mass info
17
No. of protons
Average mass,
average total of p+ & n
35.453
17
No. of protons
Average no neutrons 
18.5
35.453
Two Isotopes for Cl
Cl-35 or
35
Cl
Cl-37 or
37
Cl
17
17
17 p+
18n
17 p+
20n
Mass = 35 amu
ca 75% of isotopes
Mass = 37 amu
ca 25% of isotopes
Average mass = 35.453
12
No. of protons
Average
no
neutrons 
12.3053
24.3050
Three Isotopes for Mg
24
Mg-24 or Mg
25
Mg-25 or Mg
26
Mg-26 or Mg
12
12
12
12 p+
12n
12 p+
13n
12 p+
14n
Mass = 25 amu
ca 10% of isotopes
Mass = 26 amu
ca 11% of isotopes
Mass = 24 amu
ca 79% of isotopes
Average mass = 24.3050
Electron Organization
Outside nucleus
 Grouped in increasing levels of energy
 Lowest-energy e- nearest nucleus
 Limited no. e- at each level (more at
higher levels)
 Transitions of e- between levels absorb
or release energy

Energy Levels
Levels
approach a
continuum for
most atoms
beyond then
10th level.
1
2
3
4
5
6 7
8, 9, 10, etc
Electron Transitions
Energy absorbed
•
•
1
2
3
4
5
6 7
8, 9, 10, etc
Electron Transitions
•
•
1 Energy released
2
3
4
5
6 7
8, 9, 10, etc
Electron Transitions
Give rise to absorption and emission
spectra
 Only certain colors (or wavelengths)
observed for given element
 Spectrum (color set) for each element
can be used to identify element in
unknown sample

Spectra
Spectra
Spectra
Maximum Occupancy of
Energy Levels
Level 1 -- 2 e Level 2 -- 8 e Level 3 -- 18 e Level 4 -- 32 e…
 Level n -- 2 x n2 e Actual occupancy  32 e
Energy Levels
8e
18e- 32eLevels
approach a
continuum for
most atoms
beyond then
10th level.
2e1
2
3
4
5
6 7
8, 9, 10, etc
Lithium
2e- 1e-
Same as:
Li 2, 1
3
Nitrogen
2e- 5e-
Same as:
N 2, 5
7
Neon
2e- 8e-
Same as:
Ne 2, 8
10
Largest atom for which
all electrons exist only
at main levels 1 and 2.
Sodium
2e-
1e8e-
Same as:
Na 2, 8, 1
11
Smallest atom for which
an electron must exist at
main level 3.
Argon
2e-
8e8e-
Same as:
Ar 2, 8, 8
18
Largest atom for which all
electrons can exist within
first three main levels.
Atoms with At. No. > 18
“Filling order”:
Level 1 - 2eLevel 2 - 8eLevel 3 - 8eLevel 4 - 2eLevel 3 - up to 18 total
2e-
8e8e-
Although level
#3 can have 18
total electrons,
level #4 must
contain next 2
electrons;
additional
electrons after
the 20th go back
to level #3 (up to
18, maximum).
Potassium
1e2e-
8e8e-
Same as:
K 2, 8, 8, 1
19
Smallest atom for which
energy level 4 must be
occupied.
Iron
2e2e-
Filling:
1st 18e-: 2,8,8
Next 2e-: 2,8,8,2
Last 6e-: 2, 8, 14, 2
14e-
Same as:
8e-
Fe 2, 8, 14, 2
26
Zinc
2e2e-
Filling:
1st 18e-: 2,8,8
Next 2e-: 2,8,8,2
Last 10e-: 2, 8, 18, 2
18e-
Same as:
8e-
Zn 2, 8, 18, 2
30
Good News!

Our requirements for electron
configurations are – limited to 30 e-, total (Zn)
– involve main levels only (no s, p, d, f
“orbital” or “subshell” configurations
required)

Much of electron configuration
determinable from Periodic Table
I
Periodic Table of the Elements
VIII
1
1
H
II
2
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
3
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
4
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31 32
Ga Ge
33
As
34
Se
35
Br
36
Kr
5
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
6
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
88
Ra
89
Ac
104
105
106
107
108
109
110
111
7
87
Fr
III IV V VI VII
112
2
He
“Periodic” Properties
Properties of the elements that change
periodically (cyclically) as the atomic
number increases.
 Examples

– Chemical reactivity
– Atomic size (diameter, radius, eg.)
– Ionization energy
– Electronegativity
– Metallic/non-metallic character
Chemical Reactivity

Properties are similar for elements in
same family or vertical group.
– Group I: Li, Na, K, etc
– Group II: Be, Mg, Ca, etc
– Group VII: F, Cl, Br, I, etc
Similar kinds of reactions
 Similar kinds of compounds

Requires warm
water; sluggish
Similar Reactions
Vigorous in
cool water;
may explode
Consider Group I: Li, Na, K, Rb, Cs
Explosion
Li + H2O  explosive gas, alkaline solution likely; very
dangerous
Na + H2O  explosive gas, alkaline solution
K + H2O  explosive gas, alkaline solution
Run! Call 911
Rb + H2O  explosive gas, alkaline solution
Cs + H2O  explosive gas, alkaline solution
Our condolences.
Similar Compounds
Again, consider Group I: Li, Na, K, Rb, Cs
“Sulfides”: Li2S, Na2S, K2S, Rb2S, Cs2S
“Chlorides”: LiCl, NaCl, KCl, RbCl, CsCl
“Phosphates”: Li3PO4, Na3PO4, K3PO4, Rb3PO4, etc
Similar Compounds
For Group II: Be, Mg, Ca, Sr, Ba
“Sulfides”: BeS, MgS, CaS, SrS, BaS
“Chlorides”: BeCl2, MgCl2, CaCl2, SrCl2, BaCl2
“Phosphates”: Be3(PO4)2, Mg3(PO4)2, Ca3(PO4)2, etc
Atomic Size
1
H
3
Li
small
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31 32
Ga Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
LARGE
112
Atomic Diameter
2e-1e-
2e- 1e8e
-
1e8e
2e 8e
Same as:
3Li
Same as:
11Na
2, 1
2, 8, 1
Increases
going
down a
“family”
or group.
More
energy
levels
Same as: 19 K 2, 8, 8,1 occupied.
Atomic Diameter
6+ -
9+
Same as:
Same as:
Same as:
3Li
6C
9F
3+ 2e
2e 4e-
1e-
2, 1
2, 4
2e-7e-
2, 7
Diameter shrinks going rightward across a period.
Atomic Diameter
3+ 2e-1e-
11+2e- 1e
8e-
-
8e19+2e- 1e- 8e
“Shielding
by “core”
electrons
Same as: 3Li 2, 1
keeps
Approx +1 at outer level
effective
charge at
Same as: 11Na 2, 8, 1 outer level
about the
Approx +1 at outer level
same
within a
family or
Same as: 19 K 2, 8, 8,1
group.
Approx +1 at outer level
Ionization Energy (Potential)

Minimum energy required to remove
Ion -- at atom
electron from gaseous atom:
(or group of
X(g) + I.E.  e- + X+(g)

atoms) with
net charge
I.E. is high for atoms which hold very
tightly to their outer electrons
– non-metals have high I.E.’s; metals, low
– highest for smallest atoms.
Small size
1
H
3
Li
Ionization Energy LARGE I.E.
2
He
4
Be
11 12
Na Mg
5
B
6
C
7
N
8
O
9
F
10
Ne
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31 32
Ga Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89
Ac
104
105
106
107
108
109
110
111
LARGE
SIZE
small I.E.
112
Electronegativity
Tendency of atom to hold to its electron
when sharing electrons with
neighboring atom.
 Generally, follow same trends as I.E.
 Important for bonding polarity (next
unit of study)

Metallic Character
1
H
3
Li
2
He
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11 12
Na Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31 32
Ga Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
57
La
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79 80
Au Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
89 104 105 106 107 108 109 110 111 112
Ac Rf Db Sg Bh Hs Mt