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Chemical Periodicity
Chapter 6
Trends in the periodic table
•
Understand general trends in the
periodic table between
–
–
–
–
atomic radii (and ionic radii)
ionization energy
electron affinity
electronegativity.
Atomic radius
• The “bonding atomic radius” – ½ distance
between two identical atoms
• Coulombic law of attraction
kQ1Q2
F
2
r
Properties affecting atomic radius
1. orbital size:
–
What will happen to the radius as number of orbital
shells increases?
kQ1Q2
F
2
r
effective nuclear charge
• Shielding effect of core electrons (S)
• Nuclear effective charge, Zeff
• Zeff = Z – S
– What is Z? What is S?
• What happens to Zeff as we go from left to right
along the table?
• How does this affect the radius?
http://www.sartep.com/chemistryx/tutorials/tut.cfm?tutorial=atomic+radius
Isoelectronic series
• series of atoms and ions containing the same
number of electrons.
• Size is directly proportional to charge
Ionization energy: the energy required
to remove one electron from an atom
• what do you think will happen with the ionization
energy, based on what you have learned about
atomic radius?
kQ1Q2
F
2
r
• Both the atomic radius and
the type of orbital affect IE
removing more than one electron
• removing valence electrons vs. removing core
electrons
Ionization Energies in kJ/mol
1
2
3
4
5
6
7
8
H
1312
He
2372
5250
Li
520
7297
11810
Be
899
1757
14845
21000
B
800
2426
3659
25020
32820
C
1086
2352
4619
6221
37820
47260
N
1402
2855
4576
7473
9442
53250
64340
O
1314
3388
5296
7467
10987
13320
71320
84070
F
1680
3375
6045
8408
11020
15160
17860
92010
Ne
2080
3963
6130
9361
12180
15240
Na
496
4563
6913
9541
13350
16600
20113
25666
Mg
737
1450
7731
10545
13627
17995
21700
25662
http://www.shodor.org/chemviz/ionization/students/background.html
Electron affinity
• the energy
change that
occurs
when an
electron is
added to
an atom
(forming an
anion)
http://www.webelements.com/webelements/properties/text/image-intensity/electron-affinity.html
Electronegativity
• Electronegativity:
• How does this differ from electron affinity?
• General trend:
Alkali metals (column 1A)
•
•
•
•
Always form +1 ions
electron configuration:
very reactive in water
M + H2O  MOH (M = Li, Na, K, Rb, Cs)
Alkaline earth metals (2A)
• Always forms +2 ions
• electron configuration:
• Be, Mg not reactive in liquid water
Nonmetal groups
• Chalcogens (6A)
• usually form –2 ions
• electron configuration:
• Halogens (7A)
• usually form –1 ions
• electron configuration:
•
•
•
•
Noble gases (8A)
do not form ions
electronic configuration
usually unreactive, but heavier atoms (Kr, Xe, Rn) do form
compounds.
Hydrogen and the hydrides
• The text has grouped various reactions
according to those with hydrogen and
oxygen. Many of the trends we have
examined are also discussed there.
Metal hydrides
• In general:
xM(l) + H2(g) → xMH (s)
• Where M is a IA or IIA metal.
• What is x if M is
– IA?
– IIA?
Hydrides and hydroxides
• Metal hydrides react with water to form
metal hydroxides. Because of this, they
are __________. The general form is
MHx (s) + xH2O (l) → M(OH)x (s) + xH2 (g)
• Again, what is x for
– alkali metals?
– alkaline earths?
Molecular hydrides
• Halogens react with hydrogen….
H2 (g) + X2 (g)→ 2HX (g)
• These are molecular compounds. But
what happens to HCl when dissolved in
water?
• Hydrogen halides are ________.
Metals and oxygen
• Oxygen has three kinds of ions:
• Oxide:
• Peroxide:
• Superoxide:
Metal oxides in water
• Basic anhydrides:
• A basic anhydride is similar to a metal
hydroxide base, but without _______.
• Soluble metal oxides react with water to
form _____ __________ __________.
Molecular oxides
• Nonmetal reacting with water form
molecular oxides.
• These reactions are more complex; we will
discuss them later in the semester.
• However, just like molecular hydrides,
molecular oxides tend to be ___________.
combustion
• There are examples of complete
combustion and incomplete combustion of
hydrocarbons in your text. You should be
familiar with these. (p 258)
• Complete combustion of a hydrocarbon
(contains only C, H, O) will always form
____________________ as products.