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

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Properties affecting atomic radius

1. orbital size:– What will happen to the radius as number of orbital

shells increases?

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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?

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• 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.