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Chapter 20

The Representative Elements

Shaun Williams, PhD

Reviewing the Periodic Table Regions

The Atomic Radii of Some Representative Elements (in Picometers)

A basic table diagram showing the largest atom, cesium with a radius of 265 picometer, in the bottom left of the periodic table. The smallest atom, helium with a radius of 32 picometers, is in the upper right of the periodic table.

Concept Check

Which should be the larger atom, Na or Cl? Why?

Na

Concept Check

Which should be the larger atom, Li or Cs? Why?

Cs

Distribution (Mass Percent) of the 18 Most Abundant Element on Earth

Element Mass Percent Element Mass Percent
Oxygen 49.2 Chlorine 0.19
Silicon 25.7 Phosphorous 0.11
Aluminum 7.50 Manganese 0.09
Iron 4.71 Carbon 0.08
Calcium 3.39 Sulfur 0.06
Sodium 2.63 Barium 0.04
Potassium 2.40 Nitrogen 0.03
Magnesium 1.93 Fluorine 0.03
Hydrogen 0.87 All others 0.49
Titanium 0.58

Abundance of the Elements in the Human Body

Major Element Mass Percent Trace Elements
(in alphabetical order)
Oxygen 65.0 Arsenic
Carbon 18.0 Chromium
Hydrogen 10.0 Cobalt
Nitrogen 3.0 Copper
Calcium 1.4 Fluorine
Phosphorus 1.0 Iodine
Magnesium 0.50 Manganese
Potassium 0.34 Molybdenum
Sulfur 0.26 Nickel
Sodium 0.14 Selenium
Chlorine 0.14 Silicon
Iron 0.004 Vanadium
Zinc 0.003

Alkali Metals: Sources and Methods of Preparation

Element Source Method of Preparation
Lithium Silicate minerals such as spodumene, \( \chem{LiAl(Si_2O_6)} \) Electrolysis of molten \( \chem{LiCl} \)
Sodium \( \chem{NaCl} \) Electrolysis of molten \( \chem{NaCl} \)
Potassium \( \chem{KCl} \) Electrolysis of molten \( \chem{KCl} \)
Rubidium Impurity in lepidolite, \( \chem{Li_2(F, OH)_2Al_2(SiO_3)_3} \) Reduction of \(\chem{RbOH}\) with \(\chem{Mg}\) and \(\chem{H_2}\)
Cesium Pollucite(\( \chem{Cs_4Al_4Si_9O_26\cdot H_2O} \)) and an impurity if lepidolite Reduction of \(\chem{CsOH}\) with \(\chem{Mg}\) and \(\chem{H_2}\)

Selected Reactions of the Alkali Metals

Reaction Comment
\(\chem{2M+X_2 \rightarrow 2MX}\) \(\chem{X_2}\) is any halogen molecule
\(\chem{4Li+O_2 \rightarrow 2Li_2O}\) Excess oxygen
\(\chem{2Na+O_2 \rightarrow Na_2O_2}\)
\(\chem{M+O_2 \rightarrow MO_2}\) \(\chem{M}\) is \(\chem{K}\), \(\chem{Rb}\), or \(\chem{Cs}\)
\(\chem{2M+S \rightarrow M_2S}\)
\(\chem{6Li+N_2 \rightarrow 2Li_3N}\) \(\chem{Li}\) only
\(\chem{12M+P_4 \rightarrow 4M_3P}\)
\(\chem{2M+H_2 \rightarrow 2MH}\)
\(\chem{2M+2H_2O \rightarrow 2MOH+H_2}\)
\(\chem{2M+2H^+ \rightarrow 2M^++H_2}\) Violent reaction!

Exercise

Predict the products formed by the following reactants: \(\chem{Na_2O_2(s)+H_2O(l)}\)

\(\chem{Na_2O_2(s)+H_2O(l)\rightarrow NaOH(aq)+H_2O_2(aq)}\)

Hydrides

Exercise

Predict the products formed by the following reactants: \(\chem{LiH(s)+H_2O(l)}\)

\(\chem{LiH(s)+H_2O(l)\rightarrow H_2(g)+LiOH(aq)}\)

Alkaline Earth Metals

Selected Reactions of the Group 2A Elements

Reaction Comment
\(\chem{M+X_2 \rightarrow MX_2}\) \(\chem{X_2}\) is any halogen molecule
\(\chem{2M+O_2 \rightarrow 2MO}\) \(\chem{Ba}\) gives \(\chem{BaO_2}\) as well
\(\chem{M+S \rightarrow MS}\)
\(\chem{3M+N_2 \rightarrow M_3N_2}\) High temperatures
\(\chem{6M+P_4 \rightarrow 2M_3P_2}\) High temperatures
\(\chem{M+H_2 \rightarrow MH_2}\) \(\chem{M}\) is \(\chem{Ca}\), \(\chem{Sr}\), or \(\chem{Ba}\); high temperatures;
\(\chem{Mg}\) at high pressure
\(\chem{M+2H_2O \rightarrow M(OH)_2+H_2}\) \(\chem{M}\) is \(\chem{Ca}\), \(\chem{Sr}\), or \(\chem{Ba}\)
\(\chem{M+2H^+ \rightarrow M^{2+}+H_2}\)
\(\chem{Be+2OH^-+2H_2O \rightarrow Be(OH)_2^{2-}+H_2}\)

Ion Exchange

A Schematic Representation of a Typcical Cation Exchange Resin

Hard water contains magnesium ions and calcium ions. The resin contains simply sodium ions. When the hard water is introduced to the resin, the magnesium ions and calcium ions replace the sodium ions in the resin, thereby getting stuck in the resin. The sodium ions are left in the water, which is now soft water.

Group 3A Elements

Some Physical Properties, Sources, and Methods of Preparation of the Group 3A Elements

Element Radius
of \(\chem{M^{3+}}\)
(pm)
Ionization
Energy
(kJ/mol)
\(\mathcal{E}^\circ\,(\mathrm{V})\)
\(\chem{M^{3+}+3e^-\rightarrow M}\)
Source Method of
Preparation
Boron 20 798 - Kernite, a form of borax (\(\chem{Na_2B_4O_7\cdot 4H_2O}\)) Reduction by \(\chem{Mg}\) or \(\chem{H_2}\)
Aluminum 50 581 -1.66 Bauxite (\(\chem{Al_2O_3}\)) Electrolysis of \(\chem{Al_2O_3}\) in molten \(\chem{Na_3AlF_6}\)
Gallium 62 577 -0.53 Traces in various minerals Reduction with \(\chem{H_2}\) or electrolysis
Indium 81 556 -0.34 Traces in various minerals Reduction with \(\chem{H_2}\) or electrolysis
Thallium 95 589 0.72 Traces in various minerals Electrolysis

Selected Reactions of the Group 3A Elements

Reaction Comment
\(\chem{2M+3X_2 \rightarrow 2MX_3}\) \(\chem{X_2}\) is any halogen molecule; \(\chem{Tl}\) gives \(\chem{TlX}\) as well, but no \(\chem{TlI_3}\)
\(\chem{4M+3O_2 \rightarrow 2M_2O_3}\) High temperatures; \(\chem{Tl}\) gives \(\chem{Tl_2O}\) as well
\(\chem{2M+3S \rightarrow M_2S_3}\) High temperatures; \(\chem{Tl}\) gives \(\chem{Tl_2S}\) as well
\(\chem{2M+N_2 \rightarrow 2MN}\) \(\chem{M}\) is \(\chem{Al}\) only
\(\chem{2M+6H^+ \rightarrow 2M^{3+}+3H_2}\) \(\chem{M}\) is \(\chem{Al}\), \(\chem{Ga}\), or \(\chem{In}\); \(\chem{Tl}\) gives \(\chem{Tl^+}\)
\(\chem{2M+2OH^-+6H_2O \rightarrow 2M(OH)_4^-+3H_2}\) \(\chem{M}\) is \(\chem{Al}\) or \(\chem{Ga}\)

Group 4A Elements

Some Physical Properties, Sources, and Methods of Preparation of the Group 4A Elements

Element Electronegativity Melting Point (\({}^\circ \mathrm{C}\)) Boiling Point (\({}^\circ \mathrm{C}\)) Source Method of Preparation
Carbon 2.6 3727 (sublimes) - Graphite, diamond, petroleum, coal -
Silicon 1.9 1410 2355 Silicate minerals, silica Reduction of \(\chem{K_2SiF_6}\) with \(\chem{Al}\), or reduction of \(\chem{SiO_2}\) with \(\chem{Mg}\)
Germanium 2.0 937 2830 Germinate (mixture of copper, iron, and germanium sulfides) Reduction of \(\chem{GeO_2}\) with \(\chem{H_2}\) or \(\chem{C}\)
Tin 2.0 327 2270 Cassiterite (\(\chem{SnO_2}\)) Reduction of \(\chem{SnO_2}\) with \(\chem{C}\)
Lead 2.3 327 1740 Galena (\(\chem{PbS}\)) Reduction of \(\chem{PbS}\) with \(\chem{O_2}\) to form \(\chem{PbO_2}\) and then reduction with \(\chem{C}\)

Selected Reactions of the Group 4A Elements

Reaction Comment
\(\chem{M+2X_2 \rightarrow MX_4}\) \(\chem{X_2}\) is any halogen molecule; \(\chem{M}\) is \(\chem{Ge}\) or \(\chem{Sn}\); \(\chem{Pb}\) gives \(\chem{PbX_2}\)
\(\chem{M+O_2 \rightarrow MO_2}\) \(\chem{M}\) is \(\chem{Ge}\) or \(\chem{Sn}\); high temperatures; \(\chem{Pb}\) gives \(\chem{PbO}\) or \(\chem{Pb_3O_4}\)
\(\chem{M+2H^+ \rightarrow M^{2+}+H_2}\) \(\chem{M}\) is \(\chem{Sn}\) or \(\chem{Pb}\)

Group 5A Elements

Some Physical Properties, Sources, and Methods of Preparation of the Group 5A Elements

Element Electronegativity Source Method of Preparation
Nitrogen 3.0 Air Liquifaction of Air
Phosphorus 2.2 Phosphate rock (\(\chem{Ca_3(PO_4)_2}\)), fluorapatite (\(\chem{Ca_5(PO_4)_3F}\)) \(\chem{2Ca_3(PO_4)_2+6SiO_2 \rightarrow 6CaSiO_3+P_4O_{10}}\) \(\chem{P_4O_{10}+10C\rightarrow 4P+10CO}\)
Arsenic 2.2 Arsenopyrite (\(\chem{Fe_3As_2}\), \(\chem{FeS}\)) Heating arsenopyrite in the absence of air
Antimony 2.1 Stibnite (\(\chem{Sb_2S_3}\)) Roasting \(\chem{Sb_2S_3}\) in air to form \(\chem{Sb_2O_3}\) and then reduction with carbon
Bismuth 2.0 Bismite (\(\chem{Bi_2O_3}\)), bismuth glance (\(\chem{Bi_2S_3}\)) Roasting \(\chem{Bi_2S_3}\) in air to form \(\chem{Bi_2O_3}\) and then reduction with carbon

Nitrogen

Nitrogen Fixation

The Nitrogen Cycle

Nitrogen gas in the atmosphere is converted by nitrogen-fixing plants to plant and animal protein. This protein eventually decays to ammonia. Bacteria convert the ammonia to nitrites. Other bacteria convert the nitrites into nitrates. Denitrifying bacteria then convert the nirates into atmoshperic nitrogen.

Nitrogen Hydrides

Nitrogen Oxides

Nitrogen Oxyacids

The Ostwald Process

An impure mixture of hydrogen and nitrogen gas is cleaned to remove unwanted gases. The pure hydrogen and nitrogen gas mixture is sent into catalytic reactors which convert it to ammonia gas. The ammonia gas is sent to a cooling chamber. In the cooling chamber about 20% of the ammonia gas is converted to liquid. The rest is mixed which atmoshperic gases and sent back into the cycle along with any unreacted hydrogen and nitrogen gas from the catalytic reactors.

Allotropes of Phosphorus

Allotropes of Phosphorus

Comparison of the three crystal structures of phosphorus. Both white and red phosphorus have a tetrahedral arrangement of their atoms. Black phosphorus has a more square arrangement of the atoms.

  1. \(\chem{P_{white}}\)
  2. \(\chem{P_{black}}\)
  3. \(\chem{P_{red}}\)

Phosphorus Oxyacids

The Group 6A Elements

Some Physical Properties, Sources, and Methods of Preparation of the Group 6A Elements

Element Electronegativity Radius of \(\chem{X^{2-}}\) (pm) Source Method of Preparation
Oxygen 3.4 140 Air Distillaton from liquid air
Sulfur 2.6 184 Sulfur deposits Melted with hot water and pumped to the surface
Selenium 2.6 198 Impurity in sulfide ores Reduction of \(\chem{H_2SeO_4}\) with \(\chem{SO_2}\)
Tellurium 2.1 221 Nagyagite (mixed sulfide and telluride) Reduction of ore with \(\chem{SO_3}\)
Polonium 2.0 230 Pitchblende

Oxygen

Ozone

The two resonance structure of ozone. The structure flip the double bond between oxygen atoms numbered 1 and 2 versus atoms numbered 2 and 3.

$$ \begin{align} & \chem{3O_2(g) \rightleftharpoons 2O_3(g)\;\;\;\;K\approx 10^{-56}} \\ & \chem{O_3} \xrightarrow{h\nu} \chem{O_2+O} \end{align} $$

Sulfur

Frasch Process

Superheated water and air is pumped underground into a deposit of sulfur. The sulfur melts and is pushed up and out of the group by the air.

Aggregates of Sulfur

Different structures of solid sulfur. Some sulfur exists as rings of eight sulfur atoms while other sulfur exists as random chains of sulfur atoms.

Sulfur Oxide Reactions

$$ \begin{align} \chem{2SO_2(g)+O_2(g)} & \rightarrow \chem{2SO_3(g)} \\ \chem{SO_2(g)+H_2O(l)} & \rightarrow \chem{H_2SO_3(aq)} \\ \chem{SO_3(g)+H_2O(l)} & \rightarrow \chem{H_2SO_4(aq)} \end{align} $$

Halogens

Trends in Selected Physical Properties of the Group 7A Elements

Element Electronegativity Radius of \(\chem{X^-}\) (pm) \(\mathcal{E}^\circ\) (V) for \(\chem{X_2+2e^- \rightarrow 2X^-}\) Bond Energy of \(\chem{X_2}\) (kJ/mol)
Fluorine 4.0 136 2.87 154
Chlorine 3.2 181 1.36 239
Bromine 3.0 195 1.09 193
Iodine 2.7 216 0.54 149
Astatine 2.2 - - -

Some Physical Properties, Sources, and Methods of Preparation of the Group 7A Elements

Element Color and State Percentage of Earth's Crust Metling Point (\({}^\circ\mathrm{C}\)) Boiling Point (\({}^\circ\mathrm{C}\)) Source Method of Preparation
Fluorine Pale yellow gas 0.07 -220 -188 Fluorospar (\(\chem{CaF_2}\)), cryolite (\(\chem{Na_3AlF_6}\)), fluorapatite (\(\chem{Ca_5(PO_4)_3F}\)) Electrolysis of molten \(\chem{KHF_2}\)
Chlorine Yellow-green gas 0.14 -101 -34 Rock salt (\(\chem{NaCl}\)), halite (\(\chem{NaCl}\)), sylvite (\(\chem{KCl}\)) Electrolysis of aqueous \(\chem{NaCl}\)
Bromine Red-brown liquid \(2.5 \times 10^{-4}\) -7.3 59 Seawater, brine wells Oxidation of \(\chem{Br^-}\) by \(\chem{Cl_2}\)
Iodine Violet-black solid \(3 \times 10^{-5}\) 113 184 Seaweed, brine wells Oxidation of \(\chem{I^-}\) by electrolysis or \(\chem{MnO_2}\)

Preparation of Hydrogen Halides

$$ \chem{H_2(g)+X_2(g)\rightarrow 2HX(g)} $$

Halogen Oxyacids and Oxyanions

The Known Oxyacids of the Halogens

Oxidation State of Halogen Fluorine Chlorine Bromine Iodine* General Name of Acids General Name of Salts
+1 \(\chem{HOF}\) \(\chem{HOCl}\) \(\chem{HOBr}\) \(\chem{HOI}\) Hypohalous acid Hypohalites, \(\chem{MOX}\)
+3 \(\chem{HOClO}\) Halous acid Halites, \(\chem{MXO_2}\)
+5 \(\chem{HOClO_2}\) \(\chem{HOBrO_2}\) \(\chem{HOIO_2}\) Halic acid Halates, \(\chem{MXO_3}\)
+7 \(\chem{HOClO_3}\) \(\chem{HOBrO_3}\) \(\chem{HOIO_4}\) Perhalic acid Perhalates, \(\chem{MXO_4}\)

* Iodine also forms \(\chem{H_4I_2O_9}\) (mesodiperiodic acid) and \(\chem{H_5IO_6}\) (paraperiodic acid).

\(\chem{HOF}\) oxidation state is best represented as -1.

Compound is unknown.

Noble Gases

Selected Properties of Group 8A Elements

Element Melting Point (\({}^\circ\mathrm{C}\)) Boiling Point (\({}^\circ\mathrm{C}\)) Atmoshperic Abundance (% by volume) Example of Compounds
Helium -270 -269 \(5 \times 10^{-4}\) None
Neon -249 -246 \(1 \times 10^{-3}\) None
Argon -189 -186 \(9 \times 10^{-1}\) \(\chem{HArF}\)
Krypton -157 -153 \(1 \times 10^{-4}\) \(\chem{KrF_2}\)
Xenon -112 -107 \(9 \times 10^{-6}\) \(\chem{XeF_4}\), \(\chem{XeO_3}\), \(\chem{XeF_6}\)

Concept Check

Which of the following groups is the most reactive? Group 1A, Group 5A, Group 6A, or Group 8A?

Group 1A Elements

Concept Check

White of the following groups does not contain at least one element that forms compounds with oxygen? Group 4A, Group 5A, Group 6A, Group 7A?

All of these groups contain at least one element that forms compounds with oxygen.

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