Unique Nature of CarbonUnique Nature of Carbon

Carbon has two properties that Carbon has two properties that enable it to form such an extensive enable it to form such an extensive range of compounds:range of compounds:

1. Catenation – the ability to 1. Catenation – the ability to form chains of form chains of atoms. atoms.

2. The ability to form multiple 2. The ability to form multiple bonds.bonds.

CatenationCatenation

The elements nitrogen and The elements nitrogen and oxygen do not undergo extensive oxygen do not undergo extensive catenation. Compounds that contain catenation. Compounds that contain –O-O- bonds (peroxides) are typically –O-O- bonds (peroxides) are typically unstable and explode. unstable and explode.

Likewise, compounds containing Likewise, compounds containing -N-N- bonds are often explosive. An -N-N- bonds are often explosive. An example is the azide ion, Nexample is the azide ion, N33

1-1-..

CatenationCatenation

Carbon readily forms long chains of Carbon readily forms long chains of bonds with itself. This property is called bonds with itself. This property is called catenationcatenation, and is fairly unique. It results for , and is fairly unique. It results for several reasons:several reasons:

1. Carbon can make up to 4 bonds.1. Carbon can make up to 4 bonds.

2. The carbon-carbon bond is generally as 2. The carbon-carbon bond is generally as

strong as bonds between carbon and strong as bonds between carbon and otherother

elements.elements.

3. The catenated compounds are inert.3. The catenated compounds are inert.

CatenationCatenation

Silicon can also make long chains Silicon can also make long chains within its compounds, but, since the within its compounds, but, since the silicon oxygen bond is much stronger silicon oxygen bond is much stronger than that between two silicon atoms, than that between two silicon atoms, the chains typically contain –O-Si-O-Si- the chains typically contain –O-Si-O-Si- type links, rather than -Si-Si- bonds.type links, rather than -Si-Si- bonds.

Silicon also has empty low-lying Silicon also has empty low-lying dd orbitals which make its compounds orbitals which make its compounds more reactive.more reactive.

Typical Bond EnergiesTypical Bond Energies

C−O 358

CatenationCatenation

Since carbon can undergo Since carbon can undergo extensive catenation and make as extensive catenation and make as many as four bonds, the array of many as four bonds, the array of compounds is limitless.compounds is limitless.

The simplest compounds, those The simplest compounds, those with carbon and hydrogen, are used with carbon and hydrogen, are used as the basic structure of all as the basic structure of all molecules.molecules.

Carbon vs. SiliconCarbon vs. Silicon

Carbon vs. SiliconCarbon vs. Silicon

One of the clearest differences One of the clearest differences between the two elements is in their between the two elements is in their oxides. Carbon dioxide is a non-oxides. Carbon dioxide is a non-polar molecular substance with polar molecular substance with double bonds between the carbon double bonds between the carbon and the oxygens.and the oxygens.

O=C=OO=C=O:

:

::

Carbon vs. SiliconCarbon vs. Silicon

Since silicon doesn’t readily Since silicon doesn’t readily make double bonds, and the silicon-make double bonds, and the silicon-oxygen bond is so stable, the oxide oxygen bond is so stable, the oxide of silicon is a network solid, in which of silicon is a network solid, in which each silicon atom is bonded to four each silicon atom is bonded to four oxygen atoms which are, in turn, oxygen atoms which are, in turn, bonded to other silicon atoms. bonded to other silicon atoms.

Carbon vs. SiliconCarbon vs. Silicon

The oxide of The oxide of silicon is found in silicon is found in quartz and sand.quartz and sand.

SilicatesSilicates

Silicates, ions containing silicon Silicates, ions containing silicon and oxygen, are found in most rocks, and oxygen, are found in most rocks, soils and clays. Their structures also soils and clays. Their structures also are based on interconnected SiOare based on interconnected SiO44 tetrahedral units.tetrahedral units.

SilicatesSilicatesGlass Glass

contains contains silicates in a silicates in a more random more random pattern than pattern than found in quartz. found in quartz.

Group 5AGroup 5A

The elements of group 5A may form The elements of group 5A may form three, five or six covalent bonds, except three, five or six covalent bonds, except for nitrogen which cannot expand its for nitrogen which cannot expand its “octet.”“octet.”

Due to its small size, nitrogen readily Due to its small size, nitrogen readily forms forms ππ bonds. Thus elemental nitrogen, bonds. Thus elemental nitrogen, NN22, has a triple bond. The other elements , has a triple bond. The other elements exist as larger molecules containing exist as larger molecules containing single bonds.single bonds.

NitrogenNitrogen

Elemental nitrogen is an Elemental nitrogen is an extremely stable molecule due to the extremely stable molecule due to the triple bond. As a result, many triple bond. As a result, many nitrogen containing compounds nitrogen containing compounds decompose exothermically (and decompose exothermically (and sometimes explosively) to form sometimes explosively) to form nitrogen gas.nitrogen gas.

ExplosivesExplosives

Nitrogen based Nitrogen based explosives such as explosives such as nitroglycerin, will nitroglycerin, will rapidly decompose rapidly decompose when ignited or when ignited or exposed to a sudden exposed to a sudden impact.impact.

ExplosivesExplosives

4 C3H5(NO3)3(l) 6 N2(g) + 12 CO2(g) + 10 H2O(g) + O2(g) + energy

Note the large number of moles of gaseous products. Explosives typically involve a very large volume change, producing many moles of small gaseous molecules.

ExplosivesExplosives

Trinitrotoluene, TNT, is another nitrogen based explosive.

2C7H5(NO3)3(l) 12 CO2(g) + 5 H2(g) + 3N2(g) + 2C(s) + energy

Sodium AzideSodium Azide

Sodium Sodium azide, NaNazide, NaN33(s), is (s), is used in air bags used in air bags in automobiles. in automobiles. A small amount A small amount of sodium azide of sodium azide (100g) yields 56L (100g) yields 56L of nitrogen gas at of nitrogen gas at 2525ooC and 1 atm.C and 1 atm.

Sodium AzideSodium Azide

2 NaN2 NaN33((ss) ) 2Na( 2Na(ll) + 3 N) + 3 N22((gg))

This reaction takes place in about 40ms. This reaction takes place in about 40ms. Other components are put in the air bag Other components are put in the air bag so that the molten sodium metal is so that the molten sodium metal is deactivated into glassy silicates.deactivated into glassy silicates.

10 Na(10 Na(ll) +2KNO) +2KNO33((ss) ) KK22O(O(ss) +5Na) +5Na22O(O(ss)+ )+ NN22((gg))

2 K2 K22O(O(ss) + SiO) + SiO22((ss) ) K K44SiOSiO44((ss))

2 Na2 Na22O(O(ss) + SiO) + SiO22((ss) ) Na Na44SiOSiO44((ss))

Isolation of PhosphorusIsolation of Phosphorus

Phosphorus Phosphorus was initially was initially isolated in an isolated in an attempt to extract attempt to extract gold from urine.gold from urine.

The element The element emits light and emits light and glows when glows when exposed to exposed to oxygen.oxygen.

PhosphorusPhosphorus

Elemental phosphorus exists as Elemental phosphorus exists as several allotropes. All differ greatly several allotropes. All differ greatly in structure from nitrogen due to a in structure from nitrogen due to a lack of multiple bonding between the lack of multiple bonding between the larger phosphorus atoms. larger phosphorus atoms. Phosphorous can also use Phosphorous can also use dd orbitals orbitals to expand its bonding.to expand its bonding.

Elemental PhosphorusElemental Phosphorus

white

phosphorus

black

phosphorus

red

phosphorus

Elemental PhosphorusElemental Phosphorus

White PhosphorusWhite Phosphorus

White phosphorus White phosphorus exists as discrete Pexists as discrete P44 molecules. It is a molecules. It is a waxy white solid that waxy white solid that is very poisonous is very poisonous and reactive. It and reactive. It burns vigorously in burns vigorously in air, and is stored air, and is stored under water.under water.

White PhosphorusWhite Phosphorus

The element gets its name from The element gets its name from the phosphorescent glow emitted by the phosphorescent glow emitted by white phosphorus when it is exposed white phosphorus when it is exposed to air in the dark.to air in the dark.

White phosphorus has been White phosphorus has been used in weaponry. The pieces of used in weaponry. The pieces of phosphorus in bombs and grenades phosphorus in bombs and grenades get embedded in the skin, where get embedded in the skin, where they burn.they burn.

Red PhosphorusRed Phosphorus

Red Phosphorus is a polymeric chain of PRed Phosphorus is a polymeric chain of P44 units. It is stable in air to a temperature units. It is stable in air to a temperature of 400of 400ooC. Red phosphorus is used in C. Red phosphorus is used in “safety” matches on the striking surface.“safety” matches on the striking surface.

Red PhosphorusRed Phosphorus

Red phosphorus is used in “safety” Red phosphorus is used in “safety” matches on the striking surface.matches on the striking surface.

Black PhosphorusBlack Phosphorus

Black phosphorus is the most Black phosphorus is the most stable of the allotropes. It is formed stable of the allotropes. It is formed from white phosphorus that is from white phosphorus that is heated under very high pressures.heated under very high pressures.

OxygenOxygen

Oxygen contains a double bond Oxygen contains a double bond that is much stronger than a single that is much stronger than a single bond (494 kJ/mol vs. 142 kJ/mol). bond (494 kJ/mol vs. 142 kJ/mol). The lower elements in the group The lower elements in the group form much weaker form much weaker ππ bonds due to bonds due to their larger atomic size and greater their larger atomic size and greater bond length.bond length.

OxygenOxygen

Oxygen is a colorless, odorless Oxygen is a colorless, odorless gas that forms a pale blue liquid. gas that forms a pale blue liquid. The molecule is The molecule is paramagneticparamagnetic due to due to the presence of two unpaired the presence of two unpaired electrons, and is attracted to a electrons, and is attracted to a magnetic field.magnetic field.

OzoneOzone

Ozone, OOzone, O33, is an allotrope of , is an allotrope of oxygen. It occurs naturally in the oxygen. It occurs naturally in the upper atmosphere of earth. The upper atmosphere of earth. The ozone layerozone layer absorbs ultraviolet light absorbs ultraviolet light and serves to help screen out and serves to help screen out harmful, cancer causing, radiation.harmful, cancer causing, radiation.

SulfurSulfurSulfur is found Sulfur is found

in large deposits as in large deposits as the free element, the free element, or in a variety of or in a variety of ores. Elemental ores. Elemental sulfur has a variety sulfur has a variety of forms and of forms and structures. At structures. At room temperature, room temperature, the most stable the most stable form is rhombic form is rhombic sulfur, Ssulfur, S88 rings. rings.

Structure of SulfurStructure of Sulfur

Sulfur has a Sulfur has a tendency to bond tendency to bond with itself. This is with itself. This is called called catenationcatenation. . The sulfur-sulfur The sulfur-sulfur bonds are stable, bonds are stable, despite lone pairs, despite lone pairs, since the bond since the bond length is relatively length is relatively long.long.

SulfurSulfur

If molten sulfur is cooled slowly, If molten sulfur is cooled slowly, the eight- membered rings stack into the eight- membered rings stack into monoclinic sulfurmonoclinic sulfur, which has a , which has a needle-like appearance.needle-like appearance.