Giant Covalent Substances

Chemical Bonding Brief Recap

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Substances

Metallic substances

Covalent Substances

Simple Molecular Substances

Ionic Compounds

Giant Molecular Substances 2

Giant Molecular Substances Macromolecules

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Giants -

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Giant metallic structure

Giant ionic structure

How about giant molecular structure? 4

Structure of Giant Molecular Substances (In general) • Giant covalent structure • Atoms held by strong covalent bonds

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Giant Molecular Substances

www.diamondvues.com/loose_diamond_shapes /

http://chemistry.about.com/od/periodictableelements/ig/Elem

mrbarlow.wordpress.com/2008/02/12/sandcastles

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Diamond

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Diamond

www.diamondvues.com/loos /

• Physical properties Melting/Boiling Point Hardness Electrical conductivity Solubility in water

Very high Very hard Does not conduct Insoluble

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Diamond • Structure: Giant covalent structure Carbon atoms Covalent bonds

http://www.uwgb.edu/dutchs/petrolgy/Diamond%20Structure.HTM

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Diamond • Structure: Giant covalent structure

Each carbon atom joined tetrahedrally to four other carbon atoms by strong covalent bonds. 10

Diamond Physical Properties Rationales Very high A lot of energy is required melting/boiling point to break the strong covalent bonds between Very hard the carbon atoms. Does not conduct electricity

No mobile charge carriers (ions or electrons) present.

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Diamond Uses Rationales Drill-tips and cutting tools It is very hard. Gemstones in jewellery –

http://www.supertoolscompany.com/F7948/diamond_cutting_tools.html http://www.jewelsdeparagon.com/catalog/product_info.php?produc

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Graphite

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Graphite

http://chemistry.about.com/od/periodictab

• Physical Properties Melting/Boiling Point Hardness Electrical conductivity Solubility in water

Very high Soft and slippery Conducts Insoluble

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Graphite • Structure: Giant covalent structure Microscopic image of graphite

Honeycomb

http://www.pbase.com/beekeeper/image/23669013 http://www.physik.uni-augsburg.de/exp6/imagegallery/afmimages/afmimages_e.shtml

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Graphite • Structure: Giant covalent structure Carbon atoms in one layer

Layers of carbon atoms

Covalent bonds Carbon atoms Van der Waals’ http://www.chemguide.co.uk/atoms/structures/giantcov.html forces

http://www.scifun.ed.ac.uk/card/flakes.html

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Graphite • Structure: Giant covalent structure • Consists of flat layers of carbon atoms • In each layer, each carbon atom joined to three other carbon atoms by strong covalent bonds. • Layers of carbon atoms are held by weak van der Waals’ forces. • No covalent bonds between the layers. 17

Graphite Physical Properties Very high melting/boiling point Soft and slippery

Conducts electricity

Rationales A lot of energy is required to break the strong covalent bonds between the carbon atoms within each layer. Layers of carbon atoms can slide over each other due to the weak van der Waals’ forces between the layers. Each carbon atom contributes one outer shell electron which is not used to form covalent bonds. These electrons can move along the layers to conduct electricity. 18

Graphite Uses Dry lubricant

Pencil lead Inert electrodes for electrolysis

Rationales It is slippery and does not decompose at high temperatures. It is soft as the carbon layers can flake off easily. It is a good conductor of electricity and is fairly unreactive.

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Diamond and Graphite • Different forms of carbon – Allotropes of carbon

Allotropes are different forms of the same element.

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Sand Silicon (IV) oxide/silicon dioxide/silica

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Sand • Physical properties Melting/Boiling Point Hardness Electrical conductivity Solubility in water

mrbarlow.wordpress.com/2008/02/12/sand

Very high Very hard Does not conduct Insoluble

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Sand • Structure: Giant covalent structure

http://www3.moe.edu.sg/edumall/tl/digital_resources/chemistry/images/img_CH_00019.jpg

Each silicon atom is covalently bonded to four oxygen atoms by strong covalent bonds in a tetrahedral structure and each 23 oxygen atom is covalently bonded to two silicon atoms.

Sand Physical Properties Rationales Very high A lot of energy is required melting/boiling point to break the strong Very hard covalent bonds between the carbon atoms. Does not conduct No mobile charge carriers electricity (ions or electrons) present.

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