Chemistry - Friday 8th April Flashcards
What is the definition of an ionic bond?
The ionic bond is the electrostatic attraction between the negative non-metal ion and the positive metal ion.
Describe the structure of ionic compounds.
An ionic compound is a giant lattice, with the forces of the ionic bonds going in all directions.
What are the key characteristics of ionic compounds.
High BP/MP because of the large amounts of energy needed to break the many strong ionic bonds.
Ionic compounds can only conduct if molten or dissolved as in these forms the charged ions are able to move and carry current.
What is the definition of a covalent bond?
The electrostatic attraction between the negative shared pair of electrons and the positive nuclei of the non-metal covalent atoms.
What are the key characteristics of simple covalent molecules?
Low MP/BP because little energy is needed to overcome the weak intermolecular forces between molecules when melting or boiling.
The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points. (This is how fractional distillation of crude oil works).
Cannot conduct as there are no charged particles free to move
Can covalent molecules conduct?
No, because there are no charged particles free to move.
Can giant covalent structures conduct?
Diamond cannot conduct.
Graphite and Fullerenes can conduct, because they have delocalised electrons that are free to move and carry current/heat.
Do covalent molecules have high or low melting/boiling points?
Low MP/BP
Little energy is needed to overcome the weak intermolecular forces between molecules when melting or boiling.
The strength of the intermolecular forces depends on the size of the molecule. The bigger the molecule, the stronger the intermolecular forces, and the higher the MP/BP. This is why alkanes of different sizes boiling at different points so they are separated by fractional distillation. Larger alkanes = Stronger IMF = Higher BP.
Describe the structure of diamond, and how this results in its characteristics.
Giant covalent structure
Carbon atoms only
Each Carbon bonds to 4 other Carbons
No delocalised electrons - cannot conduct
Tetrahedral structure with many strong covalent bonds
Strong and rigid
High MP/BP
Describe the structure of graphite, and how this results in its characteristics.
Giant covalent structure
Carbon atoms only
Each Carbon bonds to 3 other Carbons
Forms layers of hexagons
1x delocalised electron per Carbon atom because each Carbon only bonds with 3 other Carbons, leaving one electron unpaired. These electrons are free to move and carry charge/current within the layer. Thus, graphite can conduct
Weak intermolecular forces between the layers so the layers can slide over each other. Therefore, Graphite is soft and slippery
Describe the structure of fullerenes, and how this results in its characteristics.
Carbon atoms only
Each Carbon bonds to 3 other Carbons forming hollow spheres
Delocalised electrons free to move within the sphere so it can conduct
What is the definition of a metallic bond?
The electrostatic attraction between the negative sea of delocalised electrons and the positive metal ions.
Describe the structure of metals.
Metals consist of giant structures of atoms arranged in a regular pattern. The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure.
Describe the characteristic properties of metals.
Metals are good conductors of electricity and heat because the delocalised electrons in the metal can move throughout the metal and carry electrical charge.
Metals have a higher MP and BP due to the metallic bonds being strong and needing a lot of energy to be overcome.
What are alloys?
In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped. This is because the regular layers can slide over each other.
These pure metals are too soft for many uses and so are mixed with other metals making alloys, which are harder.
