covalent yeah yeah yeah Flashcards
Substances with simple molecular structures are…
Gases or liquids, or solids with low melting points
Why do substances with simple molecular structures have low melting points?
It doesn’t take much heat energy to break the relatively weak intermolecular attractions
Substances with giant covalent structures have…
High melting and boiling points
Why do substances with giant covalent structures have high melting and boiling points?
Because you need a lot of heat energy to break the many strong covalent bonds.
A giant covalent structure is one with many atoms bonded together. To melt or boil them you are not separating intermolecular bonds (between molecules), you are separating intramolecular bonds that keep the molecule together. These bonds are strong covalent bonds which take a lot of energy to break, so a lot of heat energy is required before the bonds will break to boil or melt; meaning they have high melting and boiling points.
Describe the positions of the atoms in a diamond
In diamond, each carbon bonds strongly to four other carbon atoms in a tetrahedral arrangement. It is a giant covalent structure - it carries on and on in three dimensions. It is not a molecule as the number of atoms joined up in a real diamond is completely variable- depending on the size of the crystal
What are diamonds used for
Saw blades can be tipped with diamonds in high speed cutting tools used in stone and concrete
Why are diamonds used to tip high speed cutting tools
Diamond is very hard because of the very strong carbon - carbon covalent bonds, which extend throughout the structure in three dimensions.
Describe the positions of the atoms in graphite
Graphite has a giant layered structure, rather like a pack of cards. In a pack of cards. Each card is strong but the individual cards are easily separated. The same is true in graphs. The gaps between the layers are much bigger than the distances between the atoms in the layers.
What is covalent bonding
A strong attraction between the bonding pair of electrons and the nuclei of the atoms involved with the bond
Why does graphite structure make it useful
Graphite is a soft material with a slimy feel Although the forces holding the atoms together in each layer are very strong, the attractions between the layers are much seeker. Layers can easily be flaked off. Pure graphite is so slippery that it is used as a lubricant - eg powdered graphite is used to lubricate locks.
what is the formation of a covalent bond
the sharing of a pair of electrons between two atoms
