Ionic, covalent and metallic crystals 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
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 is diamonds purpose
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 can a metal be described as
A giant structure of positive ions surrounded by a sea of delocalised electrons
Why can metals conduct electricity
Because the delocalised electrons are free to move thought the structure
Why are metals malleable
Metals are usually easy to shape because their regular packing makes it simple for the atoms to slide over each other
Ionic bonding
A strong electrostatic attraction between oppositely charged ions
Why do ionic compounds have high melting and boiling points
Because of strong electrostatic forces between oppositely charged ions
Why do ionic compounds have high melting and boiling points
Because of the strong forces holding the lattices together
