Covalent Bonding - 4th Flashcards
1
Q
What happens when non-metal atoms bond?
A
- they share pairs of electrons to get a full outer-shell
2
Q
how can you work out which non-metals share electrons when they bond?
A
- by drawing arrows or using highlighters on the unpaired electrons on each atom
- an atom will make a shared pair for each electron missing from its outer shell
- e.g. N always shares 3 times and O always shares 2 times (how many electrons they need are how many bonds they make)
- once known how many they share, draw in its other electrons
3
Q
how many pairs of electrons can molecules have?
A
- some molecules contain double or triple pairs
4
Q
What happens when S and F share electrons?
A
- S has 6 in the outer shell - needs to share two pairs
- F has 7 in the outer-shell - needs to share one pair
- So we need 2 * F and 1*S
5
Q
what is covalent bonding?
A
- the electrostatic attraction between protons in two nuclei and a shared pair of electrons between them
- the shared pair of electrons effectively pull the nuclei of the atoms closer together
- very strong attraction
- a small group of atoms held together by covalent bonds is called a simple molecule.
6
Q
what are simple molecules?
A
- a small group of atoms held together by covalent bonds is called a simple molecule
- have strong covalent bonds
- weak intermolecular forces
7
Q
what happens when simple molecular substances boil?
A
- weak intermolecular forces break, not the bonds!!
8
Q
what is the relation between molecular mass and the strength of weak intermolecular forces?
A
- as molecular mass increases
- so does the strength of the weak intermolecular forces
- boiling point increases
9
Q
what does electrical conductivity require?
A
- charged particles that can move freely
10
Q
why can simple molecular substances never conduct electricity?
A
- electrical conductivity requires charged particles that can move freely, but in a simple molecular substance, there aren’t any charged particles
- they can never conduct electricity because molecules are neutral.
10
Q
What is C60 fullerene?
A
- a unique simple molecule composed of sixty carbon atoms in a ball
- low boiling point - not as low as other molecules - has a high molecular mass
-mm - 720 - bp - +600
- soft and slippery solid -> molecules can roll over each other easily
- electrical insulator - molecules are neutral
11
Q
what is diamond?
A
- form of pure carbon arranged into a giant lattice
- every C makes 4 covalent bonds
- tetrahedral shape
- strong, grid like arrangement
- sublimes (s->g) at v.h temperatures
- cannot conduct electricity -> no freely moving charged particles
- all atoms are neutral, and all electrons are stuck inside an atom/bond
12
Q
why does diamond sublime at very high temperatures?
A
- covalent bonds are very strong
- there are lots of bonds in the giant lattice
- lots of energy is required to break all the bonds
- therefor is one of the hardest substances -> used in cutting
13
Q
what is graphite?
A
- graphite is another form of pure carbon arranged into a different giant lattice
- layers of hexagons of C atoms
- every C makes 3 covalent bonds
- weak intermolecular forces between layers
- delocalised electrons inside each layer
- sublimes at v.h. temperatures
- soft and slippery because the layers can slide easily, so it used as a solid lubricant
- conducts electricity -> delocalised electrons that can move freely
14
Q
why does graphite sublime at very high temperatures?
A
- covalent bonds are very strong
- there are lots of bonds in the giant lattice
- lots of energy is required to break all the bonds
