Covalent Bonding - 4th Flashcards
What happens when non-metal atoms bond?
- they share pairs of electrons to get a full outer-shell
how can you work out which non-metals share electrons when they bond?
- 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
how many pairs of electrons can molecules have?
- some molecules contain double or triple pairs
What happens when S and F share electrons?
- 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
what is covalent bonding?
- 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.
what are simple molecules?
- a small group of atoms held together by covalent bonds is called a simple molecule
- have strong covalent bonds
- weak intermolecular forces
what happens when simple molecular substances boil?
- weak intermolecular forces break, not the bonds!!
what is the relation between molecular mass and the strength of weak intermolecular forces?
- as molecular mass increases
- so does the strength of the weak intermolecular forces
- boiling point increases
what does electrical conductivity require?
- charged particles that can move freely
why can simple molecular substances never conduct electricity?
- 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.
What is C60 fullerene?
- 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
what is diamond?
- 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
why does diamond sublime at very high temperatures?
- 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
what is graphite?
- 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
why does graphite sublime at very high temperatures?
- covalent bonds are very strong
- there are lots of bonds in the giant lattice
- lots of energy is required to break all the bonds
what is silicon dioxide?
- also known as silica
- giant covalent structure
- every Si makes 4 covalent bonds
- every O makes 2 covalent bonds
- tetrahedral shape (like diamond)
- strong, grid-like arrangement.
- similar properties to diamond due to similar bonding and structure
- much less expensive -> less rare
what is the bonding, structure, essential properties and other properties of a metal + non-metal?
- ionic
- giant lattice
- high MP/BP, insulator when (s), conductor when (l) and (aq)
- brittle, usually soluble in water, crystalline
what is the bonding, structure, essential properties and other properties of only non-metals?
- covalent
- simple molecules
- low MP/BP, insulator
- usually insoluble in water, dull
what is the bonding, structure, essential properties and other properties of only metals?
- metallic
- giant lattice
- high MP/BP, conductor
- malleable, ductile, shiny
