Structure and Properties Flashcards
Why do solid ionic compound have high melting and boiling points?
- They have giant structures in which there are many strong electrostatic forces holding the ions together
- A lot of energy is needed to overcomethe ionic bonds to melt the solids
- Therefore they have high melting and boiling points and are solid at room temperature
Why can ionic substances conduct electricity when molten or when dissolved in water?
Because the ions are free to move and therefore able to carry an electrical charge
Why can some ionic compounds dissolve in water?
Because the water molecules can split up the lattice
What type of bond holds together molecules?
Covalent bonds
What are the properties of simple molecules?
- Low melting and boiling points
- No overall charge, therefore…
- Cannot carry an electrical charge
- Little attraction to each other
What causes the properties of simple molecules?
Weak intermolecular forces
Why are substances with large molecules more likely to be liquids or solids at room temperature?
The intermolecular forces are greater for larger molecules
What are macromolecules?
Giant covalent structures:
Huge, 3D networks of covalently bonded atoms
Why do substances with giant covalent structures have very high melting points?
Every atom is joined to several others by strong covalent bonds
These bonds require a large amount of energy to be broken, therefore the structures have high melting/boiling points
Describe the structure of diamond and what properties this gives it
- Regular, 3D giant structure
- Every atom covalently bonded to 4 others
- Makes it hard
- And transparent…
Silicon dioxide (silica) has a similar structure
Describe the structure of graphite and what properties this gives it
- Atoms are covalently bonded to 3 others
- Formed of giant, flat 2D layers of hexagons
- Weak intermolecular forces between layers
- So they can slide over each other
- This makes graphite slippery
- …and grey
- It can also conduct electricity
- This is due to the one delocalised electron per atom
What are fullerenes?
Large molecules formed from hexagonal rings of carbon atoms.
The rings join together to form cage-like structures
What are some of the uses of fullerenes?
- Drug delivery into the body
- Lubricants
- Catalysts
- Reinforcing metals
Describe the structure of metals and what properties/uses this gives them
- Arranged in layers
- When a force is applied these layers can slide past each other
- Can move into a new shape without breaking apart, so the metal bends and stretches into a new shape
- This means they are useful for making wires, rods, and sheet materials
- They have a delocalised electron cloud/sea
- This makes them good conductors of heat + electricity because the electrons move throughout the giant lattice and transfer energy quickly
What are the properties of alloys and what causes them?
- Alloys are mixtures of metals or metals mixed with other elements
- The different sized atoms in the mixture distort the layers in the metal structure
- This makes it more difficult for the layers to slide over each other
- This makes alloys harder than pure metals
What are thermosoftening polymers?
- Made up of lots of individual polymer chains tangled together
- Weak intermolecular forces between chains
- When heated they become soft as these forces are broken
- They harden again when they cool as forces bring the molecules back together again
- This means they can be remoulded by heating
Like spaghetti!
What are thermosetting polymers?
- Do not melt or soften when heated
- Set hard when first moulded due to strong covalent bonds which form cross-links between polymer chains
- These strong bonds hold the chains in position
Like twigs!
