Covalent substances-simple molecular
- Atoms form STRONG covalent bonds to form SMALL MOLECULES of several atoms
- But... forces of attraction between these molecules are WEAK
- So...melting and boiling points are low because molecules are easily parted.
- Most molecular substances are gasses or liquids at room temperature
- They dont conduct electricity because...no ions so no charge
- All atoms bonded by STRONG COVALENT BONDS... so high melting and boiling points
- Don't conduct electricity
- Each C forms 4 covalent bonds in a rigid structure
- Structure makes diamond the HARDEST natural substance
- PRETTY AND SPARKLY
- Each C forms 3 covalent bonds. Creates layers, free to move over each other (weak intermolecular forces can be rubbed onto paper)
- Soft and Slippery
- Non-metal...but, good conductor of heat and electricity. Each C atom has 1 delocalised electron (these conduct electricity)
- Silicon Dioxide:
- What sand is made of
- Each grain of sand is 1 giant structure of silicon and O2
- Metals consist of a giant structure.
- Metalic bonds involve "free electrons" which come from the outer shell of EVERY metal atom in the structure. These are free to move, so conduct heat and electricity.
- The electrons hold the atoms together in a REGULAR STRUCTURE. There are strong forces of electrostatic attraction between positive metal ions and the negative electrons. They allow layers of atoms to slide over each other, allowing metals to be BENT AND SHAPED.
- Smart materials behave differently depending on conditions.
- Eg: Nitinol "shape memory alloy"
- Tiny (1-100 nm)
- Contain roughly a FEW HUNDRED ATOMS.
- A nanoparticle has very different properties from its original chemical.
- Huge SA:V ratio.....help make new industrial catalysts.
- Used to make highly specific sensors.
- Nanotubes used to make stronger; lighter building materials.
- New cosmetics Eg: sun cream have been made using nanoparticles...as they don't leave white marks on the skin.
- Nanomedicine is absorbed more easily.
- Nanotubes conduct electricity so they can be used in tiny electric circuits for computer chips.
Relative Formula Mass
Relative Atomic Mass-top number in symbol square (mass number)
Relative Formula Mass-add up relative atomic masses in compound.
"ONE MOLE" IS RELATIVE FOLMULA MASS IN g
NUMBER OF MOLES=MASS IN G/RELATIVE FORMULA MASS
Percentage mass of an element in a compund = relative atomic mass *number of atoms/relative formula mass of compound*100 look at pg.96 of AQA
Masses in reaction-pg.98
- Always between 0-100%
- Percentage yield = actual yield/predicted yield*100
Why yields can't be 100%:
- The reaction is reversible so the product can react to produce the original reactants.
- Filtration-some lost in separation.
- Unexpected reactions
- Making sure we don't use resources up quicker than they can be replaced...there needs to be enough for future generations too!
Artificial colours can be separated using CHROMATOGRAPHY (pg 102 of AQA)
Machines can analyse unknown substances...
- They're sensitive-can detect tiny amounts
- Very fast-tests can be automated
- Very accurate
GAS CHROMATOGRAPHY can identify substances as it can separate out a mixture of compounds, and help identify substances present (pg 103 of AQA)
- What do mass number and atomic number represent?
- What is a compound?
- Describe the process of ionic bonding?
- What is covalent bonding?
- 3 properties of metals?
- Why are alloys harder than pure metals?
- Give an example of a "smart material"?
- Define Relative Atomic Mass?
- What are nanoparticles?
- What is the link between moles and relative formula mass?
- What mass of sodium is needed to rpoduce 108.2g of Sodium Oxide?
- 3 factors that reduce percentage yield?