Chemistry gcse paper 1 Flashcards
What do we use to measure atoms molecule and ions
We use moles as the actual masses are too small to be useful in calculations
One mole of a substance contains the same…….
Number of particle as one mole of any other substance
What is the Avogadro constant?
1 mole of a substance is the Avogadro number of particles of that substance
What is the Avogadro number?
6.02 x 10^23
Number of particles =
Avogadro x the amount of substance in a mol
Calculate the number of water molecule in 0.5 mol of water
6.02 x 10^23 x 0.5 = 3.01 x 10^23
Mass=
Relative formula mass x amount
Calculate the mass of 0.25 mol of carbon dioxide molecules ( Mr of co2=44)
44 x 0.25 = 11
How to calculate amounts in moles
Mass
Amount =———————————
relative atomic mass
What is a limiting reactant
The reactant used up first in a reaction
What does it mean when a product is in excess
The reactant left over when the limiting reactant is all used up
What is concentration measured in
G/ dm ^3. Or mol/dm^3
Concentration in mol/dm^3=
Amount of solute in mol
————————————
Volume in dm^3
In ionic bonds what do metal atoms and non metals atoms do
Metal atoms lost electrons to form positively charged ions
Non metal atoms gain electrons to form negatively charged ions
What is an ionic compound
A giant structure of ions
Why are lattices formed
The ions attract each other and form a regular pattern with positive charges ions next to each other
What is an ionic lattice held together by
Strong electrostatic forces of attraction between the positively charged ions
What is wrong with the 3D ionic lattice
It shows gaps which don’t actually exist
What does covalent bonding lead to
The formation of substances with different types of structures for example small molecules which contain a fixed number of atoms joined by covalent bonds
Giant covalent substances which contain many atoms joined by covalent bonds
What’s an example of a giant covalent
Silicon dioxide graphite and diamond
What are the properties of giant covalent structures
They have high melting points and boiling points this is because large amounts of energy are needed to overcome their sting covalent bonds to make them melt or boil. Most cannot conduct electricity as they have no charged particles free to move. Graphic a form of carbon however can conduct electricity.
How many strong covalent bond does each carbon atoms form in graphite and diamond
Diamond- each carbon atom is joined to 4 other carbon atoms
Graphite- forms 3 covalent bonds with other carbon atoms
Why does graphite conduct electricity
It has delocalised electrons like metals which can freely move between the layers in Graphite. Making graphite useful in batteries and electrolysis
Why is graphite a good lubricant
The forces between layer in graphite are weak so they can slide over each other making graphite slippery
