Atomic Structure And Isotopes Flashcards
What is valency?
The number of bonds an atom can form
What is the cross over rule?
When the charges of two ions are crossed to find a compound
E.g. Mg2+ Br-
MgBr2
What is an ion?
An electrically-charged particle, formed by the loss or gain of electrons.
What is an isotope?
An atom of the same elements with the same number of proteins and electrons but a different number of protons.
What is relative atomic mass?
The weighted mean mass of an atom of an element relative to the 1/12th of the mass of an atom of carbon 12.
What is the relative isotopic mass?
Mass of an isotope relative to the 1/12th of the mass of an atom of carbon 12.
Why are the chemical properties of an atoms isotopes the same?
Because there is the same number of electrons and the electrons control the reactivity.
Relative atomic mass equation.
Sum of isotopic masses/Sum of abundances.
Isotopic mass equation
Isotopic mass x abundance
What is empirical formula?
Simplest whole number ratio of atoms of each element present in a compound.
What is molecular formula?
The actual number and type of atoms of each element present in a molecule.
How to work out empirical formula?
1) Write down relevant information
2) Convert masses to moles
3) Divide moles by smallest mole number
4) Use this number as little number
What does anhydrous mean?
No water of crystallisation
What does hydrous mean
With water of crystallisation
What is water of crystallisation
There are water molecules locked into lattice structure.
What is Avagadro’s number?
6.02x10^23
Mole equation 1 (particles)
n=no. of particles/avagadro’s number
Moles equation 2 (mass)
n=moles/molar mass
What is molar mass equivalent to?
Relative formula mass
What is stoichiometry?
The relationship between amount of reactant and product in the form of a balance equation.
How to work out mass of a product from given mass
1) Write balance equation
2) Work out moles of known mass
3) Work our moles of unknown using reacting ratio
4) Find mass with m=nxMr
Mole equation 3 (gas)
n=volume of gas/24
How do you convert from cm3 to dm3?
Divide by 1000 and vice versa.
What is the empirical formula practical?
Weigh crucible and lid
Add magnesium ribbon (coiled) and weigh again
Heat magnesium ribbon with lid until the reaction is almost complete (stop burning bright orange)
Then, remove the lid and heat for further 5 minutes.
Tap magnesium oxide when you do this
Re weigh crucible
Calculate empirical formula
How to work out molecular formula
1) Work our molecular mass of your calculated empirical formula
2) Divide your Mr by the one given in the question
3) Multiply your empirical formula by the answer given in division to get molecular formula.
How to calculate percentage yield?
% yield = experimented yield/theoretical yield x100
How to calculate water of crystallisation
1) Calculate mass of water lost
2) Calculate moles of anhydrous salt
3) Use mass of water lost to calculate moles of water
4) Divide moles by smallest mole number
5) Use this as big numbers in front
How to improve atom economy?
- Find an alternative reaction
- Find a use for waste products
How to calculate empirical formula if you’re given percentages?
Treat percentages as masses
What is the ideal gas equation?
PV=nRT
What are the assumptions for an ideal gas?
- Random motion
- Elastic collision
- Negligible size
- No intermolecular forces
Under what conditions are gases likely to behave most like an idea gas?
- Low pressure
- High temperature
Why do gases behave most like an ideal gas at low pressure and high temperature?
- At low pressure, size of particles compared to the volume is negligible
- At high temperatures, particles move so fast that the chance of intermolecular forces forming is small
What are the units for the ideal gas equation?
P in Pa
V in m^3
T in K
R in Jmol^-1
How to convert from degrees celcius to kelvin?
+273
Why does the Harber Process have an atom economy of 100%?
Because there is only one product, NH3
Why is a high atom economy good?
- Reduces production of unwanted products
- Makes process more sustainable by removing waste products
