2.1 - Atoms and Reactions
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Define the term isotope
Atoms of the same element which have the same number of protons but a different number of neutrons
Why are the reactions of isotopes the same?
Chemical reactions only involve electrons. Isotopes have the same number of electrons. Therefore, they have the same chemical reaction
What is the relative mass and relative charge of a proton, neutron and electron
Proton • Relative mass = 1 • Relative charge = 1 Neutron • Relative mass = 1 • Relative charge = 0 Electron • Relative mass = 1/2000 • Relative charge = -1
What never changes? The number of neutrons, the number of protons or the number of electrons?
Number of protons
Define relative isotopic mass
Mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
Define relative atomic mass
The weighted mean mass of an atom relative to 1/12th of the mass of an atom of carbon-12
How do you find the Mr of an element?
1) Multiply each relative isotopic mass by its relative isotope abundance and then add the result 2) Divide this result by the sum of the isotope abundances
When do we use the term relative molecular mass?
When referring to simple molecules
When do we use the term relative formula mass?
When we are referring to ionic or giant covalent molecules
List the ions formed by Group 1 - 7 elements (excluding group 4)
Group 1 = 1+ Group 2 = 2+ Group 3 = 3+ Group 5 = 3- Group 6 = 2- Group 7 = 1-
What should we do when trying to work out the formula for ionic compounds?
Balance out the charges
Define amount of substance
INSERT EXAM Q DEFINITION HERE
Given mass and Mr, what is the formula for moles?
n = m/Mr
Given moles and Mr, what is the formula for mass?
m = n x Mr
Given moles and mass, what is the formula for Mr?
Mr = m/n
What is the formula for Number of particles?
Number of particles = n x 6.02 x 1023
Given Avogadro’s constant and the number of particles, what is the formula for moles?
n = number of particles / 6.02 x 1023
Define empirical formula
The simplest whole number ratio of atoms of each element present in a compound
How do work out the empirical formula of a compound starting from its percentage composition?
1) Divide each percentage by its Mr 2) Divide each answer by whichever answer is the smallest 3) Find the lowest whole number ratio
How do you work out the empirical formula of a compound starting from its mass composition?
1) Divide each amount of grams by its atomic mass 2) Divide each answer by whichever answer is the smallest 3) Find the Lowest whole number ratio
What does anhydrous mean?
Without water
What does hydrated mean?
A crystalline compund containing water molecules E.g. CuSO4.5H2O
Define water of crystallisation
Water molecules that are combined into the crystalline structure of a hydrated compound
How do you find the water of crystallisation of a compound?
1) Work out the anhydrous mass 2) Calculate the amount of anhydrous salt (in moles) 3) Calculate the amount of water (in moles) 4) Divide the moles of anhydrous salt and moles of water smallest value of moles 5) Find the lowest whole number ratio