Atoms & Reactions

Last Minute Revsion For Module 1

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Atoms & Reactions
The Atom
Mass number (the top) = protons + neutrons Atomic number (the bottom) = protons.
Isotopes have the same chemical properties, due to same election configuration but different physical properties e.g.
densities due to a different mass.
Atomic Models
John Dalton ­ Solid spheres, different spheres made up different elements.
J J Thomson ­ Discovered `corpuscles' (electrons) and created the plum pudding model, a solid charged sphere with
negative electrons embedded into it.
Ernest Rutherford ­ Gold foil experiment ­ they fired alpha particles at a thin sheet of gold expecting them to be deflected
back from the plum pudding but most passed through with a small number deflected back. He created the nuclear model,
most of the atoms mass in the nucleus with a cloud of electrons and the rest empty space.
Modifications to Rutherford's model
o Henry Mosley ­ Discovered the charge increases from one element to another. So Rutherford investigated and
discovered the proton.
o Rutherford predicted there is one more element in the atom and James Chadwick discovered the neutron.
Bohr model ­ Explained noble gases.
o Electrons in fixed shells with a fixed energy.
o When a electron moves shells electromagnetic radiation is emitted or absorbed. This is a fixed frequency.
Relative Mass
Relative atomic mass ­ The average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12.
Relative isotopic mass ­ The average mass of an atom of an isotope on a scale where an atom of carbon-12 is exactly
12.
Calculating RAM ­ Multiply each relative isotopic mass by its % abundance and add up the results. Then divide by 100 (or
in a mass spectrum the sum of the relative abundances).
Relative molecular/formula mass ­ Add up the RAM.
The Mole
Number of moles = Number of particles you have ÷ Avogadro's constant
Number of moles = Mass of substance ÷ Molar mass
Concentration Calculations
Number of moles = Concentration X Volume (dm³)
Number of moles = Volume (dm³) ÷ 24
Formulas
Empirical formula ­ Simplified whole number ratio of atoms in a compound.
Molecular formula ­ Actual number of atoms in a molecule.
If you know the empirical formula and molecular mass you can work out the molecular formula...
o Find the empirical mass.
o Divide molecular mass by empirical mass to tell you the multiples.
o Multiply the empirical formula by the by that number.
Calculating Formulas
Calculating empirical formulas from experimental data. (if you get a % composition assume you have 100g)
o Work out the moles of each product made.
o Use the moles to work out how many moles of each atom you started with.
o Write a ratio of moles present at the start.
o Divide by the smallest number of moles for a whole number ratio.

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Balancing Equations
With ionic equations balance charges too (so add electrons (e-))
Equations and Calculations
Calculating masses
o Write out the balanced equation for the reaction.
o Work out how many moles of reactant you have.
o Use the molar ratio from the balanced equation to work out the number of moles of product formed.
o Calculate the mass of product using the moles.
Acids, Bases and Salts
Acids release H+ ions (proton donors).
Bases accept the H+ ions (proton accepter).…read more

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