F321: Atoms And Reactions

Just a brief overview and introduction.

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Atomic Structure

Atoms consist of a nucleus made up of positive protons and neutral neutrons and electrons orbiting the nucleus in shells.
-Isotopes are atoms of the same element with different numbers of electrons.
-Atomic number is the number of protons in the nucleus of atoms.
-Mass number is the number of particles in the nucleus.  

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Atomic Masses

-Relative atomic mass is the weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.

-Relative isotopic mass is the mass of an atom of an isotope compared with with one-twefth the mass of an atom of carbon-12.

-Relative molecular mass is the weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12.

-Relative formula mass is the weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12.

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Amount Of Substances

-The amount of substance is the quantity whose unit in the mole, it's based on the Avogardo constant (NA), whoich is the numver of atoms per mole of the carbon-12 istope (6.02x10^23).

-A mole is the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12 isotope.

-Molar mass, M, is the mass per mole of a substance, whose units are g mol-1.

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Types Of Formula

-The empirical formula is the simplest whole-number ratio of atoms of each element present in a compound; these are always used for giant structures such as NaCl or SiO2.
-You find the molar ratio of atoms by using the equation, n=mass/molar mass, then dividing by the smallest number.
E.g. Mg moles = 0.025, Br moles = 0.050 -> 1:2 -> MgBr2

-The molecular formula is the actual numver of atoms in each element in a molecule.
-To find the molecular formula, it is necessary to find the empirical and then use the given Mr to deduce the amount of each element present. 

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Moles

-Molar volume is the volume per mole of a gas (dm3 mol-1), at RTP this is 24.0.
n=Volume (dm3)/24 

-The concentration of a solution is the amount of solute, in mol, dissolved per 1 dm3.
n=Concentration x Volume (dm3) 

-A standard solution is a solution of known concentration, normally used in titrations to determine unknown information about another substance.

-Stoichiometry is the molar relationship between the relative quantities of substances taking part in a reaction.

n=mass/molar mass 


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Acids And Bases

Acids (pH <7)
(E.g. Sulfuric [H2SO4], Hydrochloric [HCl], and Nitric [HNO3].
-When acid is added to water, the acid releases H+ ions, it is a proton donor.

Bases
-Common bases are metal oxides and hydroxides - NaOH (m.o.), MgO (hy.), these are proton acceptors.

Alkalis (pH >7)
(E.g. Sodium Hydroxide [NaOH], Potassium Hydroxide [KOH], and Ammonia [NH3].
-A special type of base that dissolves in water to form hydroxide ions, OH-.
(NaOH + aq -> Na+ + OH-) 

 

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Salts

-A salt is any compound formed from an acid when a H+ is replaced by a metal ion.
(E.g. HCl -> Chloride salts)

-They can be produced by neutralising acids with:
.Carbohydrates (2HCl + CaCO3 -> CaCl2 + H2O + CO2)
.Bases (2HCl + CaCO -> CaCl2 + H2O)
.Alkalis (HCl + NaOH -> NaCl + H2O)


 

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Water Of Crystalisation

-Hydrated refers to a crystalline compound containing water molecules.
-Anhydrous refers to a substance containing no water molecules.

-Water of crystalisation refers to water molecules that form an essentail part of the crystalline structure of a compound. (E.g CuSO4 . 5H2O)
-The relative number of water molecules is shown after the seperating dot. 

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Oxidation Number

-An oxidation number is a measure of the number of electrons that an atom uses to bond with atoms of another element. Here are some rules:
-Uncombined element = 0
-Combined oxygen = -2
-Combine hydrogen = +1
-Simple ion = charge on ion
-The roman numeral (E.g. V = 5) refers to the oxidation number on some transition metals or compounds. 

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Redox Reactions

-Oxidation is loss of electrons or an increase in oxidation number.
-Reduction is gaining of electrons or a decrease in oxidation number.
-A redox reaction is a reaction in which both take place. 
-Furthermore a reducing agent adds electrons and reduces, whereas an oxidising agent takes electrons from and oxidises another species.

A good summary of this is OILRIG, Oxidation is loss, Reduction is gaining (of electrons). 

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