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Formulae, equations and amounts of substances (1.1)
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Mapa Mental sobre Formulae, equations and amounts of substances (1.1), criado por josh bart em 23-03-2014.
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Formulae, equations and amounts of substances (1.1)
Foundations of Chemistry
Atoms
A greek word meaning indivisable
Structure
Composes of elctron shells and a nucleus
Nucleus contains protons with a + charge, and neutrons with no charge
Elctron shell contain elctrons which have no charge
Atoms of a element consist of the same amount of protons
An element cannot be broken down chemicallly into simpler substances
Isotopes
Atoms with the same atomic No. but different No. of neutrons are known as isotopes
The varying No. of neutrons makes the mass of the atoms also vary
Isotopes of a element have smae chemical propertise but different masses
This can make some isotopes radioactive
Formulea and equations
Holding atoms together
Ionic bonding
Between non-metals and metals
Atoms lose or gain electrons to gain stable, full outer shells
Metal atoms lose elctrons
Non-metals gain electrons
Strong fources of atraction (ionic bonds) hold opositly charged ions together in giant ionic latice structures
Covalent bonding
Only between non-metals
Atoms share elctrons and this is what holds them together, large covalent latice structure
Ionic half equations
You only have to spli up molocules into the seperate ions if they are in an aqueose state in the reaction
Shows exactly whats happening in an equation
Molecular equation
Gives a complete description of all reactants
Size/wheight of atoms
Relative atomic mass (RAM)
Is a relative scale compared to the mass of a single standard atom of carbon-12
represented by the symbol Ar
Defined as the average mas of a elements isotopes compared with the mass of an atom of carbon-12
Mixtures of isotopes
The RAM of every element is an average which reflects the mix of isotopes abd their differing masses within the elemnt
Most elements have one major isotope and small proportions of others
Moles
Defined as the amount of substance that contains as many particles (atoms, ions or molecules) as there are atoms in exactly 12g of carbon 12
moles is abreviated to mol
No. moles = mass(g) / molar mass (gmol-1)
Molar mass is just a numerical value of RAM
Tells you the No. of grams of that substance that is needed to make up one mole of that substance
You can 'x' the moles of an element by the avagadro constant to find out the amount of atoms in a cirtain mass
Avagadro constant = 6.02*10**23
Using moles
Relative molecular mass (Mr) is the mass of a molecule
The realative formulae mass is used for the mass of ionic compunds
Molar volume
one mole of any gas must ocupy the same volume under the same conditions
This is one of the major implications of avagardros law
Standard conditions are 1 atmosphere (atm) and 298k or 25 degrees celcius
Gases ocupie a volume of 24dm**3
Calculating formulae using moles
Empirical formula
This is the simplest ratio that the atoms of a compound can be in
The formula of a compound gives the ratio of different atoms present
Molecular formula
Tells you how many atoms of the elments in one mole of a compund are bound together
The empirical formula dose not tell you this
Sometimes the empirical and molecular formula can be the same
Giant structures of atoms nd ions are described by their epirical fromula not molecular
Measuring concentration
Moles in solution
A solute is a solid, liquid or gas dissolved in a solvent
Concentration is measured in moles per cubic decimeter (mol dm**3)
i decimeter is equivilent to 1000cm cubed
Concentration (molarity) = moles of solute / volume of solution (dm**3)
More units of concentration
% by mass
For use as a quick comparison
% by mass = mass of solute / mass of solution * 100
% by volume
For when you have a mixture of two liquids or two gases
% by volume = volume of one component / Total volume * 100
Parts per million (PPM)
Usefull for when there is very low concentrations involved
Concentration = Mass of component / mass of solution * 1000000
Yeilds and atom economy
The yeild of a reaction
This is the % of a product that you recieve from the reaction between two reactants
If the smae mass of reactants reacts to form the same mass of products, then the yeild from the reaction is said to be 100%
This cannot always be achieved and is very rare in most cases, usually due to cirtain factors
The reactants may not be pure
not all reactants will be used up because it is an equilibrrium reaction
Products may be left behind on apparatus
There is always a degree of human error
Atom economy
Developed by Professor Barry Trost
His idea was that it was not the overall yield, but the No. of reacting atoms that ended up in product that mattered
Atom Econ (%) = Mass of desired atoms in product / Total mass of atoms * 100
Have to use Relative.F.M
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