Zusammenfassung der Ressource
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