AS Physical Flashcards
Isotope
-Atoms with the same number of protons, but different number of neutrons.
-Isotopes have similar chemical properties because of the same electronic structure.
-They may have slightly varying physical properties because they have different masses.
Four sub-shells
-S- max 2
-P- max 6
-D- max 10
-F- max 14
First ionisation energy
The first ionisation energy is the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge.
Second ionisation energy
The second ionisation energy is the enthalpy change when one mole of gaseous ions with a positive charge forms one mole of gaseous ions with a double positive charge.
Factors affecting ionisation energy
-Attraction of the nucleus (protons)
-The distance of the electrons from the nucleus (bigger atom- weaker attraction)
-Shielding of the attraction of the nucleus (weakened attraction)
4 stages of mass spectrometry:
-Ionisation
-Acceleration
-Flight tube
-Detection
Ionisation
Two ways:
-Electron impact.
-Electrospray ionisation.
Electron impact
-A vapourised sample is injected at low pressure.
-An electron gun fires high energy electrons at the sample.
-Knocks out an outer shell electron.
-Forming positive ions with different charges.
(Used for elements and substances with low formula mass and fragments them).
Electrospray ionisation
-The sample is dissolved in a volatile, polar solvent.
-Injected through a fine hypodermic needle creating a fine mist or aerosol.
-Tip of the needle has high voltage.
-At the tip of the needle, the sample molecules, M, gains a proton, H+, from the solvent forming MH+
-M(g)+H+ –> MH+(g)
-The solvent evaporates away while the MH+ ions move towards a negative plate.
Acceleration
-Positive ions are accelerated by an electric field.
-To a constant kinetic energy (KE=1/2xmxv^2).
Flight tube
-The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster.
-The heavier particles will take longer to move through the drift area.
-The ions are distinguished by different flight times.
Detection
-Ions reach detector and generate a small current, which is fed into a computer for analysis.
-Current is produced by electrons transferring from the detector to the positive ions.
-Size of the current is proportional to the abundance of the species.
-For each isotope the mass spectrometer can measure a m/z (mass/charge ratio) and abundance.
Relative atomic mass
The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.
Relative molecular mass
The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.
Avogadro constant
There are 6.022 x 10^23 atoms in 12 grams of carbon-12.
Mole
The amount of substance in grams that has the same number of particles as there are in atoms in 12 grams of carbon-12.
Concentration
Ideal gas equation
PV=nRT
Pressure(Pa) x Volume(m^3)= No. of moles x Gas constant x Temperature(K)
Empirical formula
An empirical formula is the simplest ratio of atoms of each element in the compound.
Molecular formula
A molecular formula is the actual number of atoms of each element in the compound.
Atom economy and equation
-Found directly from the balanced equation.
-Theoretical.
-Mass of desired product/ total mass of reactants x 100
-High atom economy- maximum mass of reactants ends up in the desired product.
Percentage yield
-Actual yield/ Theoretical yield x 100
-High yield- efficient conversion of products to reactants.
Ionic bonding
The electrostatic force of attraction between oppositely charged ions formed by electron transfer.
Metals in ionic bonding
Metals lose electrons and form positive ions.
Non-metals in ionic bonding
Non-metals gain electrons and form negative electrons.
Ionic bonding strength
Bonding is stronger and melting point is higher when the ions are smaller and have higher charges.
Ionic radii
-Positive ions are smaller as they have one less shell and higher ratio of protons- increased strength holding ion closer together.
-Negative ions are bigger as they have one more shell but same number of protons- attraction is less making ion bigger.
Properties of ionically bonded compounds
-Melting and boiling points- high because of high electrostatic forces of attraction between oppositely charged electrons.
-Solubility in water- generally good.
-Conductivity when solid- poor, ions can’t move, fixed in lattice.
-Conductivity when molten- good, ions can move.
-General description- crystalline solids.
Covalent bonding
A shared pair of electrons.
Coordinate bonding
-When the shared pair of electrons in a covalent bond come from only one of the bonding atoms. Also known as dative bond.
-Common examples: NH4+, H3O+, NH3BF3.
-Direction of arrow goes from the atom that is providing the lone pair to the atom that is deficient.
Properties of simple covalently bonded compounds
-Melting and boiling points- low, weak IMF.
-Solubility in water- generally poor.
-Conductivity when solid- poor, no ions to conduct and electrons are localised.
-Conductivity when molten- poor, no ions.
-General description- mostly gases and liquids.
Properties of macromolecular covalently bonded compounds
-Melting and boiling points- high, strong covalent bonds in macromolecule structure.
-Solubility in water- insoluble.
-Conductivity when solid- some are, electrons can’t move but some have delocalised electrons.
-Conductivity when molten- poor.
-General description- solids.
Metallic bonding
The electrostatic force of attraction between the positive metal ions and delocalised electrons.