CHEM unit 1

1.1

DEFINITIONS -

-atomic number - number of protons in the nucleus of an atom

-mass number - number of protons and the neutrons in the nucleus

-isotopes - atoms of the same element with the same number of protons but different number of neutrons

-relative atomic mass (Ar) - the average mass of an element relative to the 12th mass of carbon 12

-relative isotopic mass - the mass on one isotope relative to the 12th mass of carbon 12

-relative molecular mass - the sum of all the relative atomic masses of its consituent atoms

-molar mass - the mass of one mole of substance

-1st ionisation energy - the amount of energy required per mole to REMOVE one electron from each gaseous atom to form a singly positive ion

-1st electron affinity - the energy change per mole for the ADDITION of one electron to a gaseous atom to form a singly negative ion

MASS SPECTROMETRY

-VAPORISATION

the sample is turned into gas using an electrical heater

-IONISATION

the gas particles are bombarded with high enery electrons to ionise them, electrons are knocked off the particles leaving positive ions, most of the positive ions formed carry a charge of +1 because it is much more difficult to remove further electrons from an already positive ion

-ACCELERATED

the positive ions are accelerated by an electric field

-DEFLECTION

the different ions are deflected by the magnetic field by different amounts

-DETECTION

as the magnetic field is slowly increased different ions with a higher mass/charge can reach the detector (stream b) and a mass spectra is produced

the more ions arriving the greater the current

ELECTRONIC STRUCTURE

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4d10 4f14

SIZE OF ATOMS AND IONS

-atoms get smaller going across a period LEFT - RIGHT because the nucleur charge increases pulling the electrons in closer though the number of shells is the same

-atoms get bigger going down a group because there are more shells of electrons

-a positive ion is smaller then the neutral atom from which it was made, because the ion has one shell fewer then the atom

-a negative ion is bigger then the neutral ion because the extra repulsion between electrons causes them to spread out

1ST IONISATION ENERGY

-the general trend is increase going from left to right across a period due to an increased nucleur charge (atomic number) without an increase in the number of inner shielding electrons

-GROUP 3 - it is easier to remove an electron from the higher energy p orbital (decreases ionisation energy)

-GROUP 6 - the repulsion of the two electrons in the p orbital makes it easier to remove one of them

-there is a DECREASE GOING DOWN…