ATOMIC STRUCTURE PART 2

TOF KEY EQUATION

mass= Ar÷Avogadro

mass spectrum

a type of chart produced by a mass spectrometer that shows information about the sample

if the sample is an element

each line represents the isotopes. Y-axis gives % abundance of ions. X-axis gives mass/charge ratio

mass spectrums from electrospray ionisation, each peak would be 1 unit greater than the actual relative mass of each

because a H+ has been added to for the +1 ion, the mass/charge ratio of isotope

mass spectrums from electron impact ionisation, each peak is the same as the relative mass of each isotope

because an electron has been knocked off to form +1 ions. the mass/charge ration of

calculating relative atomic mass

• for each peak, read the % from the y-axis and multiply it with the Mass/charge ratio

• add up these totals

• divide by 100

electron shells have principal quantum numbers

the further a shell is from the nucleus the higher its energy and the larger its principal quantum number

electron configuration 3 rules

• electrons fill up the lowest energy sub-shell first

• electrons fill up orbitals in a sub-shell singly before they start sharing

• for the configuration of ions from the S and P blocks of the periodic table, just add or remove electrons to or from the highest occupied sub-shell

chromium electron configuration

1s² 2s² 2p^{6 3}3s² 3p⁶ 3d⁵ 4s¹

copper electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

s block elements

can easily lose 1 or 2 electrons to form a positive ion with an inert gas configuration (full outer shell)

p block elements

can gain 1,2 or 3 electrons to form a negative ion with an inert gas configuration (full outer shell)

groups 4 to 7

can also share electrons when they form covalent bonds

first ionisation energy

the energy needed to remove 1 mole of electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

ionisation energies important points

• must always use the gas symbol

• always refer to 1 mole of atoms

• the lower the ionisation energy the easier it is to form a positive ion

factors affecting ionisation energy

• nuclear charge

• distance from nucleus

• shielding

nuclear charge

the more protons there are in the nucleus the more positively charged the nucleus is and the stronger the attraction of the electrons

distance from nucleus

the greater the distance of the outer electron from the nucleus the weaker the attraction

shielding

the greater the number of electrons between the outer electrons and the nucleus the weaker the attraction

ionisation is always an endothermic reaction

because you must put in energy to remove an electron from an atom or molecule

second ionisation energy

energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions to for 1 mole of gaseous 2+ ions

second ionisation > first ionisation

because electrons are being removed from a positive ion which requires more energy

successive ionisation energy

first ionisation energy decreases down group 2

evidence electron shells exist

• elements going down group 2 have 1 more electron shell between the nucleus and the outer electron

• this increases the distance between them which reduces the nuclear attraction

ionisation trend across period 3

ionisation trend across periods…

…generally increases because the proton number increases and the shielding effect stays the same

why does MAGNESIUM have a HIGHER ionisation energy than ALUMINIUM

• aluminium’s outer electron is on 3p rather than 3s so electrons are generally further from the nucleus

• 3p orbital has additional shielding provided by 3s

why does PHOSPHORUS have a HIGHER ionisation energy that SULFUR

• phosphorus and sulfur both have electrons in 3p however the first electron taken in phosphorus’ sub-shell is from a singly-occupied orbital

• the first electron taken in sulfur is from an orbital containing 2 electrons

• the repulsion between the 2 electrons makes it easier to remove from shared orbitals

1 electron from the 3rd shell and 11 electrons in total, ITS SODIUM

within each shell, successive ionisation energy increases…

…because electrons are being removed from increasingly positive ions, there’s less repulsion among the remaining electrons so they’re more strongly attracted to the nucleus