3.1 the periodic table
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state two similarities of elements in the same group
• similar chemical properties * similar outer shell configuration
periodicity is…
a repeating pattern across different periods
define first ionisation energy
the energy needed to remove one mole of electron from one mole of gaseous atom to form one mole of gaseous +1 ion
define second ionisation energy
the energy needed to remove one mole of electron from one mole of gaseous +1 ion to form one mole of gaseous +2 ion
give the equation for the first ionisation energy of mg
mg(g) —> mg+1(g) + e-
give the equation for the second ionisation energy of mg
mg+1(g) —> mg+2(g) + e-
name three factors that affect ionisation energy
• the attraction of the nucleus (nuclear charge) • distance from nucleus • shielding
helium has the largest first ionisation energy because….
there is no shielding but has more protons than H so more nuclear charge and stronger attraction to nucleus
why do ionisation energies decrease down a group
shielding increases down the group so there is less attraction to the nucleus so outer electrons are lost more easily
state and explain the general trend of ionisation energies across a period
increase of ionisation energy, protons increase therefore nuclear charge increases but shielding stays the same but size of atom decreases so attraction of outer electrons to nucleus increases
explain the dip in ionisation energies across a period from group 2 to 3
nuclear charge increases as protons increase, outer electrons in group 2 are in s orbital but in group 3 they are in p orbital which is higher in energy so ionisation energy decreases
explain the dip in ionisation energies across a period from group 5 to 6
in group 6 the electrons have begun pairing up which causes inorbital repulsion which decreases ionisation energy
state and explain in atomic radii across a period
decrease in atomic radii, shielding stays the same, protons increase therefore nuclear charge increases so there is more attraction between electrons and nucleus so shells are pulled inward
state and explain the trend of electronegativity across a period
number of protons increase so nuclear charge increases, size of atom decreases so there is stronger attraction from nucleus to the two electrons in a covalent bond
explain the trend in melting and boiling points across a period
metals- high, strong metallic bonds, size of ion decreases across the period so sea of free electrons increases giant covalent- v high, strong covalent bonds lots of energy needed to break simple molecular- low, weak london forces between molecules, the more e- the stronger forces monatomic- v low, weak london forces between atoms