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SUBMITTED BY : SUMAN DAGAR
APPLIED SCIENCE
IONISATION ENERGY AND
ELECTRON AFFINITY
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If an electron is given enough energy (in the form of a
photon) to overcome the effective nuclear charge holding
the electron in the cloud, it can leave the atom completely.
Energy required to remove the outermost electron from an
atom
Amount of energy needed to remove ONE electron from a
neutral atom
Energy needed to remove electrons from ground state to
gaseous state in an atom
Formation of positive ions (cations)
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Formation of positive ions (cations)
The larger the atom is, the easier its electrons are to remove.
Ionization energy and atomic radius are inversely
proportional.
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Increases
Decreases
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Element Atomic # IE (kJ/mol)
Na 11 495.8
Mg 12 737.7
Al 13 577.6
S 16 999.6
Cl 17 1251.1
Ar 18 1520.5
K 19 418.8
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1st ionization energy
Energy required to remove 1st electron from atom
Taken from highest energy level
Easiest to remove
Energy increases as more electrons are removed
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Energy needed to remove additional electrons from an
atom
Energy increases as more electrons are removed.
Removing electrons from lower energy levels, close to
nucleus
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1st IE 2nd IE 3rd IE 4th IE
Na 495.8 4562.4 6912 9543
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Place these elements in order of INCREASING 1st ionization energy.
1) Mg, S, Si
2) As, N, P
(p. 321 in text)
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Creating negative ions (anions)
Energy change with the addition of an electron to an
atom
energy change that occurs when electrons added to gaseous
atom
Energy is released when electrons are added,
exothermic process (negative value)
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Electron tends to enter partially filled subshell or go to the next energy level
Does not follow predictable trend like atomic radii and ionization
energy
An atom’s “desire/affinity” for more electrons, wants to get more
electrons ! ! !
Metals—decrease electron affinity.
Nonmetals—increase electron affinity, more reactive
Stable atoms—full octet
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Increases
Decreases