Periodic Trends PDF

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In this note paper it talks about ionization energy, electron affinity, atomic radii, and effective nuclear charge. There are pictures for each periodic trend showing how each increases and decreases in the periodic table....

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Periodic Trends Effective Nuclear Charge (Zeff): Nuclear Attraction to the Electrons  Effective nuclear charge describes the pull/attraction force of the nucleus (protons) that an atom’s electron experiences.  Factors influencing Zeff:  The closer the electrons are to the nucleus the greater the attraction.  The orbitals that the electron resides.  Screening Effect  The greater the Zeff then the more tightly the atom’s electrons are held & therefore the more energy will be needed to remove the electrons. General Trend: • Zeff increases going across period • Zeff decreases going down period

Effective Nuclear Charge: Screening Effect  The general trend for Zeff is that it increases across a period.  Reason: ineffective shielding by the inner electrons in atomic orbitals (subshells).  The shielding ability of subshells: s>p>d>f  Zeff can be approximated:  [Z (atomic #) - (# inner electrons)] = Zeff  Example:  Pull felt by 2s electron in Li  Zeff = 3 - 2 = 1

Atomic Radii  Size increase going down a group as a consequence of a decrease in Zeff and being a farther distance from the nucleus. • As electrons are added in different levels (shell) further from the nucleus, there is less attraction by the protons in the nucleus to the orbiting electrons.  Size increase going down a group as a consequence of a decrease in Zeff and being a farther distance from the nucleus. • Ineffective shielding of the orbitals (subshells), resulting in an increase in attraction by protons in the nucleus to the orbiting electrons

Ionization Energy (IE) Ionization energy is the energy required to remove an electron from an atom in the gas phase. Generic Representation: Energy + A (g)  electron + A+ (g) Trend:

 IE increases across a period because Zeff increases due to poor shielding ability of the p & d orbitals electrons.  IE decreases going down a column due to increase in distance from the nucleus and decrease in Zeff.  This is why metals lose electrons more easily than nonmetals & are good reducing agents; they have lower IE.  This is why nonmetals lose electrons with difficulty; they have higher IE.

Electron Affinity (EA)  Electron affinity is the change (E) in energy required when an atom gains an electron to form an anion.  Generic Representation: A(g) + e-  A- (g) EA = ∆E  General Trend:  EA increases across a period  (EA becomes more positive) due to increase in Zeff.  EA decreases down a group  (EA becomes less positive) due to decrease in Zeff.  Electron affinity greatest for halogens  EA greater for nonmetals (anions) vs. metals (cations).  A LARGER EA value means very STABLE ion....