Periodic table trends

Trends in the periodic table: Ionization Energy Atomic Radii Ionic Radii Electron Affinity Electronegativity Shielding

Background 04/10/99 Electrons can jump between shells (Bohr’s model supported by line spectra) The electrons can be pushed so far that they escape the attraction of the nucleus Losing an electron is called ionization An ion is an atom that has either a net positive or net negative charge Q: What would the charge be on an atom that lost an electron? Gained two electrons? A: +1 (because your losing a -ve electron) A: -2 (because you gain 2 -ve electrons)

IONIZATION ENERGY 04/10/99 Ionization energy is the energy required to remove one outer electron from an atom increase across, decrease down ( ,  ) increase across due to the increasing nuclear charge – takes more energy to remove electrons since they are closer to full valence shells decrease down due to electrons being further from the nucleus 1st ionization energy = energy required to remove 1st outermost electron 2nd ionization energy = energy required to remove 2nd outermost electron, etc. once electrons are removed from a neutral atom, atom is now an ion ion = atom or group of bonded atoms that has either a positive or negative charge

ATOMIC RADIUS and IONIC RADIUS Atomic radius is the distance from the nucleus to the outer electron shell decrease across, increase down (  ,  ) decrease across - atom has valence shell that is becoming full and electrons are being pulled closer to nucleus increase down - has a lot more electrons so is a larger atom Ionic radius is the distance from the nucleus to the outer electron shell decrease across, increase down (  ,  ) cations are always SMALLER than the neutral atoms from which they are formed due to the loss of the outer shell electrons resulting in increased attraction by the nucleus anions are always LARGER than the neutral atom because the nuclear attraction is less for increased number of electrons

Ionization energy vs. atomic number 04/10/99

Atomic radius vs. atomic number 04/10/99

IONIZATION ENERGY vs. ATOMIC RADIUS 04/10/99 IONIZATION ENERGY vs. ATOMIC RADIUS As one increases, the other decreases Ionization energy increases Atomic radius decreases And. . . Ionization energy decreases Atomic radius increases

Electron configuration of Na+ resembles Ne 04/10/99 11p+ 12n° 11p+ 12n° 10p+ 10n° Na has 11 electrons Na+ has 10 electrons Ne has 10 electrons Electron configuration of Na+ resembles Ne Alkali metals become like noble gases Radius increases because shells are added Increased radius will make it easier to lose an electron because of greater distance between positive and negative charges

Li (enc = 1) Be (enc = 2) B (enc = 3) + + + + + + + + + + + + Proton # increases. More protons means greater attraction between nucleus and outer electron thus higher ionization energy. The greater attraction also means that outer electrons are brought closer to the nucleus, thus smaller atomic radius results. 04/10/99 Li (enc = 1) Be (enc = 2) B (enc = 3) + + + + + + + + + + + +

04/10/99 ELECTRON AFFINITY Electron affinity is energy associated with an atom gaining an electron. increase across, decrease down (, ) decrease down due to a larger size of atom (they already have lots of electrons) energy that accompanies the addition of an electron to a gaseous atom F(g) + e-  F-(g) negative means the gain of an electron is favorable since energy is released positive means the gain of an electron is unfavorable since energy is absorbed it is highest in the top right where atoms are smallest with the greatest number of protons

ELECTRO-NEGATIVITY Electro-negativity is a number that describes the relative ability of an atom (when bonded) to attract electrons. the trend is the same as affinity for the same reason. increase across, decrease down ( ,  ) The tendency for an atom to attract electrons to itself when chemically combined Cs is the least and F is the most noble gases are omitted because they do not form compounds

SHIELDING this is how well the nucleus is surrounded by electrons remains constant across, increases down (constant  ,  ) *****NOTE: Ignore H when looking at trends, look at many periods/groups when summarizing trends Noble gases are ignored since they already have a full outer, valence, shell.