The Periodic Table and Ionic Bonding: Part 4-Periodic Table Trends 1

Objectives -Explain what an ion is and how it forms with energy -Describe what ionization energy is and how ionization energy trends are shown in the periodic table 2

Ions Ion- charged atoms protons ≠ electrons Ex.) –Na atom 11 protons, 11 electrons = neutral –Na ion 11 protons, 10 electrons = +1 charge New electron structures so ions have different properties than the atoms from which they were formed

Periodic Trend #3 Ionization Energy (I.E.) Ionization energy- energy needed to remove an electron from an atom and form a positive ion Generic formula: X(atom) + ionization energy  X +1 (ion) + electron Specific example: Na Kcal/mole  Na +1 + electron Positive ion with 1 less electron than protons –Positive ions = “cations” –Smaller radius than original atoms

ACROSS PERIODS ionization energy generally INCREASES –Increased attraction between the + nucleus and the electrons ATOM: Na Mg Al Si P S Cl Ar I.E. (kcal/mole): Periodic Trend #3 Ionization Energy (I.E.)

DOWN GROUPS ionization energy generally DECREASES as electrons in higher energy levels farther away from the positive nucleus ATOMI.E. (kcal/mole) H 314 Li 124 Na 119 K 100 Rb 96 Cs 90 Cesium’s outer electron is much further away from the nucleus, therefore it is easier to remove Periodic Trend #3 Ionization Energy (I.E.)

Lower ionization energy = more chemically reactive element Metals have low ionization energies Few electrons in highest energy level and they are weakly held and easily removed Periodic Trend #3 Ionization Energy (I.E.)

A metal will lose enough electrons to have a stable electron structure noble gas or core atom (s 2 p 6 ) Metals in Group I with electron configurations ending in s 1 will lose 1 electron and form +1 ions Metals in Group II with electron configurations ending in s 2 will lose 2 electrons and form +2 ions Metals in Group III with electron configurations ending in s 2 p 1 will lose 3 electrons and form +3 ions Periodic Trend #3 Ionization Energy (I.E.)

Electron Configuration Comparison Atom config. of atom Ion config of ion Na 1s 2 2s 2 2p 6 3s 1 Na +1 1s 2 2s 2 2p 6 Mg 1s 2 2s 2 2p 6 3s 2 Mg +2 1s 2 2s 2 2p 6 Al 1s 2 2s 2 2p 6 3s 2 3p 1 Al +3 1s 2 2s 2 2p 6 not stable stable [Ne]

I.E. (cont.) Transition and rare earth elements –Lose electrons from several sublevels so charge will vary Nonmetals do NOT form positive ions –They have almost full outer energy levels and would have to lose too many electrons to form a positive ion like a noble gas

Objectives -Explain what an ion is and how it forms with energy -Describe what ionization energy is and how ionization energy trends are shown in the periodic table 12