The Periodic Table and Ionic Bonding:

Part 4-Periodic Table Trends

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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

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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 #3Ionization Energy (I.E.)

• Ionization energy- energy needed to remove an electron from an atom and form a positive ion

• Generic formula: X(atom) + ionization energyX+1(ion) +

electron• Specific example: Na + 119 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):

119 176 138 188 242 239 299 363

Periodic Trend #3Ionization Energy (I.E.)

• DOWN GROUPS ionization energy generally DECREASES as electrons in higher energy levels farther away from the positive nucleus

ATOM I.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 #3Ionization Energy (I.E.)

Periodic Trend #3Ionization 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 #3Ionization Energy (I.E.)

A metal will lose enough electrons to have a stable electron structure noble gas or core atom (s2p6)

• Metals in Group I with electron configurations ending in s1 will lose 1 electron and form +1 ions

• Metals in Group II with electron configurations ending in s2 will lose 2 electrons and form +2 ions

• Metals in Group III with electron configurations ending in s2p1 will lose 3 electrons and form +3 ions

Periodic Trend #3Ionization Energy (I.E.)

Electron Configuration Comparison

Atom config. of atom Ion config of ionNa 1s22s22p63s1 Na+1

1s22s22p6

Mg 1s22s22p63s2 Mg+2 1s22s22p6

Al 1s22s22p63s23p1 Al+3 1s22s22p6

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

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