the periodic table and ionic bonding: part 4-periodic table trends 1
TRANSCRIPT
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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