Reactivity
– When reacting, atoms collide so their outer-most
electrons (valence electrons) interact
• Those electrons that are “seen” by another atom or
molecule
– Valence electrons are the reacting electrons
– Some atoms gain electrons, while others lose them
• metals are “born losers”
– always give up their electrons to become more stable (to end with
a complete valence shell – a complete octet)
• non-metals acquire those electrons lost by the metal
– take on electrons to become more stable (to fill up their orbitals
and complete the octet)
1
Silver (Ag)
– In the 1s22s22p63s23p64s23d104p65s14d10 state
• 1 valence electron to react
– Ag wants to lose the electron, emptying its 5s-sublevel
– Becomes Ag+
» 47 protons but only 46 electrons
– The +1 ion is the most stable configuration that
Ag can be in
2
Lead (Pb)
– Pb has a partially filled and a completely filled
sublevel as its valence shell
• 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2
• 1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p2
Valence Electrons
– Pb wants to exist in the lowest energy state
possible
• Pb loses 6p2 electrons to become Pb2+ ion - lead(II)
– 1s22s22p63s23p63d104s24p64d104f145s25p65d106s2
• Pb loses 6s26p2 electrons to become Pb4+ ion – lead(IV)
–1s22s22p63s23p63d104s24p64d104f145s25p65d10
3
Tin (Sn)
– Tin has very similar properties to lead, except that
its most abundant state is Sn4+ - tin(IV)
• 1s22s22p63s23p64s23d104p65s24d105p2
• 1s22s22p63s23p63d104s24p64d105s25p2
Valence Electrons
• Lose 5s25p2 electrons to become Sn4+
• Lose just 5p2 electrons to become Sn2+
4
Bismuth (Bi) and Thallium (Tl)
– Both bismuth and thallium exhibit similar reactivity
• Tl: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p1
– 1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p1
• Tl can lose either the 6p1 or the 6s26p1 electrons to
form a +1 or +3 species respectively
• Bi: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p3
– 1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p3
• Bi can lose the 6p3 or the 6s26p3 electrons to form the
+3 or +5 ions respectively
5
Halogens
– The halogens have a similar desire for stability
and lower energy, but it’s acquired differently
• Fluorine
– 1s22s22p5
[He] 2s22p5
• Chlorine
– 1s22s22p63s23p5 [Ne] 3s23p5
• Bromine
What do you notice
about the valence
electrons?
– 1s22s22p63s23p64s23d104p5
– 1s22s22p63s23p63d104s24p5
– All halogens have a completely filled s-sublevel
and are 1 electron from a full p-sublevel
• They can gain 1 electron to fill their p-sublevels
– “Completing the octet”
6
Halogens
– When the halogens gain an electron, they
become -1 anions (F-, Cl-, Br-)
– In completing their octets, halogens become
isoelectronic with the next element, the noble gas
• Two species are isoelectronic if they have the same
electronic configurations
– F- is isoelectronic with Ne
» 1s22s22p6
– Cl- is isoelectronic with Ar
» 1s22s22p63s23p6
– Br- is isoelectronic with Kr
» 1s22s22p63s23p64s23d104p6
7
To be isoelectronic …
– O2- is isoelectronic with Ne
•1s22s22p6
– The same way that non-metals can be
isoelectronic with the noble gases, metals can too
• Na+ (losing the 3s1 electron) is isoelectronic with Ne
– 1s22s22p6
(complete octet is in the 2nd energy level)
• Sr2+ is isoelectronic with Kr
– 1s22s22p63s23p64s23d104p6
• Fr+ is isoelectronic with Rn
– 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
8
Metals and Isoelectronic
– Some metals have similar (but not exact) electron
configurations to other atoms when charged
– Zn can lose its 4s2 electrons, giving it the same
valence configuration as Ar
• 1s22s22p63s23p63d104s2
• Zn has a full d-sublevel, whereas Ar does not
– Zn2+:
– Ar:
1s22s22p63s23p63d10
1s22s22p63s23p6
• Zn is pseudo-isoelectronic with Ar
9
Isoelectronic or Pseudoisoelectronic?
– State whether the atoms are isoelectronic or
pseudoisoelectronic with the indicated noble gases
• Na+
• Ca2+
• Cu+
• I• Pd4+
• Hf4+
Ne
Ar
Ar
Xe
Kr
Xe
Isoelectronic
Isoelectronic
Pseudo-isoelectronic
Isoelectronic
Pseudo-isoelectronic
Isoelectronic
10
Electronic Trends in the Periodic Table
Alkali Metals (Group 1)
–H
– Li
– Na
–K
– Rb
– Cs
– Fr
1s1
1s22s1
1s22s22p63s1
1s22s22p63s23p64s1
1s22s22p63s23p64s23d104p65s1
1s22s22p63s23p64s23d104p65s24d105p66s1
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s1
11
Electronic Trends in the Periodic Table
Alkaline Earth Metals (Group 2)
– Be
– Mg
– Ca
– Sr
– Ba
– Ra
1s22s2
1s22s22p63s2
1s22s22p63s23p64s2
1s22s22p63s23p64s23d104p65s2
1s22s22p63s23p64s23d104p65s24d105p66s2
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s2
12
Electronic Trends in the Periodic Table
Halogens (Group 17)
–F
– Cl
– Br
–I
– At
1s22s22p5
1s22s22p63s23p5
1s22s22p63s23p64s23d104p5
1s22s22p63s23p64s23d104p65s24d105p5
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p5
13
Electronic Trends in the Periodic Table
Nobel Gases (Group 18)
– He
– Ne
– Ar
– Kr
– Xe
– Rn
1s2
1s22s22p6
1s22s22p63s23p6
1s22s22p63s23p64s23d104p6
1s22s22p63s23p64s23d104p65s24d105p6
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
14