ATOMIC ELECTRON CONFIGURATIONS AND PERIODICITY
1
2
3
Arrangement of Electrons in Atoms
Arrangement of Electrons in Atoms
Electrons in atoms are arranged as
Each orbital can be assigned no more than 2 electrons!
SHELLS (n)
This is tied to the existence of a 4th
electron spin quantum number, ms.
SUBSHELLS (l)
quantum number, the
ORBITALS (ml)
4
Electron Spin Quantum Number, ms Can Can be be proved proved experimentally experimentally that that electron electron has has aa spin. spin. Two Two spin spin directions directions are are given given by by m mss where where m mss == +1/2 +1/2 and and -1/2. -1/2.
5
6
Electron Spin Quantum Number QUANTUM QUANTUM NUMBERS NUMBERS nn ---> ---> shell shell
1, 1, 2, 2, 3, 3, 4, 4, ... ...
ll ---> ---> subshell subshell
0, 0, 1, 1, 2, 2, ... ... nn -- 11
field field
m mll ---> ---> orbital orbital
-l-l ... ... 00 ... ... +l +l
Paramagnetic Paramagnetic:: substance substance is is attracted attracted to to aa
m mss ---> ---> electron electron spin spin
+1/2 +1/2 and and -1/2 -1/2
Diamagnetic Diamagnetic:: NOT NOT attracted attracted to to aa magnetic magnetic magnetic magnetic field. field. Substance Substance has has unpaired unpaired electrons. electrons electrons..
Page 1
7
8
Electrons Electrons in in Atoms Atoms
Pauli Exclusion Principle
this shell has a single orbital (1s) to which 2e- can be assigned. When n = 2, then l = 0, 1
That is, each electron has a unique address.
2s orbital
2e-
three 2p orbitals
6e-
TOTAL =
8e-
10
Electrons Electrons in in Atoms Atoms When n = 4, then l = 0, 1, 2, 3 4s orbital 2ethree 4p orbitals 6efive 4d orbitals 10eseven 4f orbitals 14eTOTAL = 32e-
And Andmany manymore! more!
When When nn == 3, 3, then then ll == 0, 0, 1, 1, 22 3s 2e3s orbital orbital 2ethree 6ethree 3p 3p orbitals orbitals 6efive 10efive 3d 3d orbitals orbitals 10eTOTAL 18eTOTAL == 18e-
When n = 1, then l = 0
No two electrons in the same atom can have the same set of 4 quantum numbers.
9
Electrons Electrons in in Atoms Atoms
11
Assigning Assigning Electrons Electrons to to Atoms Atoms •• Electrons Electrons generally generallyassigned assignedto to orbitals orbitals of of successively successively higher higher energy. energy. •• For For H H atoms, atoms, EE == -- C(1/n C(1/n22).). EE depends depends only only on n. on n. •• For For many-electron many-electron atoms, atoms, energy energy depends depends on on both both nn and and l.l. •• See See Figure Figure 8.6, 8.6, page page 342 342 and and Screen Screen 8. 8. 5. 5.
Page 2
12
Assigning Electrons to Subshells • In H atom all subshells of same n have same energy. • In many-electron atom: a) subshells increase in energy as value of n + l increases. b) for subshells of same n + l, subshell with lower n is lower in energy.
13
14
Effective Nuclear Charge Electron Filling Order
• Z* is the nuclear charge experienced by the outermost electrons. See p. 344 and
The reason for difference in energy for 2s and 2p subshells, subshells, for example, is effective nuclear charge, Z*.
Screen 8.6. • Explains why E(2s) < E(2p) • Z* increases across a period owing to incomplete shielding by inner electrons. • Estimate Z* by --> [ Z - (no. inner electrons) ] • Charge felt by 2s e- in Li Z* = 3 - 2 = 1 • Be Z* = 4 - 2 = 2 • B Z* = 5 - 2 = 3 and so on!
Figure 8.7
16
Writing Writing Atomic Atomic Electron Electron Configurations Configurations Two Two ways ways of of writing configs writing configs. configs.. One One is is called called the the
spectroscopic spectroscopic notation. notation.
SPECTROSCOPIC NOTATION for H, atomic number = 1
1
1s
value of n
no. of electrons value of l
Writing Writing Atomic Atomic Electron Electron Configurations Configurations Two Two ways ways of of writing writing configs. . Other configs configs. Other is is called called the the orbital orbital box box notation. notation.
15
Effective Effective Nuclear Nuclear Charge, Charge, Z* Z*
17
18
ORBITAL BOX NOTATION for He, atomic number = 2 Arrows 2 depict electron spin 1s
1s
One electron has n = 1, l = 0, m l = 0, ms = + 1/2 Other electron has n = 1, l = 0, m l = 0, ms = - 1/2
Page 3
See “Toolbox” for Electron Configuration tool.
19
20
Lithium Lithium
21
Boron Boron
Beryllium Beryllium
Group 1A Atomic number = 3 1s22s1 ---> 3 total electrons 3p
Group 2A Atomic number = 4 1s22s2 ---> 4 total electrons
3p
3p
3s
2p
2s
2s
1s
1s
3s
3s 2p
2p
2s 1s
22
23
Carbon Carbon
3p
2p 2s 1s
Here we see for the first time HUND’S RULE . When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible.
24
Nitrogen Nitrogen
Group 4A Atomic number = 6 1s2 2s2 2p2 ---> 6 total electrons 3s
Group 3A Atomic number = 5 1s2 2s2 2p1 ---> 5 total electrons
3p
Oxygen Oxygen Group 6A Atomic number = 8 1s2 2s2 2p4 ---> 8 total electrons
Group 5A Atomic number = 7 1s2 2s2 2p3 ---> 7 total electrons
3s
3p 3s
2p
2p
2s
2s
1s
1s
Page 4
25
26
Neon Neon
Fluorine Fluorine
Electron Configurations of p-Block Elements
Group 8A Atomic number = 10 1s2 2s2 2p6 ---> 10 total electrons
Group 7A Atomic number = 9 1s2 2s2 2p5 ---> 9 total electrons
3p
3p
3s
3s
2p
2p
2s
2s
27
Note that we have reached the end of the 2nd period, and the 2nd shell is full!
1s
1s
28
Sodium Sodium Group 1A Atomic number = 11 1s2 2s2 2p6 3s1 or “neon core” + 3s 1 [Ne] Ne] 3s1 (uses rare gas notation) Note that we have begun a new period.
All Group 1A elements have [core]ns 1 configurations.
29
Group 5A Atomic number = 15 1s2 2s2 2p6 3s2 3p3 [Ne] Ne] 3s2 3p3
Group 3A Atomic number = 13 1s2 2s2 2p6 3s2 3p1 [Ne] Ne] 3s2 3p1 3p
All Group 3A elements have [core] ns2 np1 configurations where n is the period number.
Page 5
30
Phosphorus Phosphorus
Aluminum Aluminum
3s 2p 2s 1s
All Group 5A elements have [core ] ns 2 np3 configurations where n is the period number.
3p 3s 2p 2s 1s
31
32
Calcium Calcium Group 2A Atomic number = 20 1s2 2s2 2p6 3s2 3p6 4s2 [Ar] Ar] 4s2 All Group 2A elements have [core]ns2 configurations where n is the period number.
Transition Element Configurations
• • • •
All 4th period elements have the configuration [argon] nsx (n - 1)d 1)dy and so are “d-block” elements.
Gray = s block Orange = p block Green = d block Violet = f block
34
Chromium Iron
35
Lanthanides Lanthanides and and Actinides Actinides
33
Transition Transition Metals Metals Table Table 8.4 8.4
Relationship of Electron Configuration and Region of the Periodic Table
Copper
Lanthanide Element Configurations
All these elements have the configuration [core] nsx (n - 1)d 1)dy (n - 2)f 2)fz and so are “f-block” elements. 3d 3d orbitals orbitals used used for for Sc Sc -- Zn Zn (Table (Table 8.4) 8.4)
Cerium [Xe] Xe] 6s2 5d1 4f1 Uranium [Rn] Rn] 7s 2 6d1 5f3
Page 6
4f 4f orbitals orbitals used used for for Ce Ce -- Lu Lu and and 5f 5f for for Th Th -- Lr Lr (Table (Table 8.2) 8.2)
36
Ion Ion Configurations Configurations
37
To form cations from elements remove 1 or more e- from subshell of highest n [or highest (n + l)]. P [Ne [Ne]] 3s2 3p3 - 3e- ---> P3+ [Ne [Ne]] 3s2 3p0
Ion Ion Configurations Configurations
38
39
Ion Ion Configurations Configurations
To form cations from elements remove 1 or more e- from subshell of highest n [or highest (n + l)]. P [Ne [Ne]] 3s2 3p3 - 3e- ---> P3+ [Ne [Ne]] 3s2 3p0
For transition metals, remove ns electrons and then (n - 1) electrons.
Fe [Ar [Ar]] 4s2 3d6 loses 2 electrons ---> Fe 2+ [Ar [Ar]] 4s0 3d6
3p
3p 3s
3s
2p
2p 2s
2s
1s
1s
40
41
42
Ion Ion Configurations Configurations
Ion Ion Configurations Configurations
For transition metals, remove ns electrons and then (n - 1) electrons.
For transition metals, remove ns electrons and then (n - 1) electrons.
How do we know the configurations of ions? Determine the magnetic properties of ions.
Fe [Ar [Ar]] 4s2 3d6 loses 2 electrons ---> Fe 2+ [Ar [Ar]] 4s0 3d6
Fe [Ar [Ar]] 4s2 3d6 loses 2 electrons ---> Fe 2+ [Ar [Ar]] 4s0 3d6
Ions with UNPAIRED ELECTRONS are PARAMAGNETIC .
Fe2+
Fe 4s
3d
4s
3d
Fe2+
Fe 4s
3d
4s
3d
Fe3+ 4s
Page 7
3d
Ion Ion Configurations Configurations
Without unpaired electrons DIAMAGNETIC .
