1. Lecture 5

2. Electronic Configuration of Periodic Table
shells 1s K 2 s p L 3 M 4 3d d N 5 4d O 6 5d P 7 6d
p block
d block f
f block
s block

3. Electronic Configuration of Periodic Table
Aufbau Principle: Add one proton to nucleus and one electron to the lowest-energy orbital available in the electron shell.
s block: 2 boxes  1 orbital  2 electrons. For s: l= 0; m= 0 i.e. 1 orbital on s subshell.
p block: 6 boxes  3 orbitals  with 2 electrons each.
For p: l=1; m= -1, m= 0, m= 1 i.e. 3 orbitals on p subshell
d block: 10 boxes  5 orbitals  with 2 electrons each.
For d: l = 2; m = -2, m = -1, m= 0, m =1, m =2 i.e. 5 orbitals on d subshell
f block: 14 boxes  7 orbitals  with 2 electrons each.
For f: l =3; m =-3, m =-2, m =-1, m =0, m =1, m =2, m =3 i.e. 7 orbitals on f subshell

4. Electron Energy Diagrams
A visual method of showing the energy of electrons within an element: 3 steps to build an energy diagram:
e.g. Iron [Fe] Z=26  26 protons  26 electrons
Step 1: Write down shorthand electronic configuration.
Step 2: Build energy diagram with subshells
Step 3: Fill in electrons with arrows counting up to Z.
Step s2 2s2 2p6 3s2 3p6 4s2 3d6 (short hand)

5. Electron Energy Diagrams
A visual method of showing the energy of electrons within an element: 3 steps to build an energy diagram:
e.g. Iron [Fe] Z=26  26 protons  26 electrons
Step 1: Write down shorthand electronic configuration.
Step 2: Build energy diagram with subshells
Step 3: Fill in electrons with arrows counting up to Z.
Step s2 2s2 2p6 3s2 3p6 4s2 3d6 (short hand)

6. Electron Energy Diagrams3p 3s 2p 2s 1s
Step 2
Step 3

7. Valence Electrons
Every element has both core electrons and valence electrons, e.g. Magnesium: Mg Z=12  12 electrons:
1s2 2s2 2p6 3s2
core electrons valence electrons
Core electrons are electrons in fully filled shells
Valence electrons are electrons in the outermost shell that is not fully filled with the exception of the noble gases that all have fully filled shells
He: 1s2, Ne: {He} 2s2 2p6,
Ar: {Ne} 3s2 3p6, Kr: {Ar} 4s2 3d10 4p6,
Xe: {Kr} 5s2 4d10 5p6. Rn: {Xe} 6s2 4f14 5d10 6p6 .

8. Construction of the Periodic Table
Electron shells fill in a systematic fashion so that patterns can be recognised in the electronic configuration.
Elements listed in horizontal Rows are called Periods. A new period is started each time the value of the principle quantum number, n, increases, i.e. each time the valence electrons enter a new shell.
Arrange rows so that elements with similar electronic configuration lie above one another to form vertical columns called Groups, similar electronic configuration meaning similar chemistry.

9. Group Properties
Group 1 - elements with only one valence electron: These are called the Alkali-Metal Group
Electronic configuration
3Lithium Li {He}2s1
11Sodium Na {Ne}3s1
19Potassium K {Ar}4s1
37Rubidium Rb {Kr}5s1
55Cesium Cs {Xe}6s1
87Francium Fr {Rn}7s1
Physical Properties
metals i.e good conductors, soft,
low melting point and boiling point

10. Group I Chemical Properties;
Na. + :Cl . → NaCl (Na+ and :Cl :- )
Alkali + Halogen → Ionic Compound
Na. + H2O → NaOH + H+
Alkali + Water → Ionic Compound
NaOH → Na+ + OH-
cations: positive ions (e.g. Na+, K+, H+)
anions: negative ions (Cl, OH)
Me → Me+ + e (Me = Alkali metal)

11. Group 17 (or 7A) Halogens
Elements with one electron less than their nearest nobel gas: The Halogens: (Greek: halogen=salt former)
Electronic Configuration:
9Fluorine F {He}2s22p5
17Chlorine Cl {Ne}3s23p5
35Bromine Br {Ar}4s23d104p5
53Iodine I {Kr}5s24d105p5
Physical Properties:
Highly coloured - volatile - non-metals - bad conductors - occur in nature as diatomic molecules X2 (X=Halogen), e.g. Cl2. F2 and Cl2 are gases, Br2 is a liquid and I2 is a solid.

12. Chemical Properties of the Halogens
X H  HX
or better:
X H2  2 HX
X Me  MeX (Me+ + X) (see group 1)
Aqueous solutions of HX contain high concentrations of H+, i.e. are acids:
HX + H2O  H+ + X- + H2O

13. Group 18 (or 8A) - The Noble Gases
Special group of elements within the periodic table. They all have full electron shells and are highly non-reactive.
Physical properties: Colourless gases (at normal temperature and pressure) – lowest boiling and melting points of all elements.
Chemical properties: The most chemically unreactive of all elements, up to recently thought to be totally unreactive and were called Inert Gas Elements.
Summary
Groups (columns) have similar electronic configuration and similar chemistry, e.g., Noble gases have full shells, Alkali metals have one electron more than Noble gases. Halogens have one electron less than Noble gas configuration.

14. Summary Continued.
Properties of Periods (Rows): Periods are characterised by the gradual filling of valence shells – all atoms in a period have different electronic configuration.
Similar chemical behaviour is not expected, however a gradual change of the metallic properties of Group 1 to the non-metallic properties of Group 17 is expected.