1. TOPIC 4: THE PERIODIC TABLE AND STRUCTURE OF ATOM
By:
Chemistry Lecturer
School of Allied Health Sciences
City University College of Science and Technology

2. HISTORY
There are about 115 elements on earth’s crust.
Many of this elements found in the form of compounds or mineral.
GROUP, PERIOD & PROTON NUMBERS:
Elements arranged in PT based on their proton numbers.
Have 18 vertical groups call GROUPS which named Group 1, 2, 13, 14….18.

3. Elements have similar chemical properties are placed in same group.
Have 7 horizontal rows called PERIODS which named Period 1, 2,3…7

4. Special names for some Groups:
Group 1,2,13 – group metals
Group – non metals (silicon & carbon)
GROUP
NAME 1
ALKALI METALS 2
ALKALINE EARTH METALS 17
HALOGENS 18
INERT NOBEL GASES
3-12
TRANSITION METALS

6. By knowing proton number of element- we can determine Group & Period it is placed in.
Element W has proton num 15. what Group & Period occupy in PT?
Num. proton = Num. electron = 15
Electron configuration = 2.8.5
= W has 3 electron shells & 5 valence electron
= valence electron 3 to 8 = +10
= = 15
= W placed in Period 3 and Group 15
*Period= look at number of shells
Group= look at valence number

7. Valence electrons = Group number Valence electron = 1, Group =1
Group 1 and 2
Valence electrons = Group number
Valence electron = 1, Group =1
Valence electron = 2, Group =2
Group 13-18
Group number = Valence electron + 10
Valence electron = 3, Group =13
Valence electron = 7, Group =17
Group
Period 1 2 13 14 15 16 17 18 H He Li
2.1 Be
2.2 B
2.3 C
2.4 N
2.5 O
2.6 F
2.7 Ne
2.8 3 Na
2.8.1 Mg
2.8.2 Al
2.8.3 Si
2.8.4 P
2.8.5 S
2.8.6 Cl
2.8.7 Ar
2.8.8 4 K Ca
Period number = number of filled electron shells
Na ; = Period 3
Li ; 2.1 = Period 2
K ; = Period 4

8. EXERCISE 1:
Elements P, Q, R, S, T have proton number 5, 9, 11, 14, 20. Write down electron configuration for each & give Group & Period:
ELEMENT
ELECTRON CONFIGURATION
GROUP
PERIOD P Q R S T

9. ANSWER 1:
Elements P, Q, R, S, T have proton number 5, 9, 11, 14, 20. Write down electron configuration for each & give Group & Period:
ELEMENT
ELECTRON CONFIGURATION
GROUP
PERIOD P
2.3 13 2 Q
2.7 17 R
2.8.1 1 3 S
2.8.4 14 T 12 4

10. As we go across a period from left to right PT:
The electronegativity increase
The atomic radius decrease
The oxides of elements show a decrease in basicity but increase in acidity
The atomic size decreases from sodium to argon because:
Increase number of electrons in same shells results in stronger electrostatic force exerted by protons on electron
Electrostatic force pulls the electron shells closer to nucleus  decrease in atomic size

11. GROUP 18 ELEMENTS (NOBLE GASES)
Helium (He)
Neon (Ne)
Argon (Ar)
Krypton (Kr)
Xenon (Xe)
Radon (Rn)
All noble gases can’t dissolve in water & can’t conduct electricity & heat.
Colourless gases with low meting & boiling point

12. Not chemically reactive because they exist as monoatomic gases – can’t combine ionically or covalently with other element.
It has attained duplet or octet electron arrangement
Have eight valence electron
As their valence shells complete, this atoms can’t accept, donate or share electrons with other elements.

13. USES OF GROUP 18 GROUP USES HELIUM Fill air ships & weather balloons
NEON
Burns with orange red colour – used to light up billboards on hotels, buildings & airport runways
ARGON
Used in filament bulbs to prevent burning of tungsten filament
KRYPTON
High speed flash bulbs in photography
Used in electric bulbs

14. GROUP 1 ELEMENTS ( Alkali metals)
Consist:
Lithium (Li)
Sodium (Na)
Potassium (K)
Rubidium (Rb)
Caesium (Cs)
Francium (Fr)
Soft & cut easily
Conduct heat & electricity
Hv high melting & boiling points

15. Chemical properties of alkalis metal
Reactive elements & must kept in paraffin
Cannot exist in free form – need combine with other elements.
Have 1 valence electron
During chemical reaction – they donate electron to obtain nose gas stability

16. GROUP 17 ELEMENTS (Halogens) Consists:
Fluorine (F)
Chlorine (Cl)
Bromine (Br)
Iodine (I)
Astatine (At)
Reactive non-metals
Found in minerals on earth’s crust
All halogen made up of diatomic molecules

17. Cannot conduct electricity
Weak conductors of heat because consist of covalent molecules
Chemical properties:
All halogen have 7 valence electrons.
During chemical reaction-halogen atoms receive electron to form anion-to attain the noble gas electron arrangement

18. The Transition Elements
Is metals which placed between Group 2 & G.13
Physical & chemical properties of elements are similar.
All period 4 transition metals are solids.
Atomic radius increase very slightly towards right.
Density, melting & boiling point increase across the period from Sc to Cu
Zn decrease in density, melting & boiling points.
Not reactive compared to alkalis metals because they have stronger metallic bonds among their atoms.

19. Have shining surfaces & high tensile strength.
Good conductors of heat & electricity
Special features:
Coloured ions – they form ions, compound & solutions which are coloured.
Complex ions
Varying oxidation numbers
Catalytic properties

20. Uses of Transition Elements in Industry
Used as catalyst in specific industrial process.
Mercury used in thermometers because its high melting & boiling point & liquid state
Tungsten – make filament because not melt easily
Iron- make vehicles & electrical appliances
Chromium – used to coat iron to prevent rusting of iron substance

21. SUMMARY Horizontal rows in periodic table of Element call periods.
The number given to each period indicates the number of filled electron shells.
Eg: period 3 shows all elements of that period have 3 shells filled with electron.
Number of proton increase across the period from left to right.
They increase by 1 proton.

22. Physical & chemical properties of the elements change gradually across the Period.
smaller the atom & closer the electron to nucleus  more difficult it release electrons to form cations or +ve ion – electropositivity decrease
Smaller the atom & more valence electron in last shell  easier to accept or share electrons with other atoms  electronegativity increase across period from sodium to argon.

23. THANK YOU!