Monday 28th May , 2024
ONLINE CLASS
IX
CHEMISTRY
By: Rubia saif
Objective : Students will be able to illustrate
atomic size and its trend in periodic table.
Chapter 04
PERIODIC TABLE AND PERIODICITY OF
PROPERTIES
RECAP::
• Periodic table
• 7 periods and 18 groups
• Four blocks s, p, d ,f
• Group no. = charge on an ion
IA =Alkali metals +1
IIA =alkaline earth metals +2
IIIA =Boron family +3(exception)
IVA =Carbon family Sharing
VA =Nitrogen Family -3
VIA= Chalcogens -2
VII A = Halogens -1
VIII A = Noble gases queens
• Finding out position from E.C
• ( valence shell tells us Periods no. )
• (Valence electron tells us group no)
• Finding out valence shell E.C from postion
In this chapter we will learn::
1.ATOMIC SIZE
2.SHEILDING EFFECT
3.IONIZATION ENERGY
4.ELECTRON AFFINITY
5.ELECTRONEAGTIVITY
• DEFINITION
• TREND IN PERIODIC TABLE .
DOWN THE GROUP
ACROSS THE PERIOD
ATOMIC SIZE / ATOMIC RADIUS
DEFINITION:
• The distance in atom from centre of its nucleus to its outermost
shell is called atomic radius.
• Atomic size can be measured by atomic radius..
• Greater atomic radius the size will be greater and vice versa.
TREND IN PERODIC TABLE
• DOWN THE GROUP
Atomic size increases as we move from top to bottom in a group.
Reasons:
1.Due to increase in electronic shells.
Atomic radius increases so size of an atom will be increased.
• ALONG THE PERIOD:
Atomic size decreases along the period as we move from left to right in a
period.
Reasons:
1.Due to increased attractive forces between valence electrons and nucleus
.
2.Electrons are added up in same shell.
Shell no. Remains constant but prgressively increase in nuclear charge
causes atom to shrink.
Recapitulation:
Answer the following:
• Based on their positions in the periodic table, predict which has
the smallest atomic radius: Mg, Sr, Si, Cl, I
•
Based on their positions in the periodic table, predict which has
the largest atomic radius: Li, Rb, N, F, I
• K has greater atomic radius than Na. Justify !
• NOTEBOOK WORK:
SOLVE ASSESSMENT RELATED TO TOPIC GIVEN IN YOUR TEXT
BOOK.
