tren across the periodic

2. Identify the position of an element in the periodic
table by its electron configuration
Periodic table is divided into several blocks

3. -To identify the block of an element, look for the
highest energy electron—orbital s,p,d,f???
-To identify period of an element, look for the
highest numbered main shell – 1,2,3,4….????
-To identify group of an element, look for the
total number of electrons in the outermost shell –
1,2,3,4,5..?

4. EXAMPLE
Electron
Block Period Group
configuration
1s2 2s2 2p6 3s2 3p6
3d10 4s2
1s2 2s2 2p6 3s2 3p6
3d54s2
1s2 2s2 2p6 3s2 3p6
4s2
1s2 2s2 2p6 3s2 3p4
1s2 2s2 2p6 3s2 3p6
3d14s2
1s2 2s2 2p3

5. -Atomic radius decreases across a periodic table
from left to right. WHY?
= Nuclear charge increases when across a
period from left to right, as the number of
proton in the nucleus increases.
= Although the number of electrons also increases, the
outer electrons are all in the same shell.
= Electrons are attracted more strongly to the nucleus.

6. Ionisation Energy = The minimum amount of energy
needed to remove one mole of electrons from one
mole of atoms in its gaseous state
X (g) X+ (g) + e ∆H=First ionisation energy
First ionisation energy increases arcoss a period
from left to right. WHY?
= As atomic radius decreases across a period.
= the strength of attraction between the outer
electrons and the nucleus increases.
=The energy required to remove the outermost
electron from an atom increases.

7. Electronegativity = The ability of an atom
to attract electrons toward itself.
When across a period from left to right,
electronegativity increases. WHY?
= Due to the stronger attraction that the
atoms obtain as the nuclear charge
increases

8. Metallic and non-metallic character
Example of metalloids = germanium, silicon, arsenic and
tellurium

9. When going down a Group…

10. Metal
-Down the Group
- Electronegativity decrease (No. of shell increase,
Distance between nucleus and outer shell electrons
increase)
- More able to donate electrons to form
cations

11. Non- metal
- Down the Group
- Electronegativity decrease, because the no
of shell and distance between nucleus and
outer electrons increase
- Non-metals become less able to accept
electrons to form anions

12. The element of group 18
-The Noble Gases
-Very unreactive gases
- have very low melting and boiling
temperature
-The lack of reactivity arises from the
arrangement of electrons in their
atoms – duplet & Octet