IB Chemistry on Periodic Trends, Effective Nuclear Charge and Physical properties.

1. Periodic Table of elements – divided to Groups, Periods and Blocks
Period- Horizontal row
• 7 periods/row
• Same number of shell
Groups – Vertical column
• Same number of valence electron
• Same number outmost electrons
Group 1
Block – different region in periodic table
• s, p, d, f blocks
• s block- elements with valence e in s sublevel
• p block – elements with valence e in p sublevel
18
Periods
1
7
Excellent site from periodic videos
Click here to view
s block
- s orbitals partially fill
d block
• d orbitals partially fill
p block
• p orbital partially fill
f block
• f orbital partially fill

2. s block elements
• s orbitals partially fill
1
H
He
p block elements
• p orbital partially fill
5
1s2
n = 2 period 2
B
[He] 2s2 2p1
6
1s1
2
Periodic Table – s, p d, f blocks elements
C
[He] 2s2 2p2
7
N
[He] 2s2 2p3
3
Li
[He] 2s1
8
O
[He] 2s2 2p4
4
Be
[He] 2s2
9
F
[He] 2s2 2p5
11
Na
[Ne] 3s1
10
Ne
[He] 2s2 2p6
12
Mg
[Ne] 3s2
13
Al
[Ne] 3s2 3p1
14
20
K
Ca
[Ne] 3s2 3p2
[Ar]
15
P
[Ne] 3s2 3p3
[Ar]
4s2
16
S
[Ne] 3s2 3p4
17
19
Si
4s1
CI
[Ne] 3s2 3p5
18
Ar
[Ne] 3s2 3p6
d block elements
• d orbitals partially fill
• transition elements
21
Sc
[Ar] 4s2 3d1
22
Ti
[Ar] 4s2 3d2
23
V
[Ar] 4s2 3d13
24
Cr
[Ar] 4s1 3d5
25
Mn
[Ar] 4s2 3d5
26
Fe
[Ar] 4s2 3d6
27
Co
[Ar] 4s2 3d7
28
Ni
[Ar] 4s2 3d8
29
Cu
[Ar] 4s1 3d10
30
Zn
[Ar] 4s2 3d10
f block elements
• f orbitals partially fill
Video on electron configuration
Click here electron structure
Click here video on s,p,d,f notation
Click here video s,p,d,f blocks,

3. Periodicity
Predicted pattern/trends in physical/chemical properties across period.
Physical properties
Chemical properties
Physical change - without change in molecular composition.
– appearance change
- composition remain unchanged.
Element properties
•
•
•
•
•
Atomic properties
•
•
•
•
Color, texture, odor
Density, hardness, ductility
Brittleness, Malleability
Melting /boiling point
Solubility, polarity
•
•
Ionization
energy
Periodic Trends
Across period 2/3
Down group 1/17
Atomic/ionic
radii
Gp 1
period 2
period 3
Ionization energy
Atomic radii
Ionic radii
Electronegativity
Melting
point
Electronegativity
Gp 17
Chemical change – diff composition from original substances
- chemical bonds broken/ formed
- new products formed

4. Why IE increases across the period?
Why IE decreases down a group ?
Ionization energy (IE)
1st Ionization energy
Min energy to remove 1 mole e from
1 mole of element in gaseous state
M(g)  M+ (g) + e
2nd Ionization energy
Min energy to remove 1 mole e from
1 mole of +1 ion to form +2 ion
M+(g)  M2+ (g) + e
Ionization energy
Factors affecting ionization energy
1
2
Distance from nucleus
3
Nuclear charge
electron
+3
+4
+5
+6
Effective Nuclear Charge (ENC)/(Zeff)
• Screening effect/shielding
• Effective nuclear charge (ENC)/(Zeff)
(Zeff) = Nuclear charge (Z) – shielding effect
• Net positive charge felt by valence electrons.
Nuclear charge increase
Distance near to nucleus – IE High 
Distance far away nucleus – IE Low 
Nuclear charge high (more proton) – IE High 
Nuclear charge low  (less proton) – IE Low 
+6
Inner electron – shield valence e from positive nuclear charge
Distance near
Nuclear charge 
Higher electron/electron repulsion
Strong electrostatic forces
attraction bet nucleus and e
Strong electrostatic forces
attraction bet nucleus and e
Easier valence e to leave
IE – High 
IE – High 
IE – Low 

5. IE drop from Be to B and N to O
Ionization Energy- Period 2
Why IE increases across the period 2?
IE increases across period 2
Nuclear charge increase 
Strong electrostatic forces
attraction bet nucleus and e
IE – High 
Li
Be
B
C
N
O
F
Ne
2p
2s
1s
1s2 2s1
1s2 2s2
1s2 2s2 2p1
1s2 2s2 2p2
IE drop  from Be to B
1s2 2s2 2p3
1s2 2s2 2p4
IE drop  from N to O
Electron in p sublevel of B
– further away from nucleus
2 electrons in same p orbital
- Greater e/e repulsion
Weak electrostatic force attraction
between nucleus and electron
Easier to remove e
IE - Low 
IE - Low 
period 2
1s2 2s2 2p5
1s2 2s2 2p6

6. IE drop from Mg to AI and P to S
Ionization Energy- Period 3
Why IE increases across the period 3?
IE increases across period 3
Nuclear charge increase 
Strong electrostatic forces
attraction bet nucleus and e
IE – High 
Na
Mg
AI
Si
P
S
CI
Ar
3p
3s
[Ne] 3s1
[Ne] 3s2
[Ne] 3s2 3p1
[Ne] 3s2 3p2
IE drop  from Mg to AI
[Ne] 3s2 3p3
[Ne] 3s2 3p4
IE drop  from P to S
Electron in p sublevel of AI
– further away from nucleus
2 electrons in same p orbital
- Greater e/e repulsion
Weak electrostatic force attraction
between nucleus and electron
Easier to remove e
IE - Low 
IE - Low 
Period 3
[Ne] 3s2 3p5
[Ne] 3s2 3p6

7. IE for Period 2 and 3
Ionization Energy- Period 2 and 3
Why IE period 3 lower than 2?
Period 3 – 3 shells/energy level
Period 3
Valence e further from nucleus
High shielding effect – more inner e
Weaker electrostatic forces
attraction bet nucleus and e
IE – Lower 
period 2
Li
Be
B
C
N
O
F
Ne
2p
2s
1s
1s2 2s1
1s2 2s2
1s2 2s2 2p1
1s2 2s2 2p2
1s2 2s2 2p3
1s2 2s2 2p4
1s2 2s2 2p5
1s2 2s2 2p6
Period 3
Na
Mg
AI
Si
P
S
[Ne] 3s2 3p1
[Ne] 3s2 3p2
[Ne] 3s2 3p3
[Ne] 3s2 3p4
CI
Ar
3rd level
3p
3s
2p
2s
1s
[Ne] 3s1
[Ne] 3s2
[Ne] 3s2 3p5
[Ne] 3s2 3p6

8. IE for Ne and Ar
Ionization Energy- Period 2 and 3
Why Ne and Ar have HIGH IE ?
Full electron configuration, 2.8/2.8.8
neon
argon
Most energetically stable structure
Difficult to lose electron
IE – High 
period 2
Li
Be
B
C
N
O
F
Ne
2p
2s
1s
1s2 2s1
1s2 2s2
1s2 2s2 2p1
1s2 2s2 2p2
1s2 2s2 2p3
1s2 2s2 2p4
1s2 2s2 2p5
1s2 2s2 2p6
Period 3
Na
Mg
AI
Si
P
S
[Ne] 3s2 3p1
[Ne] 3s2 3p2
[Ne] 3s2 3p3
[Ne] 3s2 3p4
CI
Ar
3p
3s
2p
2s
1s
[Ne] 3s1
[Ne] 3s2
[Ne] 3s2 3p5
[Ne] 3s2 3p6

9. Atomic Radius
Distance between nucleus and outmost electrons.
Atomic radius
✗
✔
Atom not like a ball – can’t measure its radius directly
Uncertain about position of electron – uncertain of atomic radius
Uncertain abt electron position
How to measure atomic radius?
Half the distance bet nuclei of two closest identical atoms.
Atomic Radius
Covalent Molecule
Noble gas
Monoatomic atoms
Depend on type of bonding – covalent or metallic
Metallic elements
Ionic compounds
½ bond length
½ bond length
½ bond length
Covalent Radius
½ bond length of 2 atom
Van Der Waals radius
½ bond length of nuclei atoms
not bonded together (noble gas)
Click here video on atomic radius
Metallic radius
½ bond length bet nuclei of
neighbouring metal ions
Click here video on atomic radius
Ionic radius
Measure indirectly using
internucleus distance
Click here video on atomic radius

10. Effective Nuclear Charge (ENC)/(Zeff)
• Screening effect/shielding
• Effective nuclear charge (ENC)/(Zeff)
(Zeff) = Nuclear charge (Z) – shielding effect
• Net positive charge felt by valence electrons.
Effective nuclear charge
Effective nuclear charge
magnesium (2.8.2)
net +2
10 inner electron shield 12+ protons
Valence electron feel a net (12-10 = +2)
Calculate Z(eff) and atomic radius for Li
Effective nuclear charge, (Zeff) = +2
1
2
Calculate Z(eff) for Li
Formula
ionization energy
Fcentripetal  Fcoulomb
Lithium (2.1)
 Z2 
IE  1312 2 
n 
 
2nd energy level
n=2
 Z2 
521  1312 2 
2 
 
Z eff  1.26
1st IE Li = 521kJ/mol
2 inner electron shield 3+ protons
Calculate atomic radius Li using Z(eff)
R
mv 2 kqZ
 2
r
R
2
mh
kqZ

m2 2 R 2
R
h2
R
m 2 kqZ
R  168pm
h
h
 
p mv
h
v
m
v
h
mR
2nd energy level
n=2
n2
2  2R
  R
m = mass electron -9.1 x 10-31
h = plank constant – 6.626 x 10-34
k = coulomb constant – 9.0 x 109
q = charge electron – 1.6 x 10-19
Z = effective nuclear charge - +1.26
Valence electron felt a net (3-2) = +1
Z(eff) = +1.26 NOT +1
(calculation shown above)
Click here video ENC Li
Click here video calculating radius Li

11. Atomic Radius (Covalent radius)
Atomic Radius- Period 2/3
Why atomic radius decrease across period 2/3
Atomic radius decrease across period 2/3
Effective Nuclear charge increase 
Strong electrostatic forces
attraction bet nucleus and e
Size decrease 
Gp 17
Li
+3
Be
+4
C
+6
N
+7
F
+9
O
+8
Effective Nuclear charge increase 
period 2
Na
+11
period 3
B
+5
Mg
+12
AI
+13
Si
+14
P
+15
S
+16
CI
+17
Effective Nuclear charge increase 
Why atomic radius increase down Gp 17?
Screening/shielding effect increase 
Inner shell electrons
electron electron repulsion increase 
Number shell increase 
Valence e further away from nucleus
Atomic radius High 

12. Positive Ions (+)
Atomic and Ionic Radius- Period 2/3
Ionic radii Positive ion (+) smaller
Negative Ions (-)
Ionic radii Negative ion (-) bigger
Decrease in number of shells – loss of electron
Increase in number of shells – gain of electron
Less  electron electron repulsion
Increase  electron electron repulsion
Size decrease 
Size increase 
Comparison bet atomic/ionic radii
Comparison bet atomic/ionic radii
Ionic radii
Ionic radii
Atomic radii
Atomic radii
Na
Mg
AI
2.8.1
2.8.2
2.8.3
Na+
2.8
Mg2+
2.8
AI3+
2.8
Atomic radii
- 3 shells
Ionic radii
- 2 shells
S
2.8.6
S2-
2.8.8
Atomic radii
CI
2.8.7
CI-
2.8.8
- 3 shells
Ionic radii
- 2 shells

13. Electronegativity
Electronegativity (EN)
Tendency of atom to attract/pull shared/bonding electron to itself
EN value higher – pull/attract electron higher (EN value from 0.7 – 4)
•
•
Shared electron cloud closer to O
•
•
EN highest
EN lowest
•
•
Electronegativity
EN increase up a Group
EN increase across a Period
Size
Factors affecting EN value
Size of atom/distance – small size/distance – stronger attraction for electron
Nuclear charge – higher nuclear charge – stronger attraction for electron
Gp 17
EN decrease  down gp 17
F
Size increase 
Nuclear charge
CI
Attraction electron decrease 
EN increase  across period 2
Li
+3
EN lower 
Be
+4
B
+5
C
+6
N
+7
O
+8
Br
F
+9
Period 2
I
EN increase  across period 2
Nuclear charge increase 
Strong attraction for electron 
EN increase 

14. •
•
Melting point across Period 2/3
Melting point down Gp 1/17
Melting Point
•
•
Temp when solid turn to liquid (temp remain constant)
Energy absorb to overcome forces attraction bet molecule
Period 2/3
Melting Point
Gp 1
Gp 17
Factors affecting melting point
Type of bonding/forces
Structure
Metallic/Non Metallic
structure
Covalent
structure
Simple molecular
structure
Ionic
structure
Metallic Bonding
Melting point across Period 2 and 3
Giant molecular
structure
period 2
C
period 3
B
Si
Be
Mg
Li
Na
N O F Ne
AI
P S
Covalent Bonding
CI
Ionic Bonding

15. Melting point for metallic/non metallic
Melting point across Period 2
Melting Point
C
period 2
B
Be
Li
N O F Ne
Li
Be
B
C
N
O
F
Ne
m/p
(/C)
180
1280
2300
3730
-210
-218
-220
-249
structure
metallic
metallic
Giant
covalent
Giant
covalent
Simple
molecular
Simple
molecular
Simple
molecular
metallic
metallic
Giant
covalent
Giant
covalent
Simple
covalent
Simple
covalent
Simple
covalent
Across period 2
m/p increase from Li – C
m/p drop from N – Ne
Metallic – non metallic
Mono
atomic
bonding
•
•
•
Simple
covalent
Metallic bonding
Giant covalent
Simple covalent
Van der waals forces bet molecules
Strong attraction bet
nucleus with sea of electrons
High m/p
Macromolecular structure with
strong covalent bonds
Highest m/p 
Simple molecular weak Van Der Waals
forces attraction bet molecules
Low m/p 

16. Melting point for metallic/non metallic
Melting point across Period 3
Melting Point
Period 3
Si
Mg AI
Na
Na
Mg
P S
AI
CI Ar
Si
P
S
CI
Ar
m/p
(/C)
98
650
660
1423
44
120
-101
-189
structure
metallic
metallic
metallic
Giant
covalent
Simple
molecular
Simple
molecular
Simple
molecular
metallic
metallic
metallic
Giant
covalent
Simple
covalent
Simple
covalent
Simple
covalent
Across period 3
m/p increase from Na – Si
m/p drop from P – Ar
Metallic – non metallic
Mono
atomic
bonding
•
•
•
Simple
covalent
Metallic bonding
Giant covalent
Simple covalent
Van der waals forces between molecules
Strong attraction bet nucleus
with sea of electrons
High m/p
Macromolecular structure
with strong covalent bonds
Highest m/p 
Simple molecular weak Van Der Waals
forces attraction bet molecules
Low m/p 

17. Atomic Radius- Group 1 and 17
Ionization Energy – Group 1 and 17
Atomic Radius
Atomic Radius
Atomic Radius
Gp 1
shell
Melting point – Group 1 and 17
Atomic Radius
Ionization Energy
Gp 17
shell
Melting point
Gp 1
Gp 17
Gp 1
Gp 17
Li
F
Li
2.1
F
2.7
Li
F
Na
2.8.1
CI
2.8.7
Na
CI
Na
CI
K
2.8.8.1
2.8.18.7
K
Br
K
Br
Rb
I
Rb
2.8.8.18.1
Br
2.8.18.18.7
I
Why atomic radius increase ?
Number shell increase 
Valence e further away from nucleus
Atomic radius High 
Rb
I
IE decrease  down group
Number shell/energy level increase 
Valence e further away from nucleus
Weak forces attraction bet nucleus and e
IE – Low 
m/p  down Gp 1
Size increase 
Attraction bet nucleus and
sea electrons decrease 
Metallic bonding 
Melting point 
m/p  increase Gp 17
Size increase 
VDF increase 
IMF attraction bet
molecules increase 
Melting point 