ib chemistry on periodic trends, effective nuclear charge and physical properties
DESCRIPTION
IB Chemistry on Periodic Trends, Effective Nuclear Charge and Physical properties.TRANSCRIPT
Periodic Table of elements – divided to Groups, Periods and Blocks
Group 1 18
Groups – Vertical column • Same number of valence electron • Same number outmost electrons
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
Period- Horizontal row • 7 periods/row • Same number of shell
Periods 1 7
s block - s orbitals partially fill
d block • d orbitals partially fill
f block • f orbital partially fill
p block • p orbital partially fill
Excellent site from periodic videos Click here to view
Periodic Table – s, p d, f blocks elements s block elements • s orbitals partially fill
p block elements • p orbital partially fill
d block elements • d orbitals partially fill • transition elements
1 H 1s1
2 He 1s2
11 Na [Ne] 3s1
12 Mg [Ne] 3s2
5 B [He] 2s2 2p1
6 C [He] 2s2 2p2
7 N [He] 2s2 2p3
8 O [He] 2s2 2p4
9 F [He] 2s2 2p5
10 Ne [He] 2s2 2p6
13 Al [Ne] 3s2 3p1
14 Si [Ne] 3s2 3p2
15 P [Ne] 3s2 3p3
16 S [Ne] 3s2 3p4
17 CI [Ne] 3s2 3p5
18 Ar [Ne] 3s2 3p6
19 K [Ar] 4s1
20 Ca [Ar] 4s2
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
n = 2 period 2
3 Li [He] 2s1
4 Be [He] 2s2
Click here video s,p,d,f blocks, Click here video on s,p,d,f notation Click here electron structure
Video on electron configuration
f block elements • f orbitals partially fill
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.
Chemical change – diff composition from original substances - chemical bonds broken/ formed - new products formed
Element properties Atomic properties
• Color, texture, odor • Density, hardness, ductility • Brittleness, Malleability • Melting /boiling point • Solubility, polarity
• Ionization energy • Atomic radii • Ionic radii • Electronegativity
Periodic Trends • Across period 2/3 • Down group 1/17
Gp 1 Gp 17
period 3
period 2
Ionization energy
Atomic/ionic radii
Melting point
Electronegativity
Factors affecting ionization energy
Distance from nucleus Nuclear charge
Ionization energy (IE)
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
1st Ionization energy Min energy to remove 1 mole e from 1 mole of element in gaseous state M(g) M+ (g) + e
Ionization energy
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
electron
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.
Why IE increases across the period? Why IE decreases down a group ?
1 2 3
Higher electron/electron repulsion
Easier valence e to leave
IE – Low
Inner electron – shield valence e from positive nuclear charge
Strong electrostatic forces attraction bet nucleus and e
IE – High
Distance near Nuclear charge
Strong electrostatic forces attraction bet nucleus and e
IE – High
+3 +4 +5 +6
Nuclear charge increase
+6
Why IE increases across the period 2? IE drop from Be to B and N to O
IE increases across period 2
Nuclear charge increase
Strong electrostatic forces attraction bet nucleus and e
IE – High
1s
2p
2s
1s2 2s1 1s2 2s2 1s2 2s2 2p1 1s2 2s2 2p2 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p5 1s2 2s2 2p6
Li Be B C N O F Ne
period 2
IE drop from Be to B IE drop from N to O
Electron in p sublevel of B – further away from nucleus
Weak electrostatic force attraction between nucleus and electron
IE - Low
2 electrons in same p orbital - Greater e/e repulsion
Easier to remove e
IE - Low
Ionization Energy- Period 2
Why IE increases across the period 3? IE drop from Mg to AI and P to S
IE increases across period 3
Nuclear charge increase
Strong electrostatic forces attraction bet nucleus and e
IE – High
3s
3p
[Ne] 3s1 [Ne] 3s2 [Ne] 3s2 3p1
Na Mg AI Si P S CI Ar
Period 3
IE drop from Mg to AI IE drop from P to S
Electron in p sublevel of AI – further away from nucleus
Weak electrostatic force attraction between nucleus and electron
IE - Low
2 electrons in same p orbital - Greater e/e repulsion
Easier to remove e
IE - Low
Ionization Energy- Period 3
[Ne] 3s2 3p2 [Ne] 3s2 3p3 [Ne] 3s2 3p4 [Ne] 3s2 3p5 [Ne] 3s2 3p6
Period 3 – 3 shells/energy level
Valence e further from nucleus
Weaker electrostatic forces attraction bet nucleus and e
IE – Lower
1s
2p
2s
1s2 2s1 1s2 2s2 1s2 2s2 2p1 1s2 2s2 2p2 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p5 1s2 2s2 2p6
Li Be B C N O F Ne
Ionization Energy- Period 2 and 3 Why IE period 3 lower than 2? IE for Period 2 and 3
period 2
Na
1s
2s
2p
3s
3p
[Ne] 3s1
Mg AI Si P S CI Ar
Period 3
[Ne] 3s2 3p1 [Ne] 3s2 [Ne] 3s2 3p2 [Ne] 3s2 3p3 [Ne] 3s2 3p4 [Ne] 3s2 3p5 [Ne] 3s2 3p6
High shielding effect – more inner e Period 3
3rd level
Full electron configuration, 2.8/2.8.8
Most energetically stable structure
Difficult to lose electron
IE – High
1s
2p
2s
1s2 2s1 1s2 2s2 1s2 2s2 2p1 1s2 2s2 2p2 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p5 1s2 2s2 2p6
Li Be B C N O F Ne
Ionization Energy- Period 2 and 3 Why Ne and Ar have HIGH IE ? IE for Ne and Ar
period 2
Na
1s
2s
2p
3s
3p
[Ne] 3s1
Mg AI Si P S CI Ar
Period 3
[Ne] 3s2 3p1 [Ne] 3s2 [Ne] 3s2 3p2 [Ne] 3s2 3p3 [Ne] 3s2 3p4 [Ne] 3s2 3p5 [Ne] 3s2 3p6
neon
argon
Atomic Radius
How to measure atomic radius?
Atom not like a ball – can’t measure its radius directly Uncertain about position of electron – uncertain of atomic radius
✗
✔
Distance between nucleus and outmost electrons. Atomic radius
Uncertain abt electron position
Depend on type of bonding – covalent or metallic
Half the distance bet nuclei of two closest identical atoms.
Atomic Radius
Covalent Molecule Noble gas Monoatomic atoms
Metallic elements Ionic compounds
½ bond length
Covalent Radius
½ bond length of 2 atom
½ bond length
Van Der Waals radius
½ bond length of nuclei atoms not bonded together (noble gas)
½ bond length bet nuclei of neighbouring metal ions
Ionic radius
Measure indirectly using internucleus distance
Metallic radius
½ bond length
Click here video on atomic radius Click here video on atomic radius Click here video on atomic radius
Click here video calculating radius Li
Effective nuclear charge
Click here video ENC Li
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 magnesium (2.8.2)
10 inner electron shield 12+ protons
Calculate Z(eff) for Li
Effective nuclear charge, (Zeff) = +2
Valence electron feel a net (12-10 = +2)
net +2
Z(eff) = +1.26 NOT +1 (calculation shown above)
1st IE Li = 521kJ/mol
2
2
21312521
Z
26.1effZ
2 inner electron shield 3+ protons
Valence electron felt a net (3-2) = +1
Calculate atomic radius Li using Z(eff)
Formula ionization energy coulomblcentripeta FF
2
2
R
kqZ
r
mv
mv
h
p
h
Rm
hv
R
R
n
22
2
R
kqZ
Rm
mh
222
2
kqZm
hR
2
2
m
hv
2nd energy level n=2
pmR 168
2nd energy level n = 2
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
R
1 2
Lithium (2.1)
Calculate Z(eff) and atomic radius for Li
2
2
1312n
ZIE
Effective Nuclear charge increase
Why atomic radius decrease across period 2/3 Atomic Radius (Covalent radius)
Atomic radius decrease across period 2/3
Effective Nuclear charge increase
Strong electrostatic forces attraction bet nucleus and e
Size decrease
Li
period 2
Atomic Radius- Period 2/3
Be
+4 B
+5 C
+6 N
+7 +3 O
+8
F
+9
Effective Nuclear charge increase
period 3
Na
+11
Mg
+12
AI
+13 Si
+14 P
+15 S
+16
CI
+17
Gp 17
Number shell increase
Valence e further away from nucleus
Atomic radius High
Why atomic radius increase down Gp 17?
Screening/shielding effect increase
Inner shell electrons electron electron repulsion increase
Ionic radii
2.8.8 2.8.8 - 2 shells
2.8.6 2.8.7 - 3 shells
2.8 2.8 2.8 - 2 shells
2.8.1 2.8.2 2.8.3 - 3 shells
Atomic and Ionic Radius- Period 2/3 Positive Ions (+) Negative Ions (-)
Ionic radii Positive ion (+) smaller
Comparison bet atomic/ionic radii
Decrease in number of shells – loss of electron
Less electron electron repulsion
Size decrease
Atomic radii
Ionic radii
Ionic radii Negative ion (-) bigger
Increase in number of shells – gain of electron
Increase electron electron repulsion
Size increase
Comparison bet atomic/ionic radii
Atomic radii
Ionic radii
Na
Na+
Mg
Mg2+
AI
AI3+
Atomic radii
Ionic radii
AI S CI
S2- CI-
Atomic radii
Period 2
Shared electron cloud closer to O
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)
EN highest EN lowest
Factors affecting EN value • Size of atom/distance – small size/distance – stronger attraction for electron • Nuclear charge – higher nuclear charge – stronger attraction for electron
Electronegativity • EN increase up a Group • EN increase across a Period
F
CI
Br
I
Size increase
Attraction electron decrease
EN lower
Size
Be
+4
Li
+3 B
+5 N
+7
O
+8 F
+9
EN increase across period 2
Nuclear charge
EN increase across period 2 Nuclear charge increase Strong attraction for electron
EN increase
Gp 17
C
+6
EN decrease down gp 17
Melting Point • Temp when solid turn to liquid (temp remain constant) • Energy absorb to overcome forces attraction bet molecule
Factors affecting melting point
• Melting point across Period 2/3 • Melting point down Gp 1/17
Gp 1 Gp 17
Period 2/3
Structure
Metallic/Non Metallic structure
Covalent structure
Giant molecular structure
Type of bonding/forces
Ionic Bonding Covalent Bonding Ionic structure
Simple molecular structure
Metallic Bonding
Melting Point
period 2
period 3
Li
Be
B
C
N O F Ne
Na
Mg AI
Si
P S CI
Melting point across Period 2 and 3
Melting Point Melting point across Period 2
period 2
Van der waals forces bet molecules
Across period 2 • m/p increase from Li – C • m/p drop from N – Ne • Metallic – non metallic
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
Mono atomic
bonding metallic metallic Giant covalent
Giant covalent
Simple covalent
Simple covalent
Simple covalent
Simple covalent
Li
Be
B
C
N O F Ne
Metallic bonding Giant covalent Simple covalent
Strong attraction bet nucleus with sea of electrons
Macromolecular structure with strong covalent bonds
Simple molecular weak Van Der Waals forces attraction bet molecules
Melting point for metallic/non metallic
High m/p Highest m/p Low m/p
Melting Point Melting point across Period 3
Period 3
Van der waals forces between molecules
Across period 3 • m/p increase from Na – Si • m/p drop from P – Ar • Metallic – non metallic
Na Mg AI 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
Mono atomic
bonding metallic metallic metallic Giant covalent
Simple covalent
Simple covalent
Simple covalent
Simple covalent
Na
Mg AI
Si
CI Ar
Metallic bonding Giant covalent Simple covalent
Strong attraction bet nucleus with sea of electrons
Macromolecular structure with strong covalent bonds
Simple molecular weak Van Der Waals forces attraction bet molecules
Melting point for metallic/non metallic
High m/p
P S
Highest m/p Low m/p
Valence e further away from nucleus Weak forces attraction bet nucleus and e
Number shell/energy level increase
Melting point – Group 1 and 17
IE decrease down group
IE – Low
Atomic Radius
Gp 1
Na
Li
K
Rb
Gp 17
F
CI
Br
I
2.1
2.8.1
2.8.8.1
2.8.8.18.1
shell shell
2.7
2.8.7
2.8.18.7
2.8.18.18.7
Atomic Radius
Atomic Radius- Group 1 and 17 Ionization Energy – Group 1 and 17
Why atomic radius increase ?
Number shell increase
Valence e further away from nucleus
Atomic radius High
Gp 17 Gp 1
Li
Na
K
Rb
F
CI
Br
I
Melting point Ionization Energy
Atomic Radius Atomic Radius
Rb
K
Na
Li
I
Br
CI
F
Gp 1 Gp 17
m/p down Gp 1 m/p increase Gp 17
Metallic bonding Melting point
Attraction bet nucleus and sea electrons decrease
Size increase Size increase VDF increase
IMF attraction bet molecules increase
Melting point