chemistry - periodicity
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CHEMICAL PERIODICITY
Zeff = Z –
σ
PHYSICAL PROPERTIES Property Atomic radii decrease across a period Atomic radii increase descending a group From Na to Al, the size of the cation is always smaller than the parent atom From P to Cl, the size of the anion is always larger than the parent atom Size of isoelectronic ions decrease across a period For more information st 1 IE decreases descending a group
Explanation Zeff increases across a period. The number of protons, and thus Z, increases, while σ remains approximately constant as the number of fully filled inner principle quantum shells remain the same Zeff decreases descending a group. The number of protons, and thus Z, increases, while σ increases as the number of fully filled inner principle quantum shells increases The Zeff increases from Na to Al as the cation has one less shell of electrons, Consequently, the nucleus exerts a greater attractive force on the valence electrons in the cation. Both the anion and its parent atom have the same number of protons, making Z identical. The anion however, has more electrons that its parent atom, making the nucleus attract the valence electron less strongly in the anion σ remains constant as the have the same number of inner electrons. Z increases, and thus the nucleus attracts the valence electrons more strongly about ionization energy, refer to the atomic structure cheatsheet Zeff decreases descending a group. Z increases descending a group while σ increases as well, but more significantly
CHEMICAL PROPERTIES
g I n p i c Na G u d e r y l g I I n o Mg p r G t S I I I p G
Al
y l k V I a e p W Si G g n i c u d e r
Reaction with dry oxygen and heat
Reaction with dry chlorine and heat
Reaction with water
pH in water
4Na + O2 2Na2O Vigorous
2Na + Cl2 2NaCl Very vigorous
2Na + 2H2O 2NaOH + H2 Violent reaction with cold water
13
2Mg + O2 2MgO Very vigorous
Mg + Cl2 MgCl2 Vigorous
Mg + H2O MgO + H2 Vigorous reaction with steam
9
4Al + 2O2 2Al2O3 Vigorous initially
2Al + 3Cl2 3AlCl3 Vigorous
2Al + 3H2O Al2O3 + 3H2 Vigorous reaction with steam
7
No reaction
7
Si + O2 SiO2 Slow
AlCl3 may dimerize
Si + 2Cl2 SiCl4 Slow
OXIDES + PROPERTIES Oxide
Na2O
MgO
Oxidation number
+1
+2
No. of valence e -
1
pH of solution
Oxide &hydroxide
+3
+4
2
3
4
P4O6 P4O10 + 3 , +5
SO2 SO3 +4, +6
Cl2O (ClO2) Cl2O7 +1, +4. +7
Ionic Giant ionic lattices Solid
Giant covalent
High bp due to large amount of energy required to break ionic bonds in the lattice (Na, Mg, Al) or giant covalent structure (Si)
6
7
Good
12
Sparingly soluble 9
Strongly alkaline
Weakly alkaline
Na2O(s) + H2O(l) 2NaOH(aq)
MgO(s) + H2O(l) Mg(OH)2(aq)
Basic; Hydroxides are strongly alkaline
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Covalent Simple molecular Gas, solid
Gas, (liquid) liquid
No conductivity
No charged particles
Insoluble
Gas, liquid Weak VDW forces
Very poor
Mobile ions present in molten state
Soluble
5
Multiple oxidation numbers. Atoms have unoccupied, low-lying 3d orbitals that can be used to expand their octet
Oxidation number equal number of valence e -
Molten electrical conductivity Solubility in water
SiO2
Always positive: Oxygen is more electronegative
Bonding Structure State at 20°C
Al2O3
No mobile ions in liquid state
React with water to form strongly acidic solutions
Lattice energy highly exothermic
2 Strongly acidic
Please don’t memorize these equations. Remember: oxidation states don’t change on either side. Write the reactants product, and then balance all non-O and non-H elements and finally balance with water.
Amphoteric
P4O6(g) + 6H2O(l) 4H3PO3(aq) P4O10(g) + 6H2O(l) 4H3PO4(aq)
SO2(g) + H 2O(l) H2SO3(aq) SO3(l) + H2O(l) H2SO4(aq) Acidic
Cl2O(g) + H2O(l) 2HClO(aq) Cl2O7(l) + H2O(l) 2HClO4(aq)
acid-base behaviour
) q a ( l C H 2 + ) s ( O 2 a N ) l ( O 2 H + ) q a ( l C a N 2
) q a ( l C H + ) q a ( H O a N O 2 H + ) q a ( l C a N
) q a ( l C H 2 + ) s ( O g M ) l ( O 2 H + ) q a ( 2 l C g M 2
) q a ( 3
O N H 2 + ) q a ( 2 ) H O ( g M ) l ( O 2 H 2 + ) q a ( 2 ) 3 O N ( g M
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) q a ( l C H 6 + ) s ( 3
O 2 l A ) l ( O 2 H 3 + ) q a ( 3 l C l A
O 2 H 3 + ) q a ( H O a N 2 + ) s ( 3
O 2 l A ) q a ( ] 4 ) H O ( l A [ + a N 2
) q a ( H O a N 2 + ) s ( 2
O i S ) l ( O 2 H + ) q a ( 3 O i S 2 a N
) q a ( H O a N 2 1 + ) g ( 6
O 4 P ) l ( O 2 H 6 + ) q a ( 3 O P 3 a N 4
) q a ( H O a N 2 1 + ) g ( 0 1
O 4 P ) l ( O 2 H 6 + ) q a ( 4 O P 3 a N 4
) q a (
H O a N 2 + ) g ( 2
O S ) l ( O 2 H + ) q a ( 3 O S 2 a N
) q a ( H O a N 2 + ) l ( 3 O S ) l ( O 2 H + ) q a ( 4 O S 2 a N
) q a ( H O a N 2 + ) g ( O 2 l C ) l ( O 2 H + ) q a ( O l C a N 2
) q a ( H O a N 2 + ) g ( 7
O 2 l C ) l ( O 2 H + ) q a ( 4 O l C a N 2
CHLORIDES + PROPERTIES Oxide
NaCl
MgCl2
+1
+2
AlCl3
SiCl4
+3
+4
PCl3 PCl5 +3, +5
SCl2 S2Cl2 +1 , +2
Atoms have unoccupied, low-lying 3d orbitals
Does not form SCl 6 due to steric hindrance
Always positive: Chlorine is more electronegative electronegative
Oxidation number
Oxidation number equal number of valence e -
Simple molecular Structure State at 20°C Molten electrical conductivity
Giant ionic lattice
Very poor
Good Mobile ions present in molten state
Conducts electricity in aqueous solution
Dissolves 7
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Simple molecular Liquid
Solid Na, Mg: Large amount of energy required to break ionic bonds
Solubility in water pH
Comparable enegativities of Al and Cl
Liquid, gas Weak VDW forces
No conductivity No mobile ions in liquid state
Dissolves to evolve HCl fumes 6.5
3
2
Slightly acidic
Strongly acidic
Strongly acidic
Liquid, gas
Equations
-
) q a ( l C 2 + ) q a ( + 2 ] 6 ) O 2 H ( g M [
) l ( O 2 H 6 + ) s ( 2 l C g M
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) l ( O 2 H 6 + ) s ( 3 l C l A ) q a ( l C 3 + ) q a ( + 3 ] 6 ) O 2 H ( l A [
) l ( O 2 H 2 + ) l ( 4 l C i S ) g ( l C H 4 + ) s ( 2
O i S
) l ( O 2 H 3 + ) l ( 3 l C P ) g ( l C H 3 + ) q a ( 3 O P 3 H
) l ( O 2 H 4 + ) l ( 5 l C P ) g ( l C H 5 + ) q a ( 4 O P 3 H
) l ( O 2 H 2 + ) l ( 2 l C 2 S 2 ) g ( l C H 4 + ) q a ( 2
O S + ) s ( S 3
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