Periodicity 4
Selected Trends Across Period 3
IB Topic 3.3 and 13.1 (selected parts)
Reference: Higher Level Chemistry, p. 86 and p. 89
Review: Structure and Bonding
If you want to predict the PROPERTIES of a substance,
then you must first be able to describe its
“structure and bonding”.
types of particles
chemical bonds
(intramolecular forces)
organization of particles
intermolecular forces
Review: Structure and Bonding
Ionic Compounds
types of particles = positive ions and negative ions
organization of particles (e.g. NaCl) = crystal lattice structure
= every Na+ ion is surrounded by 6 Cl– ions
= every Cl– ion is surrounded by 6 Na+ ions
chemical bonds (intramolecular forces) = ionic bonds
“intermolecular” forces = ionic bonds / forces of attraction
Review: Structure and Bonding
Metallic Compounds
types of particles = metallic cations (+) & delocalized electrons
organization of particles
= metal cations are in a lattice structure (solids)
= valence electrons are shared between all cations
chemical bonds (intramolecular forces) = metallic bonds
“intermolecular” forces = metallic bonds
Review: Structure and Bonding
Giant / Network
Covalent Solids
types of particles = atoms (carbon, or silicon, or silicon + oxygen)
organization of particles
= atoms are arranged in rigid 3-D lattice structures
= exact pattern depends on the substance
(diamond vs graphite vs C60 vs silicon vs silicon dioxide (SiO2)
chemical bonds (intramolecular forces) = covalent bonds (non-polar)
“intermolecular” forces = covalent bonds (non-polar)
Review: Structure and Bonding
Covalent Molecular
Substances (non-polar)
types of particles = non-polar covalent molecules (no dipoles)
organization of particles
= random arrangement in gases and liquids, limited
structure in solids
chemical bonds (intramolecular forces) = covalent bonds (non-polar or polar)
“intermolecular” forces = van der Waals / dispersion forces
Review: Structure and Bonding
Covalent Molecular
Substances (polar)
∂+
∂–
∂+
∂+
∂–
∂+
∂–
∂–
∂+
types of particles = polar covalent molecules
organization of particles
= defined arrangement in solids so that opposite
dipoles attract; more random arrangement in gases
chemical bonds (intramolecular forces) = covalent bonds (polar)
“intermolecular” forces = dipole-dipole force
OR hydrogen bonds (F,O,N – H)
∂–
Review: Structure and Bonding
REVIEW: Electrical Conductivity
Substances conduct electricity when electrons or charges
can flow from one point to another.
metals:
delocalized valence
electrons move through the
solid ∴ a conductor
covalent compounds:
all types: no mobile ions or
electrons ∴ not a conductor
ionic compounds:
solids: + and – ions are fixed ∴ not a conductor
liquids: + and – ions are mobile ∴ a conductor
Review: Structure and Bonding
REVIEW: Bonding Continuum
The type of bond in a compound may be predicted on the basis of
the electronegativity difference between the two bonded atoms.
∆EN
0
0.3
1.7
pure
(nonpolar)
covalent
bond
polar
covalent
bond
equal
sharing
of
electrons
unequal
sharing
of
electrons
ionic bond
transfer
of
electrons
Bonding in Period 3 Oxides
Assessment Statement 3.3.2
Discuss the changes in nature,
from ionic to covalent
and from acidic to basic,
of the oxides across Period 3.
next year
Bonding in Period 3 Oxides (I)
sodium oxide
magnesium
oxide
aluminum
oxide
silicon oxide
formula
Na2O
MgO
Al2O3
SiO2***
structure
ionic crystal
lattice
ionic crystal
lattice
ionic crystal
lattice
giant covalent
∆EN
3.4 - 0.9
= 2.5
3.4 - 1.3
= 2.1
3.4 - 1.6
= 1.8
3.4 - 1.9
=1.5
bonding
ionic bonding ionic bonding ionic bonding
electrical
conductivity
solids - no
liquids - yes
solids - no
liquids - yes
solids - no
liquids - yes
state (under
solid
solid
solid
standard conditions)
(not molecular)
polar covalent
bonding
very poor
solid
Bonding in Period 3 Oxides (2)
phosphorus oxide
sulfur oxides
chlorine oxides
P2O5 or P4O10
SO2 / SO3
Cl2O /Cl2O7
molecular
covalent
3.4 - 2.2
= 1.2
polar covalent
bonding
molecular
covalent
3.4 - 2.6
= 0.8
polar covalent
bonding
molecular
covalent
3.4 - 3.2
= 0.2
pure covalent
bonding
electrical
conductivity
not a chance
not a chance
not a chance
state (under standard
solid
gas
gas / liquid
formula
structure
∆EN
bonding
conditions)
Bonding in Period 3 Chlorides
Assessment Statement 13.2.1
Explain the physical states (under standard conditions) and
electrical conductivity (in the molten state) of the chlorides
and oxides of the elements in period 3 in terms of their
bonding and structure.
Include these oxides:
Na2O, MgO, Al2O3, SiO2, P4O6, P4O10, SO2, SO3, Cl2O and Cl2O7.
Include these chlorides:
NaCl, MgCl2, Al2Cl6, SiCl4, PCl3, PCl5 and Cl2.
Bonding
BondingininPeriod
Period3 3Chlorides
Oxides (I)(1)
sodium
chloride
magnesium
chloride
aluminum
chloride
silicon
chloride
AlCl3
Al2Cl6*
SiCl4
formula
NaCl
MgCl2
structure
ionic crystal
lattice
ionic crystal
lattice
∆EN
3.2 - 0.9
= 2.3
bonding
ionic bonding
electrical
conductivity
solids - no
liquids - yes
state (under
solid
standard conditions)
non polar
molecular
covalent
nonpolar
molecular
covalent
3.2 - 1.6
3.2 - 1.9
= 1.6
=1.3
polar covalent polar covalent
ionic bonding
bonding
bonding
solids - no
no
no
liquids - yes
3.2 - 1.3
= 1.9
solid
solid
liquid
Bonding
BondingininPeriod
Period3 3Chlorides
Oxides (I)(2)
phosphorus
chlorides
sulfur chloride
chlorine gas
PCl3 / PCl5
S2Cl2
Cl2
structure
nonpolar
molecular
covalent
nonpolar
molecular
covalent
nonpolar
molecular
covalent
∆EN
3.2 - 2.2
= 1.0
3.2 - 2.6
= 0.6
3.2 - 3.2
=0
bonding
polar covalent
polar covalent
nonpolar covalent
electrical
conductivity
no
no
no
state (under standard
liquid / solid
liquid
gas
formula
conditions)