Topic 2 Flashcards
Isoelectronic ions
Ions of different elements with the same electronic configuration (but different ionic radii)
Covalent bond
The electrostatic attraction between 2 nuclei of 2 atoms and the shared pair of electrons between them
Polar covalent bond
Each atom does not have an equal attraction to the bonding electron pair, so there are positive and negative partial charges at the ends of the molecule
Dative covalent bond
An atom donates its lone pair of electrons to another atom/ion, forming a covalent bond in which the pair of electrons comes from one atom
Electronegativity
The tendency of an atom to attract a bonding pair of electrons
Hydrogen bond
The electrostatic attraction between the partial positive charge of a hydrogen atom and the partial negative charge of a lone pair of electrons on an atom of a neighbouring molecule
Metallic bonding
The strong electrostatic attraction between the metal cations and sea of delocalised electrons
Dipole
When two charges of equal magnitude but opposite signs are separated by a small distance
Ionic bond
The strong electrostatic attraction between oppositely charged ions
Factors affecting strength of ionic bonding
Greater charge of anion and cation.
Smaller ionic radius (less shells).
-greater charge density, higher lattice energy, stronger bond
Polyatomic
An ion with more than one atom
Trend in boiling points of G4-H molecules
Boiling point increases down group 4.
-london forces
Lower than G5/6/7 because G4-H molecules are non-polar so only have london forces.
Trend in boiling points of G5/6/7-H molecules
Decreases then increases down the group.
O,F,N form hydrogen bonds- high boiling points.
For rest, boiling point increases because of london forces.
Boiling points vs chain length
Boiling point increases as chain length increases
-london forces
Boiling points vs branching
Branching reduces the contact surface area
-reduces the number of london forces that can form
Evidence for existence of ions
Migration of ions (CuSO4, current, move towards negative)
Physical properties of ionic compounds
Why a molecule has a specific shape
X number of bonding regions around the central atom.
Repulsion between the bonding pairs of electrons.
Atoms arranged to minimise repulsion.
BeCl2 or CO2
Planar
180
Ethene
Planar
120
COH2 and BeF3
Trigonal planar
120
CH4
Tetrahedral
109.5
SF6
Octahedral
90
NH3
Trigonal pyramidal
107
PF5
Trigonal bipyramidal
120 and 90
H20
Bent
104
Why does HF form hydrogen bonds, but HBr not?
F is more electronegative than Br
Because it has less shells, so is smaller and has less electron shielding.
So HF has a greater dipole moment.
Why can propanone dissolve in many substances?
It has both polar and non polar characteristics
So it can form both hydrogen bonds (with its O atom) and london forces (with its CH3 groups)
Why is NaCl more soluble in water than hexane?
Hexane molecules can’t fit between ions in the lattice
