2: Bonding and Structure Flashcards
Definition of ionic bonding
The electrostatic attraction between oppositely charged ions
Factors affecting the strength of ionic bonding
- Difference in charges (greater difference means stronger bonds)
- Atomic radius (shorter means stronger bonds)
Trend in ion size down a group
-Size of ion increase as the charges remain the same but their are more electrons
Definition of isoelectronic ions
Ions with the same number of electrons (e.g N3-, O2-, F-)
Factor affecting size of isoelectronic ions
-As the charge is the same the size is only determined by the nuclear charge
Physical evidence for ions
- High MP/BP indicate strong electrostatic forces between oppositely charged ions
- Conductivity of electricity when molten/in solution indicates presence of mobile charge carrying particles in the substance
- Migration of ions in electrolysis shows positive and negative ions
Definition of covalent bonding
The electrostatic attraction between a shared pair of electrons and the nuclei of each atom
Bond angle in a linear molecule
180°
Bond angle in trigonal planar
120°
Bond angle in tetrahedral
109.5°
Bond angle in a bent molecule
104.5
Bond angle in tetrahedral with 1 lone pair
107.5
Electronegativity definition
The ability of an atom with a covalent bond to attract the bonding pair of electrons
Test if a molecule is electronegative
A jet of the substance would be deflected by a charged rod
What are London forces
The attraction between instantaneous dipoles in molecules
How do instantaneous dipoles form
- As electrons are constantly moving there can be more electrons on one side of the molecule than the other, creating an instantaneous dipole
- When a dipole moves near to another molecule it will attract/repel electrons, and induce a dipole in the second molecule
Factor affecting strength of London forces
Strength increases as the number of electrons in the molecule increases
What is dipole-dipole attraction?
The attraction between oppositely charged dipoles of different polar molecules
What is hydrogen bonding?
The attraction between an exposed hydrogen atom and an element with a lone electron pair
Requirements for hydrogen bonding
A hydrogen atom directly bonded to N/O/F within a polar molecule
Why is the hydrogen atom exposed in hydrogen bonding?
The N/O/F is so electronegative that it draws the electron pair towards itself, effectively leaving an exposed proton
Why does water have a relatively high MP/BP
The molecules can form two hydrogen bonds per molecule
Why does water expands when it freezes
The hydrogen bonds pull the water molecules into fixed positions in a lattice structure
Trend in BP of alkanes in accordance to mass
As the molecular mass increases, the number of electrons increase, so the London forces are stronger
