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
Effect on BP of branching in alkanes
Lower boiling points as it prevents the molecules from approaching each other as closely, so the induction effect is weaker and therefore the London forces are weaker
Why is the BP of alcohols higher
The OH group allows for hydrogen bonding between molecules
Trend in BP in hydrogen halides
HCl → HBr → HI → HF
Explanation for trend in BP in hydrogen halides
As the molecules increase in size there are more electrons so the London forces are stronger, however there is hydrogen bonding in HF
What is hydration of ions
- Oxygen in water molecules is attracted to cations
- Hydrogen in water molecules is attracted to anions
- This causes water molecules to link to the ions
- As the water molecules are vibrating, they shake the ion apart
- Some ionic compounds don’t dissolve as the electrostatic attraction is too great
Definition of metallic bonding
The electrostatic attraction between the metal cations and the delocalised electron region
