1b)ii) - Structure and bonding Flashcards
What are intermolecular forces acting between molecules also known as
Inter molecular forces acting between molecules are also known as Van der waals forces
What are the several types of intermolecular forces (Van der waals)
- London dispersion forces
- permanent dipole - permanent dipole interactions
- hydrogen bonding
What are London dispersion forces
London dispersion forces are forces of attraction that can operate between all atoms and molecules.
What is the strength of LDFS
London dispersion forces are much weaker than all types of bonding
What are London dispersion forces the result of
They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules
What is the strength of London dispersion forces related to
The strength of London dispersion forces is related to the number of electrons within an atom of molecule
What is the link between side of molecule and strength of LDFS
The bigger the molecule the stronger the London dispersion forces
More electrons means what in terms of London dispersion force
More electrons means stronger London dispersion force
What causes a temporary dipole
The electrons in an atom may become unevenly distributed causing a temporary dipole
When does the strength of LDFs increase
The strength of London dispersion force increases as the size of the atoms increases
When are London dispersion forces important
London dispersion forces are important in the absence of other types of attractions between molecules
When is a molecule described as polar
A molecule is described as polar if it has a permanent dipole
What is the strength of permanent dipole - permanent dipole interactions
Permanent dipole - permanent dipole interactions are stronger than London dispersion forces for molecules with similar numbers of electrons
Which bonds where a hydrogen atom bonds with an atom of strong electronegativity are highly polar
Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar
What is a hydrogen bond
Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar
What is the strength of a hydrogen bond
A hydrogen bond is stronger than other forms of intermolecular forces but weaker than a covalent bond
What are H - O bonds
The H - O bonds are polar covalent
Why is water a polar molecule
The whole water molecule is polar because it has a ‘positive end’ and a ‘negative end’
When do we say the molecule has a permanent dipole
We say the molecule has a permanent dipole if the S+ve centre and S-ve centre do not coincide
What do molecules with a permanent dipole attract
Molecules with a permanent dipole attract each other. The attraction is stronger than London dispersion forces
What is hydrogen binding an example of and what do they still include
Hydrogen bonding is a particular example of permanent dipole - permanent dipole attraction. Chemicals which have hydrogen bonding still have London dispersion forces as well
What are the melting and boiling points of polar substances compared to non polar substance with similar numbers of electrons
The melting and boiling points of polar substances are higher than the melting and boiling points of non polar substances with similar numbers of electrons
What are properties of substances that are affected by hydrogen bonding
Boiling points, melting points, viscosity and solubility /miscibility in water are properties of substances that are affected by hydrogen bonding
What happens when a molecule contains polar bonds but is symmetrical
When a molecule contains polar bonds but is symmetrical i.e tetrahedral or linear. The polarities cancel each other out and the molecule is non polar
What are ionic compounds and polar molecular compounds soluble and insoluble in
Ionic compounds and polar molecular compounds tend to be soluble in polar solvents such as water and insoluble in non-polar solvents (like dissolve like)
What are non polar molecular substances soluble and insoluble in
Non polar molecular substances tend to be soluble in non polar solvents and insoluble in polar solvents
What are key features you need to consider to predict the solubility of a compound
- presence in molecules of O - H or N - H bonds, which could result in a molecule possessing a permanent dipole
- water is a useful solvent for ionic compounds because it is polar
- the larger the molecule the stronger the intermolecular forces and therefore the higher the viscosity of the liquid (thicker the liquid)
What happens in a temporary dipole
I.e one side of the atom becomes fleetingly negative while the other side becomes positive. Which has a knock on effect on the neighbouring atoms
What are London dispersion forces caused by
They are caused by uneven distribution of electrons
Which type of ends do dipole-dipole attractions arise in
Dipole -dipole attractions arise between oppositely charged ends of DIFFERENT MOLECULES
What is important to remember about permanent - dipole to permanent - dipole attractions
THEY ARISE BETWEEN DIFFERENT MOLECULES !!!!!!
What will happen if you have a molecule which contains dipole dipole as well as LDFs
If you have an atom with LDFs and pd-pd melting and boiling point will be higher
Which type of molecules do intermolecular bonding happen between
Intermolecular bonding happen between DIFFERENT MOLECULES !!!!!!!!!!!!!!!
Which atoms are hydrogen bonds formed with
- fluorine
- oxygen
- nitrogen
What will happen to the mp/bp of a compound when hydrogen bonding is present
When H- bonding is present the compound will have a much higher melting and boiling point when compared to similar molecules
What is the mass number
The number of protons + neutrons
What is the atomic number
The number of protons
Which is stronger bonds between molecules or ions?
Bonds between molecules are weaker than bonds between ions
What does lower viscosity mean
Stronger Van der waals forces
What some elements have higher boiling points than others
- there are stronger / more Van der waals forces
- there are more electrons
- correctly identify what Van der waals forces they have
What are the anomalous boiling points of ammonia water and hydrogen fluoride a result of
The anomalous boiling points of ammonia, water and hydrogen fluoride are the result of hydrogen bonding
