unit 1 KA2 - structure and bonding Flashcards
what is a covalent bond
the result of two positive nuclei being held together by their common attraction for the shared pair of electrons. in covalent bond, atoms share pairs of electrons
when are polar covalent bonds formed
when the attraction of the atoms for the pair of bonding electrons is different
what does delta positive δ+ and delta negative δ- notation indicate
they can be used to indicate the partial charges on atoms, which give rise to a dipole
how can ionic formulae be written
giving the simplest ratio of each type of ion in the substance
what are ionic bonds
ionic bonds are the electrostatic attraction between positive and negative ions. ionic compounds form lattice structures of oppositely charged ions
what is the order of the bonding continuum
pure - polar - ionic
what does the difference in electronegativities indicate
ionic character
if there is a large difference between electronegativities is the polarity larger or smaller
larger
how do ions form
when the difference between electronegativities is large, the movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions
are the compounds formed between metals and non-metals always ionic
no, just often
how can you deduce the type of bonding and structure in the compound
through the physical properties of a compound, such as its state at room temperature, melting point and boiling point, solubility and electrical conductivity
do all molecular elements and compounds and monatomic elements condense and freeze at sufficiently low temperatures
yes
what are van der Waals forces
inter molecular forces acting between molecules
what are the types of van der waal’s forces
London dispersion forces and permanent dipole-permanent dipole interactions that include hydrogen bonding
what are London dispersion forces
these are force of attraction that can operate between all atoms and molecules. these forces are much weaker than all other types of bonding.
how are LDFs formed
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 LDFs related to
the number of electrons within an atom or molecule
what is a molecule described as if it has a permanent dipole
polar
what can the spatial arrangement of polar covalent bonds result in
it can result in the molecule being polar
what are permanent dipole-permanent dipole interactions
they are additional electrostatic forces of attraction between polar molecules
are pd-pd interactions stronger than LDFs
yes they are for molecules with similar numbers of electrons
are the bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen highly polar?
yes the 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 are hydrogen bonds
hydrogen bonds are electrostatic forces of attraction between molecules that contain these highly polar bonds. they are stronger than other forms of permanent dipole-permanent dipole interaction but weaker than a covalent bond
how can melting points, boiling points and viscosity be rationalised
in terms of the nature and strength of the intermolecular forces that exist between molecules. by considering the polarity and number of electrons present in molecules, it is possible to make qualitative predictions of the strength of the intermolecular forces
are the melting/boiling points of polar substances higher or lower than the m/b points of non-polar substances with similar numbers of electrons
higher
what are properties of substances that are affected by hydrogen bonding
- boiling points
- melting points
- viscosity
- solubility/miscibility in water
why are the boiling points of ammonia, water and hydrogen fluoride so anomalous
because they have hydrogen bonding
why is ice less dense than water
the hydrogen bonding between the molecules in ice results in an expanded structure that causes the density of ice to be less than that of water at low temperatures
which tend to be soluble in polar solvents such as water and insoluble in non-polar solvents:
A ionic compounds and polar molecular compounds
B non-polar (pure) molecular substances
A
which tend to be soluble in non-polar solvents and insoluble in polar solvents?
A ionic compounds and polar molecular compounds
B non-polar molecular substances
B
what are the key features to be considered when predicting the solubility of a compound?
- presence in molecules of O-H or N-H bonds, which implies hydrogen bonding
- spatial arrangement of polar covalent bonds, which could result in a molecule possessing a permanent dipole
