higher chemistry- unit 1C

covalent bond

result of two positive nuclei being held together by their attraction for a shared pair of electrons

ionic bonding

electrostatic attraction between the positive and negative ions

formed when elements with large difference in electronegativity bond together usually metal and nonmetal

ionic formulae

shape of ionic

written giving simplest ratio of each type of ion in substance ionic compounds form lattice structures of oppositely charged ions

types of bonds on bonding continuum

pure covalent and ionic considered opposite ends with polar covalent lying between two extremes

pure covalent bond ( non-polar covalent bonds )

covalent bonds that form between atoms with same elctronegativity

polar covalent bonds

formed between atoms with different electronegativities

have atoms which are slightly positive and slightly negative leading to permanent dipoles

what does larger difference in electronegativity show

more polar bond will be and greater ionic character

if difference is large how does it affect ion formation

movement of bonding electrons from the element of lower electronegativity to element of higher electronegativity is complete resulting in formation of ions

how to determine or deduce type of bonding and structure in compound

physical properties like state at room temp melting boiling point solubility electrical conducitvity

why is a molecule described as polar

If it has a permanent dipole

one end of molecule of slightly positive and other is slightly negative

other way to which results if molecule is polar or non-polar

spatial arrangement of polar covalent bonds

how do molecular elements compounds and monatomic elements condense and freeze at sufficiently low temperatures

some attractive forces must exist between molecules or discrete atoms

types of intermolecular forces ( Van der waals forces )

london dispersion forces

Permanent dipole to permanent dipole interactions

hydorgen bonds

london dispersion forces

forces 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

result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules

relationship between strength of LDF and number of electrons within atom or molecule

as number of electrons increases LDF increases

Permanent dipole-permanent dipole interactions

additional electrostatic forces of attraction between polar molecules ( stronger than LDF with similar electron number)

hydrogen bond bonded to an atom

strongly electronegative element such as fluorine oxygen nitrogen are highly polar

electrostatic forces of attraction between molecules that contain these highly polar bonds

hydrogen bond strength

stronger than other forms of pd-pd interaction but weaker than covalent bond

how to predict of strength of intermolecular forces

polarity and number of electrons present in molecule

LDF weakest form of intermolecular force

pd slightly stronger

hydrogen stronger again

melting and boiling point and compare of polar and non-polar

depends on strength of force or bond that has to be broken

mp and bp of polar substances are higher than mp or bp of non-polar substances with similar number of electrons

properties of substances affected by hydrogen bonding

boiling point

melting point

viscosity

solubility

miscibility in water

compounds with anomalous boiling point and why

hydrogen fluroride ( HF)

water

ammonia (NH3)

due to presence of hydrogen bonding

hydorgen bonds in nature and desnity of ice

hold proteins and DNA in correct shape

cause ice to float on water

when water chnages to ice it becomes less dense than water at low temp as molecules produce an open expanded structure due to presence of hydorgen bond

what are ionic compounds and polar compounds souble in and not in

polar solvents such as water and insoluble in non-polar solvents

what are non-polar substances soluble in and not

non-polar solvents and insoluble in polar solvents

how to predict solubility of compound key features to be considered are-

presence of molecules of o-h or n-h bonds which implies hydorgen bond

spatial arrangement of polar covalent bonds which results in molecule possessing permanent dipole

viscous liquids

strong intermolecular forces between molecules like substances with hydrogen bonding will be more viscous than substances with no hydorgen bonding