Bonding - Topic 2.2 Chemistry Flashcards
what are intermolecular forces
weak forces between molecules
give 3 types of intermolecular forces
- london forces
- dipole-dipole bonds
- hydrogen bonding
what are london forces
cause all atoms and molecules to be attracted to each other
how are london forces created
electrons in charge clouds are always moving, so the electrons are likely to be more to one side than the other, creating a temporary dipole. This dipole can induce another temporary dipole in the opposite direction. The two dipoles are then attracted to each other
how is a simple molecular structure formed from iodine molecules
the iodine atoms are held together in pairs by strong covalent bonds. But, the molecules are also held together in a molecular lattice by weak london forces
in which 2 conditions do stronger london forces occur
- larger electron clouds
- molecules with greater surface areas, as bigger exposed electron clouds
why does a longer carbon chain have stronger london forces
because there’s more molecular surface contact and more electrons to interact
why do branched-chain alkanes have fewer london forces
because they’re branched, they can’t pack closely together, so their molecular surface contact is smaller
what are dipole-dipole bonds
weak electrostatic forces of attraction between molecules in a polar molecule
when does hydrogen bonding occur
when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
what happens to hydrogens bonding pair in a hydrogen bond
fluorine, nitrogen or oxygen are very electronegative, so they draw the bonding electrons away from the hydrogen atom
why does the hydrogen atoms form weak bonds with the lone pairs of electrons of N, F or O atoms of molecules
Hydrogen atoms form weak bonds with the lone pairs of N, F, or O atoms because these elements are highly electronegative, creating a partial positive charge on hydrogen that attracts the lone pair’s partial negative charge.
what do organic molecules that form hydrogen bonds often contain
- OH group
- NH group
why are substances that form hydrogen bonds soluble in water
because they can form hydrogen bonds with the water molecules, allowing them to mix and dissolve
why does ice float on water
ice is a simple molecular structure, as the water molecules are arranged so that there is the maximum number of hydrogen bonds. As the ice melts, hydrogen bonds are broken, breaking down the lattice, such that the ice is less dense than water
