Chapter 6 Flashcards
electron pair repulsion theory
pairs of electrons around an atom repel eachother so move as far apart as possible to minimise repulsion
solid line=
solid wedge=
dotted wedge=
solid line= bond in the plane of the paper
solid wedge= comes out of the plane of the paper
dotted wedge=goes into the plane of the paper
electronegativity
ability of an atom in a molecule to attract a pair of electrons in a covalent bond to itself
pauling electronegativity values
higher value= higher EN=stronger attraction of bonding electrons to atoms
trend in electronegativity on pauling tavble
trend diagonally to fluorine
electronegativity increases up a group
pure covalent bond
in a non polar bond the electron pair is shared equally between the 2 same bonded atoms with same/similar EN values
polar covalent bond
bonded electron pair is shared unequally between two differing bonded atoms
dipole
separation of opposite charges
symmetrical shape and unsymmetrical shape
symmetrical=dipoles cancel out, non polar
unsymmetrical= dipoles dont cancel out, polar molecule
intermolecular forces
weak interactions between dipoles of different molecules
responsible for physical properties of covalent molecules
all atoms and molecules can exert attractive forces known as
induced dipole-dipole forces/ london forces
london forces
random movement of electrons creates a temporary dipole which induces a neighbouring molecule
non polar molecules only have london forces between
molecules
as molecule size increases, why does melting and boiling point increase?
molecule size increase= induced dipole size= force strength= more energy to overcome= melting and boiling point higher
permanent dipole-dipole interactions
formed between polar molecules(polar bonds and non cancelling shape)
they exert full time stronger forces
simple molecular substances
made up of discrete molecules containing a fixed number of atoms and a consistent molecular formula
when simple molecular substances are solid
they stack up in a lattice molecules= held by weak IM forces and the atoms=strong covalent bonds
properties of simple molecular substances
low melting and boiling points
like dissolves like- depends on dipole strength
not electrically conductive
hydrogen bonds
a special type of permanent dipole-dipole interaction containing a small, strong EN atom with a lone pair and a hydrogen atom attached to an EN atom
why is ice less dense than water
hydrogen bonds hold water apart in an open lattice structure and in ice it is further apart
why does water have a high melting and boiling point
molecule size increase= london force strength=energy need to overcome
why does water have high surface tension
surface molecules experience unbalanced hydrogen bonding forces pulling them in
hydrogen bonding in DNA
DNA’s double helix is held by hydrogen bonds between base pairs
