bonding (physical) Flashcards
what is ionic bonding
strong electrostatic force between oppositely charged ions
give an example of an ionically bonded substance
sodium chloride (NaCl)
how high are ionically bonded substances’ boiling and melting points? why?
very high because it takes a lot of energy to break electrostatic forces between oppositely charged ions
do ionic compounds conduct electricity? why?
yes when molten/dissolved in a solution because they are free to move around and hold a charge. they do not conduct electricity when solid
what is simple molecular covalent bonding?
strong covalent bonds between atoms, weak van der waals forces between molecules
are there any lone electrons in simple covalent bonding
no
can simple covalent bonds conduct electricity? why?
no because all of the electrons are used in bonding and arent free to move
do simple molecular covalent substances have high or low boiling and melting points? why?
low because there are weak van de Waals forces that dont need much energy to overcome
describe macromolecular covalent bonding
lattice of many atoms held together by strong covalent bonds
do substances with macromolecular covalent bonds have high or low melting and boiling points? why?
high because it takes a lot of energy to overcome lots of covalent bonds
do substances with macromolecular covalent bonds conduct electricity? why?
most of them dont as electrons are all used in bonding
graphite does as there is a delocalised electron from each carbon free to carry charge
describe the structure of diamond
tetrahedral 3D structure of carbon atoms, each bonded to 4 other carbon atoms
describe the structure of graphite
each carbon atom is bonded to 3 other carbons so it is in layers.
there are weak van de waals forces in between layers so that they can easily slide over eachother.
one electron from each carbon is delocalised so can conduct electricity
describe metallic bonding
lattice of positive metal ions attracted to a sea of delocalised electrons
layers can also slide over eachother meaning they are malleable
do metallic compounds have low or high melting and boiling points? why?
high because there are strong forces of attraction between metal ions and negatively charged sea of delocalised electrons
do metallic compounds conduct electricity? why?
yes because there are delocalised electrons free to carry charge
how does the strength of metallic bonds change across the periodic table? why?
strength increases - higher melting and boiling points
higher charge on metal ions
more delocalised electrons per ion
stronger force of attraction between them
define electronegativity
the ability of an atom to attract the pair of electrons (the electron density) in a covalent bond
what affects electronegativity? (3)
nuclear charge
atomic radius
electon shielding
what is the most electronegative element?
fluorine (4.0 on paulings scale) largest nuclear charge for its electron shielding and a small atomic radius
how do you get a non-polar bond?
both bonding elements have the same electronegativities
when do you get a polar bond?
when both elements have different electronegativities
what is the strongest type of intermolecular force
hydrogen bonding
what is the weakest type of intermolecular force?
van der Waals forces
describe Van der Waals forces
temporary dipoles are created by random movement of electrons -> induces dipole in neighbouring molecule
are van der Waals forces stronger in smaller or larger molecules
larger because there are more electrons
describe permanent dipole-dipole attraction
some molecules with polar bonds have permanent dipoles (forces of attraction between those dipoles and those of neighbouring molecules)
what conditions are needed for hydrogen bonding to occur
O-H, N-H or F-H bond
lone pair of electrons on O,N,F because they are highly electronegative so H nucleus is left exposed
strong forces of attraction between H nucleus and lone pair of electrons on O, N,F
why is ice less dense than liquid water
in liquid water, hydrogen bonds constantly break and reform as molecules move around
in ice, the hydrogen bonds hold the molecules in fixed positions which makes them slightly further apart than liquid water
what is a dative/co-ordinate covalent bond? when is it formed?
formed when an electron deficient atom/ion accepts a lone pair of electrons from an atom with a lone pair of electrons not used in bonding
what does the shapes of molecules depend on?
number of electrons in the valence shell of the central atom
number of these electrons that are bonded or lone pairs
what does the electron pair repulsion theory state?
the electron pairs will take up positions as far away as possible to minimise the repulsive forces between them
which experience the most repulsion?
lone pair-lone pair
bonded pair-bonded pair
lone pair-bonded pair
lone pair - lone pair (strongest)
lone pair - bonded pair
bonded pair - bonded pair (weakest)
what is the shape, and angle in a shape with 2 bonded pairs and 0 lone pairs
linear , 180°
what is the shape and angle of a shape with 3 bonded pairs and 0 lone pairs
trigonal planar , 120°
what is the shape and angle of a shape with 4 bonded pairs and 0 lone pairs
tetrahedral , 109.5°
what is the shape and angle of a shape with 5 bonded pairs and 0 lone pairs
trigonal bipyramid
90° and 120°
what is the shape and angle of a shape with 6 bonded pairs and 0 lone pairs
octahedral
90°
what is the shape and angle of a shape with 3 bonded pairs and 1 lone pair
trigonal pyramidal, 107°
what is the shape and angle of a shape with 2 bonded pairs and 2 lone pairs
non linear, 104.5°
how are ionic compounds soluble in polar substances such as water
the polar solution surrounds the ions and can overcome the electrostatic forces of attraction
how do lone pairs effect repulsion
decrease the angle by 2.5°
