Topic 2 - Bonding and Structure Flashcards
what is ionic bonding?
the strong electrostatic attraction between oppositely charged ions
what is covalent bonding?
the strong electrostatic attraction between two nuclei and the shared pair of electrons between them
what is metallic bonding?
the strong electrostatic attraction between the lattice of metal cations and the sea of delocalised electrons
what is a dative covalent bond?
when the shared pair of electrons come from the same atom
what is the shape/angle of a molecule with 3 bonding pairs and 0 lone pairs?
trigonal planar, 120`
what is the shape/angle of a molecule with 2 bonding pairs and 1 lone pair?
bent/v-shape, 118
what is the shape/angle of a molecule with 4 bonding pairs and 0 lone pairs?
tetrahedral, 109.5
what is the shape/angle of a molecule with 2 bonding pairs and 2 lone pairs?
bent, 104.5
what is the shape/angle of a molecule with 5 bonding pairs and 0 lone pairs?
trigonal bipyramidal, 120 and 90
what is the shape/angle of a molecule with 6 bonding pairs and 0 lone pairs?
octahedral, 90
what is the shape/angle of a molecule with 2 bonding pairs and 0 lone pairs?
linear, 180
compare the sizes of anions, cations and atoms of the same element
the negative ion is bigger than the atom - more electrons for the attraction to be distributed, weaker pull
the positive ion is smaller - stronger attraction because less electrons, greater pull
what are the physical properties of ionic compounds?
- high melting points
- non conductor of electricity when solid
- conductor of electricity when molten/aqueous
- brittle
why do ionic compounds have high melting points?
the giant lattice has very strong electrostatic forces between oppositely charged ions
why do ionic compounds not conduct electricity as a solid?
ions are fixed in a lattice, and cannot move to carry charge
why do ionic compounds only conduct electricity when molten/aqueous?
ions are free to move and carry charge
why are ionic compounds brittle?
when ionic compounds are hit (e.g. hammer) it brings ions of the same charge next to each other, and the repulsive forces cause it to shatter
why does electronegativity decrease down a group?
a shell is added, shielding the outermost electrons from the nucleus, making it harder for the nucleus to attract electrons
why do giant atomic structures like diamond and graphite have high melting points?
there are lots of strong covalent bonds that take a lot of energy to break
what determines if a molecule is polar?
presence of polar bonds (electronegativity difference) and asymmetry
what are London forces?
induced dipole-dipole interactions, they are present in all molecular substances apart from ionic.
how are London forces caused?
they are caused by the random/constant movement of electrons. this creates temporary dipoles in neighbouring molecules.
how does electron number affect the size of London forces?
the more electrons there are, the higher chance that they will form temporary dipoles. this makes the London forces stronger.
how does the shape of the molecule affect the size of London forces?
long straight alkanes have a large surface area of contact between molecules for London forces to form, compared to branched alkanes.
where are permanent dipole-dipole forces present?
they occur between polar molecules due to the permanent imbalance of charge
what is hydrogen bonding?
when hydrogen is bonded to an atom more electronegative to it
what three atoms are more electronegative than hydrogen?
nitrogen, oxygen and fluorine
how do ionic substances dissolve in water?
the bonds in the ionic lattice are broken, and new bonds are formed between the metal ions and the water molecules
what is the requirement for a solute to dissolve in a solvent?
the energy required to break the solute/solvent bonds has to be equal to the energy given out to make new bonds between them
why are larger alcohols less soluble in water?
the hydroxyl group is what is able to form hydrogen bonds with water. however, once the hydrocarbon chain increases, the hydroxyl group becomes less significant.
what are the three factors affecting the strength of metallic bonding?
- number of protons - the more protons, the stronger the bond
- number of delocalised electrons - the more electrons the stronger the bond
- size of ion
- smaller ion, the stronger the bond
why do metals have high melting points?
the electrostatic attraction between positive ions and delocalised electrons require a lot of energy to break
why are metal malleable?
the planes of ions in the lattice can easily slide over each other
what type of structure is NaCl?
giant ionic lattice
what type of structure is diamond?
giant covalent lattice
what type of structure is graphite?
giant covalent lattice
what type of structure is magnesium?
giant metallic lattice
why can diamond not conduct electricity?
there are already 4 electrons per carbon atoms, which means they are localised and cannot move.
why can graphite conduct electricity well?
there are delocalised electrons between layers that can carry charge (not from one layer to another)
