bonding Flashcards
explain the shape of an ammonia molecule
3 bond pairs + 1 lone pair arranged for minimum repulsion; bond angles < 109.5; because bond pair-lone pair repulsion stronger than bond pair-bond pair
explain why boiling point increases down group 7
number of electrons increases down the group; so more energy to break stronger london forces between molecules
explain why lattice energy of CaCO3 is less exothermic than MgCO3
calcium has larger ionic radius and greater shielding; so less attraction between ions
describe the effect of impurities on a substance’s melting temperature
melting temp becomes lower; melts over a range of temperatures
explain why sigma bonds are stronger than pi bonds
sigma: orbitals overlap directly between nuclei; pi: orbitals overlap sideways so further away from nuclei
when can an alkene do E-Z isomerism
when both carbons in a double bond have two different groups attached
what is the difference between E-Z and cis-trans isomerism
cis-trans is same as E-Z but judged using a group present on both carbons
pure silicon forms a giant covalent lattice; explain why it doesn’t conduct electricity even though it has electrons
its outer electrons are used in bonding so they are not free to move
explain why giant covalent lattices have high melting points
high energy needed to break its strong covalent bonds
explain why ionic compounds have high melting points
high energy needed to break its strong ionic bonds
explain why solutions of ions are able to conduct electricity
ions are free to move
suggest why solutions of CaCl2 and BaCl2 of equal concentration have different electrical conductivity
they have different sized cations
what causes london forces to be stronger
more electrons
what is the strongest intermolecular force
hydrogen bonding
what is needed for a hydrogen bond
N-H, O-H or F-H bond on one molecule; lone pair on the other molecule
what is ionic bonding
strong electrostatic attraction between opposite charged ions
how does electrolysis of sodium chloride solution show the presence of ions
chlorine is evolved at the anode, showing there were negative chloride ions present
both Na and NaCl can conduct electricity; compare the conditions needed and the methods of each for conductivity
Na: conducts when solid, delocalised electrons as charge carriers; NaCl: conducts when molten or aqueous, ions as charge carriers
describe the structure of a metal
lattice of positive ions in a sea of delocalised electrons
what is metallic bonding
strong electrostatic attraction between positive ions and delocalised electrons
explain why the melting point of Mg is higher than Na (give 3 reasons)
Mg 2+ has higher charge than Na +; and smaller ionic radius; and contributes more to the sea of delocalised electrons; so more energy to break stronger metallic bonding
explain how metals conduct electricity
delocalised electrons flow when a voltage is applied
explain why a lattice of Mg 2+ and O 2- is stronger than one of Mg + and O -
both ions have higher charge; Mg 2+ is smaller and has less shielding than Mg +
suggest why the melting point of MgO is higher than MgCl2
O 2- ions have higher charge than Cl - ions (and same shielding); so higher energy to break stronger ionic bonding in MgO
explain the shape of a water molecule
2 lone pairs + 2 bond pairs arranged for minimum repulsion; 104.5 degree bond angles; because lone pairs repel more than bond pairs
explain why hydrogen bonds have a ‘bond angle’ of 180 degrees
two electron pairs around H atom; arranged for min repulsion so 180 degrees
describe the formation of london forces
temporary asymmetry in electron density; this creates a dipole that induces more dipoles on other molecules
what is a covalent bond
strong electrostatic attraction between two nuclei and a shared bonding pair of electrons
what is electronegativity
ability of an atom to attract a bonding pair of electrons in a covalent bond
