bonding Flashcards
(39 cards)
structure and bonding of metals
metallic bond is the electroststatic force of attraction between metal cations and sea of delocalised electrons.
each metal atom contributes its loosely held valence electron to form the sea of delocalised electrons.
mp and bp of metals
high mp and bp as large amounts of energy required to overcome strong metallic bonds between cations and sea of delocalised electrons in the lattice structure during a change in physical state
electrical conductivity of metals
presence of mobile electrons to act as charge carriers. when a potential difference is applied, the delocalised electrons flow through the lattice towards the positive potential
malleability of metals
non-directional character of metallic bonding and the mobility of the sea of delocalised electrons allow metal ions in the structure to slide past each other, readily accommodating any distortion in the lattice without fracturing. the metal lattice does not break as the sea of delocalised electrons prevents repulsion between cations
properties of alloys
harder and strong than pure metals as the addition of other cations causes a less regular metal structure, making it more difficulty for metallic ions to slide past each other
increased electrical resistance and lower conductivity, as lattice is less regular which affects the mobility of electrons
factors affecting strength of metallic bond
greater no. of electrons contributed per atom to form the sea of delocalised eletcrons, greater metallic bond strength
smaller cationic radius, greater metallic bond strength
structure and bonding of ionic compounds
electrostatic forces of attraction between oppositely charged ions in an ionic compound.
formation by complete transfer of valence electrons from a atom to another
in solid state, oppositely charged ions held in fixed positions by strong ionic bonds in an orderly manner to form a regular 3d crystal lattice structure
factors affecting ionic bond strength (lattice energy)
energy released when 1 mole of ionic solid is formed from its constituent gaseous ions, magnitude of LE represents energy required to overcome giant ionic lattice.
greater charge product, larger magnitude of lattice energy, greater ionic bond strength
shorter interionic distance, large magnitude of lattice energy, greater ionic bond strength
if determinants contradict, effect of charge product outweighs effect of interionic distance.
hardness of ionic solids
ions are held in specific positions throughout crystal lattice by strong ionic bonds
moving ions out of position requires overcoming strong forces of attraction, thus ionic solids resist denting
when sheer stress applied, layers of ions will slide past each other, resulting in repulsion between like charged ions, causing ionic crystal to break
electrical conductivity of ionic solids
in solid state cannot conduct electricity as ions are held in fixed positions by strong ionic bonds, absence of mobile charge carriers
molten and aqueous state can conduct electricity as ionic crystal lattice is broken down and ions acts as mobile charge carriers to conduct electricity
solubility of ionic solids
when ionic solid is placed in water, each ion on crystal’s surface attracts oppositely charged poles of polar water molecules, forming extensive ion-dipole interactions, which releases sufficient energy to overcome the ionic bonds and break down crystal lattice, hence solid dissolves
mp and bp of ionic solids
large amounts of energy required to strong ionic bonds between oppositely charged ions in the lattice structure during a change in physical state
covalent bonds
electrostatic force of attraction of positively charged nuclei of each bonding atom for the shared pair of electrons
sigma bond
formed by head-on overlap of 2 atomic orbitals, where the shared electron density is concentrated along the inter-nuclei axis.
can only be one sigma bond between any two atoms as it is not possible for another head-on overlap of the atomic orbitals between the same pair of atoms
pi bond
formed by side-way overlap of two p atomic orbitals, where shared electron density is concentrated above and below the inter-nuclei axis of bonding atoms
strength of sigma bond vs pi bond
strength of covalent bond increases with more effective orbital overlap, and thus sigma bond is strong than pi bond as head on overlap is more effective than side-way overlap
pi bond is only formed after sigma bond is formed (double bond has 1 sigma and 1 pi, while triple bond as 1 sigma and 2 pi)
coordinate bond
where both electrons in the covalent bond comes from only one of the atoms
formed when a filled valence orbital of an atom overlaps with a vacant valence orbital of another atom, where an atom donates a lone pair of electrons to another atom which has an energetically accessible orbital (empty and low-lying) to accommodate the electrons
factors affecting strength of covalent bonds
bond order : higher bond order, greater electron density shared between bonding atoms, greater attraction between bonding nuclei and shared pair of electrons, strong covalent bond
effectiveness of orbital overlap : smaller atom, more effective orbital overlap, stronger covalent bond
simple molecular structure
strong covalent bond between atoms but simple discrete molecule held by comparatively weak intermolecular forces
low melting and boiling point as small amounts of energy required to overcome weak intermolecular forces of attraction
soluble in non-polar organic solvents
cannot conduct electricity due to absence of mobile charge carriers
giant molecular lattice structure (diamond)
sp3 hybridised carbon atom forms strong covalent bond with 4 carbon atoms in 3 dimensional tetrahedral arrangement throughout the lattice
high mp and bp as large amounts of energy required to break strong covalent bonds throughout the lattice
cannot conduct electricity due to absence of mobile charge carriers
hard as atoms are held rigidly by strong covalent bond throughout covalent lattice
insoluble in all solvents
giant molecular structure (graphite)
sp2 hybridised carbon atom forms strong covalent bonds with 3 other carbon atoms in a 2 dimensional layer of hexagonal carbon rings, with weak intermolecular forces between graphene layers
can conduct electricity due to highly mobile pi electrons located above and below graphene layers
high mp and bp as c-c covalent bonds are stronger than the c-c bond in diamond, has a higher mp and bp than diamond
slippery and lubricating purposes as weak intermolecular forces of attraction instead of strong covalent bonds are formed between graphene layers, enabling layers to slide over one another easily
why does ClO2 exist but not FO2
dot and cross diagram shows a total of 11 electrons around the central atom of Cl, but this is not possible is F was the central atom. F is a period 2 element and has a total of 4 orbitals in n=2 electron shells, and can only accommodate up to 8 electron in its valence shell. even though F can form coordinate bonds, where F does not achieve an pocket arrangement, it is not energetically favourable to donate 2 electron pairs to O as F is more electronegative than O
factors affecting polarisation of ionic bond
charge to size ratio of cation : higher charge to size ratio, greater ability of cation to distort electron cloud of anion, higher polarising power
size of anion : larger electron cloud size, electron cloud more distant from nucleus, easier attraction and distortion by cation
greater polarisation, greater covalent character
why is AlCl3 a covalent and not ionic
Al3+ ion has high polarising power due to its high charge to size ratio. electron clouds of anions from period 3 and above are more easily distorted due to the larger size. greater shared electron density in AlCL3, greater covalent character
