chem bonding– the covalent model
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define covalent bonding
the electrostatic FOA between the nucleus of each of the 2 bonded atoms and their shared pair of e-
what is another name for dative bond
coordinate bond
what are dative bonds
the covalent bond established by the donation of an e- pair from one atom to another
to form a dative bond, 1. the donor atom must contain ______________________ 2. and the acceptor atom must have a _______________
• lone pair of e- • vacant orbital
what are the exceptions to the Lewis structure?
BCl3 -> only 6 valence e- BeCl2 -> only 4 valence e-
what type of orbital overlap do sigma bonds have? (letters)
s-s, p-p, s-p
pi bonds are the _______ overlap of ______ orbitals
side on, p
draw a sigma bond
-
draw a pi bond
-
is the pi or sigma bond stronger?
sigma
why is the sigma bond stronger
it has head on overlap of orbitals
does the covalent bond strength decrease or increase down the group?
decrease
why does the strength of covalent bonds down the group decrease?
• the atomic radius incr • effectiveness of orbital overlap decr • thus strength decr
the stronger the bond, the [shorter/longer] the bond length
shorter
across the period, electronegativity [incr/decr] down the group, electronegativity [incr/decr]
increases decreases
why can some central atoms expand their octet?
these elements can utilise their energetically accessible vacant 3d orbitals
what is the bond angle of a molecule that is trigonal planar, bent
less than 120º
what is the bond angle of a tetrahedral molecule
109.5º
the bond angle of a tetrahedral trigonal pyramidal molec is [greater/lesser] than a tetrahedral bent molec
greater
if an atom has 5 electron pairs what is its electron domain geometry?
trigonal bipyramidal
how many bond pairs on the central atom would lead to a see-saw shape?
4
draw the orbitals involved in the hybridisation of a carbon atom in methane
-
why does diamond have very high m.p.?
• each C atom is covalently bonded to 4 other C atoms in a tetrahedral shape • has strong and extensive C-C covalent bonds throughout giant covalent lattice • reqs large amts of energy to break
can diamond conduct electricity and why?
no, no mobile ions/e-