bonding notes Flashcards
Metallic Structure and Bonding
giant metallic lattice
strong electrostatic attraction between positive metal ions and delocalised electrons
The bonding in Magnesium is stronger than in Sodium because:
Mg has a greater charge of 2+
Mg has twice as many electrons in the sea of delocalised electrons
Mg ions are smaller, greater charge density
therefore, attraction between Mg2+ ions and delocalised electrons is stronger
properties of metals:
conductivity:
electrical and thermal conductors delocalised electrons to transfer current
strength:
strong electrostatic attraction between positive metal ions and sea of delocalised electrons
malleable and ductile:
hammered into shape
pulled into wires
rows of metal ions can slide past one another
melting and boiling points:
strength of metallic bonds;
stronger they are;
higher mp and bp
Covalent Structure and Bonding
macromolecular and simple
molecular
A covalent bond is a shared pair of electrons between two atoms
macromolecular structures:
silicon
carbon
silicon oxide
Diamond:
Each C has 4 covalent bonds
tetrahedral shape
very high mp
very hard
non conductor (no delocalised electrons)
graphite:
layers with 3 covalent bonds to each C atom
each C has a delocalised electron
layers held together by weak intermolecular forces
soft layers can slide over one another
conductor has delocalised electrons
mp high
forces and properties of simple molecular structures;
IMFs act between molecules
melting causes breaking of IMFs
IMFs weaker than covalent bonds
low MP
Ionic structure and bonding:
Giant ionic lattice
strong electrostatic attractions between oppositely charged ions
Physical and structural properties of ionic compounds:
high mp and bp
electrical conductivity - aqueous or molten
brittle and shatter easily
ammonium:
NH4+
hydroxide
OH-
nitrate
NO3-
nitrite
NO2-
hydrogencarbonate
HCO3-
Chlorate(I)
CIO-
Chlorate(v)
CIO3-
carbonate
CO32-
sulfate
SO42-
sulfite
SO32-
dichromate
Cr2O72-
phosphate
PO43-
Coordinate bonds
A coordinate bond is a shared pair of electrons which have both come from the same atom
Define electronegativity
the ability of an atom to attract electron density from a covalent bond
The factors which determine how electronegative an element are:
nuclear charge
the atomic radius
the shielding
why is fluorine the most electronegative?
as you go UP groups - electronegativity INCREASES because radius and amount of shielding DECREASES
as you move ACROSS a period - electronegativity INCREASES beaches the nuclear charge INCREASES and the radius DECREASES
what are the three types of intermolecular forces?
induced dipole dipole (van der waals forces)
permanent dipole dipole
hydrogen bonding
when does hydrogen bonding occur?
occurs between H and lone pair on either: N, O, F
strongest IMF
how does hydrogen boding arise?
very large difference in electronegativity between Oxygen (NOF) and H
creates a dipole on the O-H bond
lone pair on oxygen atom in one molecule strongly attracts a partially positive H on a different molecule
when do permanent dipole dipole forces occur?
between polar molecules
generally weaker than hydrogen bonding
how do permanent dipole dipole forces arise?
difference in electronegativity leads to bond polarity
dipoles don’t cancel out, therefore the molecule has an overall permanent dipole
there is an attraction between s+ on one molecule and s- on another
when do induced dipole dipole forces (VDWs) occur?
occurs between all molecules but most important for non polar molecules
generally the weakest force but can be stronger than hydrogen bonding and permanent dipole dipole if molecule is large enough = lots of electrons
how do induced dipole dipole occur?
Random movement of electrons in one molecule leads to…
Uneven distribution of electrons, creating a…
Temporary dipole in one molecule…
Induces dipole in a neighbouring molecule
Dipoles attract
importance of hydrogen bonding
ice: less dense than water because the hydrogen bonds in ice hold the molecules further apart
proteins: they’re held in their complex 3D shapes by hydrogen bonds
the shape of a protein is vital for its function
DNA: carries all genetic information of living things
the two strands in the double helix are held together by hydrogen bonds
strong enough to hold together and weak enough to allow strands to separate for semi conservative replication
physical properties in period 3 elements
mp and bp (na to mg to al)
increases
strong attraction between cation and delocalised electrons
charge on ion increases
size decreases
more delocalised electrons
physical trends in period 3 elements :
silicon
macromolecular
to melt Si many strong covalent bonds must be broken
which requires a large amount of energy
therefore Si has the highest MP
physical trends in period 3 elements :
P, S, Cl
simple molecular
P4 S8 Cl2
covalent bonding between atoms
VDWs forces between molecules
weak forces
S8 slightly highest MP and BP = greater electrons
S8>P4>Cl2
physical trends in period 3 elements :
Ar
monoatomic
no bonding
weakest vdws between atoms
least amount of e-
smallest
