Bonding and structure Flashcards
define the term ionic bonding
the electrostatic force of attraction between oppositely charged ions (formed by electron transfer)
why are positive ions smaller compared to their ions?
this is because it has one less shell of electrons and the ratio of protons to electrons has increased meaning theres a greater net force on the remaining electrons holding them more closely
define the term covalent bond
a shared pair of electrons
how is coordinate bonding formed?
when the shared pair of electrons in a covalent bond comes from only one of the bonding atoms. ALSO KNOWN AS DATIVE COVALENT. Examples include: NH4+,H3O+,NH3BF3
define metallic bonding
the electrostatic force of attraction between the positive metal ions and the delocalised electrons
what are the main factors affecting the strength of metallic bonding?
- number of protons : the more protons the stronger the bond
- number of delocalised electrons per atom : more delocalised electrons = stronger bond
- size of ion = the smaller the ion the stronger the bond
e.g question why does Mg have stronger metallic bonding than Na?
Mg has stronger metallic bonding than Na and hence a higher melting point. The metallic bonding gets stronger because in Mg there are more electrons in the outer shell that are released to the sea of electrons. The Mg ion is also smaller and has one more proton. There is therefore a stronger electrostatic attraction between the positive metal ions and the delocalised electrons and higher energy is needed to break bonds.
what are the different structures that covalent bonding has?
give examples of each
simple molecular or macromolecular
small molecules = CO2 IODINE, ICE , H20
macromolecular = diamons, graphite , silicon dioxide , silicon
bond angle and bonding pairs of linear shape
bond angle = 180 degrees
bonding pairs = 2
bond angles + bonding pairs of trigonal planar
bond angles = 120 degrees
bonding pairs = 3
bond angles + bonding pairs in tetrahedral
bond angle = 109.5
bonding pairs = 4
bond angles + bonding pairs in trigonal bipyramidal
bond angle = 90 and 120
bonding pairs = 5
bond angles + bonding pairs in octahedral
bond angle = 90
bonding pairs - 6
bond angle + bonding pairs in bent
bond angle = 104.5
bonding pairs = 2
lone pairs = 2
bond angle + bonding pairs in trigonal pyramidal
bond angle = 107
bonding pairs = 3
lone pairs = 1
bond angle + bonding pairs in square planar
bond angle = 90
bonding pairs = 4
lone pairs = 2
define electronegativity
is the power of an atom to attract electrons in a covalent bond
what are the factors affecting electronegativity?
Electronegativity increases across a period as the number of protons increases and the atomic radius decreases because the electrons in the same shell are pulled in more. It decreases down a group because the distance between the nucleus and the outer electrons increases and the shielding of inner shell electrons increases
how is a permanent dipole formed?
A polar covalent bond forms when the elements in the bond have different electronegativities . When a bond is a polar covalent bond it has an unequal distribution of electrons in the bond and produces a charge separation, (dipole) δ+ δ- ends.
how are VDWF formed?
These are also called transient, induced dipole-dipole interactions. They occur between all simple covalent molecules and the separate atoms in noble gases. In any molecule the electrons are moving constantly and randomly. As this happens the electron density can fluctuate and parts of the molecule become more or less negative i.e. small temporary or transient
dipoles form. These instantaneous dipoles can cause dipoles to form in neighbouring molecules. These are called
induced dipoles. The induced dipole is always the opposite sign to the original one.
what is the main factor affecting van der waals?
The more electrons there are in the molecule the higher the chance that temporary dipoles will form. This makes the Van der Waals stronger between the molecules and so boiling points will be greater
VDWF and the trend in increasing bp of alkanes
The increasing boiling points of the alkane homologous series can be explained by the increasing
number of electrons in the bigger molecules causing an increase in the size of the Van der Waals
between molecules. The shape of the molecule can also have an effect on the size of the Van der Waals forces. Long chain
alkanes have a larger surface area of contact between molecules for Van der Waals to form than compared to
spherical shaped branched alkanes and so have stronger Van der Waals.
permanent dipole-dipole forces
*Permanent dipole-dipole forces occurs between polar molecules
*It is stronger than Van der Waals and so the compounds have higher boiling points
*Polar molecules have a permanent dipole. (commonly compounds with C-Cl, C-F, C-Br H-Cl, C=O bonds)
*Polar molecules are asymmetrical and have a bond where there is a significant difference in
electronegativity between the atoms
hydrogen bonding
It occurs in compounds that have a hydrogen atom attached to one of the three most electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of
electrons. e.g. a –O-H -N-H F- H bond. There is a large electronegativity difference between the
H and the O,N,F
