Bonding and structure

Question 1

define the term ionic bonding

Answer 1

the electrostatic force of attraction between oppositely charged ions (formed by electron transfer)

Question 2

why are positive ions smaller compared to their ions?

Answer 2

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

Question 3

define the term covalent bond

Answer 3

a shared pair of electrons

Question 4

how is coordinate bonding formed?

Answer 4

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

Question 5

define metallic bonding

Answer 5

the electrostatic force of attraction between the positive metal ions and the delocalised electrons

Question 6

what are the main factors affecting the strength of metallic bonding?

Answer 6

1. number of protons : the more protons the stronger the bond
2. number of delocalised electrons per atom : more delocalised electrons = stronger bond
3. size of ion = the smaller the ion the stronger the bond

Question 7

e.g question why does Mg have stronger metallic bonding than Na?

Answer 7

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.

Question 8

what are the different structures that covalent bonding has?
give examples of each

Answer 8

simple molecular or macromolecular

small molecules = CO2 IODINE, ICE , H20
macromolecular = diamons, graphite , silicon dioxide , silicon

Question 9

bond angle and bonding pairs of linear shape

Answer 9

bond angle = 180 degrees
bonding pairs = 2

Question 10

bond angles + bonding pairs of trigonal planar

Answer 10

bond angles = 120 degrees
bonding pairs = 3

Question 11

bond angles + bonding pairs in tetrahedral

Answer 11

bond angle = 109.5
bonding pairs = 4

Question 12

bond angles + bonding pairs in trigonal bipyramidal

Answer 12

bond angle = 90 and 120
bonding pairs = 5

Question 13

bond angles + bonding pairs in octahedral

Answer 13

bond angle = 90
bonding pairs - 6

Question 14

bond angle + bonding pairs in bent

Answer 14

bond angle = 104.5
bonding pairs = 2
lone pairs = 2

Question 15

bond angle + bonding pairs in trigonal pyramidal

Answer 15

bond angle = 107
bonding pairs = 3
lone pairs = 1

Question 16

bond angle + bonding pairs in square planar

Answer 16

bond angle = 90
bonding pairs = 4
lone pairs = 2

Question 17

define electronegativity

Answer 17

is the power of an atom to attract electrons in a covalent bond

Question 18

what are the factors affecting electronegativity?

Answer 18

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

Question 19

how is a permanent dipole formed?

Answer 19

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.

Question 20

how are VDWF formed?

Answer 20

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.

Question 21

what is the main factor affecting van der waals?

Answer 21

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

Question 22

VDWF and the trend in increasing bp of alkanes

Answer 22

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.

Question 23

permanent dipole-dipole forces

Answer 23

*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

Question 24

hydrogen bonding

Answer 24

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