structure and bonding

Question 1

describe how covalent bonds are formed

Answer 1

covalent bonds are the result of two positive nuclei being held together by their common attraction for the shared pair of electrons

Question 2

state what is meant by the term polar covalent bonds

Answer 2

polar covalent bonds are formed when the atoms in a bond have different electronegativity values

Question 3

describe what happens to the electrons in a polar covalent bond

Answer 3

the atom with a larger electronegativity value attracts the bonding electrons closer to it, this means that it has a delta negative charge and the other atom has a delta positive charge

Question 4

state what is meant by the term pure covalent

Answer 4

pure covalent bonds are formed when the atoms in the bond have the same electronegativity value (ie H2)

Question 5

describe the bonding continuum

Answer 5

the bonding continuum shows the bonds by increasing ionic character
it goes from pure covalent bonds < polar covalent bond < ionic bond

Question 6

describe how the states of compounds at room temperature can help identify the type of bonding

Answer 6

-covalent networks are solid
-covalent molecular are gas or liquids
-ionic substances are solids

Question 7

describe how the melting points of compounds can help identify the type of bonding

Answer 7

covalent molecular have low melting points, covalent networks and ionic substances have high melting points

Question 8

describe the solubility of different compounds

Answer 8

in general, solubility decreases as molecules increase in size. polar covalent compounds and ionic compounds tend to be soluble in water and other polar solvents, non-polar compounds are soluble in non-polar solvents

Question 9

describe the electrical conductivity of different compounds

Answer 9

covalent molecular and covalent networks do not conduct electricity, except graphite. ionic bonds can conduct when molten or in a solution

Question 10

state what is meant by the term intermolecular force

Answer 10

intermolecular forces act between molecules, these are known as van der waals forces

Question 11

name the 3 different types of intermolecular force

Answer 11

london dispersion force (LDF), permanent dipole-permanent dipole interactions (PD-PD I’s), hydrogen bonding

Question 12

explain fully how london dispersion forces arise

Answer 12

LDF’s are formed by the electrostatic attraction between temporary dipoles and induced dipoles which are caused by the movement of electrons

Question 13

describe where london dispersion forces are found

Answer 13

LDFs can operate between all atoms and molecules

Question 14

describe the strength of london dispersion forces

Answer 14

LDFs are the weakest intermolecular force, LDFs get stronger when there are more electrons. as the strength of LDFs increase, the melting/boiling point increases

Question 15

explain when a molecule can be described as being polar

Answer 15

molecules are polar when they have a permanent dipole- one end of the molecule is positive, the other negative, caused by the atoms in the molecule having different electronegativities

Question 16

explain when a molecule can be described as being non-polar

Answer 16

molecules are non-polar when the shape of the molecule is symmetrical

Question 17

describe a pd-pd interaction

Answer 17

pd-pd interactions is the attraction between oppositely charged ends of polar molecules

Question 18

describe the strength of pd-pd interactions

Answer 18

pd-pd interactions are stronger than LDFs. pd-pd interactions are in addition to LDFs

Question 19

describe a hydrogen bond

Answer 19

hydrogen bonds are formed between one molecule which contains hydrogen and another molecule which contains either nitrogen, oxygen or fluorine

Question 20

describe the strength of hydrogen bonds

Answer 20

hydrogen bonds are the strongest intermolecular force

Question 21

explain how intermolecular forces of attraction affect a molecules physical properties

Answer 21

the stronger the intermolecular force, the higher the melting and boiling points. the stronger intermolecular force also increases viscosity

Question 22

explain why ammonia and water have high melting points

Answer 22

they have hydrogen bonds between their molecules which increases melting point

Question 23

explain fully how to predict the solubility of a compound

Answer 23

like dissolves like, so polar compounds will dissolve in polar solvents and non-polar compounds will dissolve in non polar solvents