S2.2 Covalent

Question 1

what is a covalent bond?

Answer 1

formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei

Question 2

what does the theory of bonding propose?

Answer 2

that molecules are formed by overlapping regions of space allowing atoms to mutually share pairs of electrons

Question 3

what is the linear combination of atomic orbital theory(LCAO)?

Answer 3

regions of space where electrons are found are called orbitals and the bond comes from direct overlap of atomic orbitals

Question 4

what is the octet rule?

Answer 4

the tendency of atoms to gain a valence shell with 8 electrons

Question 5

what is the expanding the octet rule?

Answer 5

being able to accommodate more than 8 electrons in the outer shell and can be done if they use d subshell

Question 6

what is electron deficient?

Answer 6

accommodating less than 8 electrons in the outer shell

Question 7

how do london forces(induced dipole dipole) form?

Answer 7

temporary dipole, electrons are constantly moving, electrons on an adjacent atom are repelled by the negative part of the dipole which results in an attraction

Question 8

what does the strength of London(dispersion) forces depend on?

Answer 8

the number of electrons in the molecule, SA of the molecules

Question 9

how does the no. of electrons affect the forces?

Answer 9

more electrons=greater likelihood of a distortion

Question 10

how does the SA of a molecule affect the London forces?

Answer 10

larger SA=more contact with adjacent molecules

Question 11

how do dipole-dipoles form?

Answer 11

molecules with permanent dipoles are attracted to each other by permanent dipole-dipole bonding

Question 12

how do dipole-induced dipole attractions form?

Answer 12

when the permanent dipole of a polar molecule causes a temporary separation of charge on a non-polar molecule

Question 13

how does hydrogen bonding form?

Answer 13

strongest intermolecular force-type of permanent dipole-permanent dipole bonding

Question 14

what does the term Van der Waals’ forces include?

Answer 14

London dispersion, dipole-induced dipole, dipole-dipole

Question 15

what is a coordinate bond and give an eg.

Answer 15

when one atom uses a lone pair of electrons to form a covalent bond eg with NH3 and a H+ ion to form ammonium

Question 16

in an expanded octet what does the charge signify?

Answer 16

no. of single bonds

Question 17

why does molecular geometry change when there are lone pairs on the central atom?

Answer 17

lone pairs are closer to the central nucleus so closer to bonding pairs, so lone pairs repel bonding pairs more strongly, so they move closer together and the bond angles decrease, 2 lone pairs cause greater repulsion than 1, so bond angle decreases as their numbers increase

Question 18

describe structure of diamond

Answer 18

tetrahedral array, very hard, high m.p. and b.p., cant conduct electricity

Question 19

describe structure of graphite

Answer 19

layered structure, hexagonal rings, delocalised electrons, high mp., can conduct within layers but not through them

Question 20

describe structure of graphene

Answer 20

single layer of graphite, flexible, can conduct

Question 21

describe structure of buckminsterfullerene

Answer 21

gigantic structure, 60 carbon atoms, alternating hexagons and pentagons, weak intermolecular forces, low mp, can’t conduct

Question 22

what is average bond enthalpy?

Answer 22

the strength of the bond

Question 23

how does the size of the + charge on the nucleus effect electronegativity?

Answer 23

across a period, no. of protons increases, so increased + charge increases attraction between nucleus and pair of electrons in covalent bond so elements on right are more electronegative

Question 24

how does the atomic radius effect electronegativity?

Answer 24

smaller atomic radius=closer the bonding electrons are to nucleus, across of a period atomic radius decreases so on right elements more electronegative

Question 25

how does shielding affect electronegativity?

Answer 25

more shielding=more electronegative

Question 26

draw the 2 ways to show a polar bond

Answer 26

S+ and S- and the arrow pointing towards more electronegative atom with a line near the start

Question 27

what is an overall polarity called?

Answer 27

a dipole moment

Question 28

write up induced dipole-dipole; permanent dipole-dipole and hydrogen bonding

Question 29

properties of water because of hydrogen bonding

Answer 29

high m.p. and b.p.

Question 30

why is the solid form is less dense than liquid eg how ice floats on water?

Answer 30

in water, sometimes molecules are closer sometimes further apart so H bonds constantly being formed and broken, as water cools molecules move slower, reaching the freezing point(0), water molecules arrange themselves into ordered structure(ice) which is stabilised by network of H bonds, in ice water molecules further apart than in liquid making ice less dense than liquid water so floats on surface which insulates water below preventing from freezing under

Question 31

properties of simple molecular substances

Answer 31

atoms are covalently bonded to each other, have small molecules w a fixed no. of atoms