Chemical bonding

Question 1

Ionic bonding

Answer 1

the electrostatic force between cations and anions in an ionic crystal lattice

Question 2

Covalent bonds

Answer 2

formed when the outer electrons of two atoms are shared

Question 3

How are atoms between molecules kept together ?

Answer 3

by strong covalent bonds

Question 4

Van der Waals’ forces

Answer 4

weak forces between molecules

-> intermolecular forces

Question 5

Types of Van der Waals’ forces

Answer 5

• dipole
• permanent dipole-permanent dipole ( pd-pd forces )
  -hydrogen bonding

Question 6

London dispersion forces ( dipole )

Answer 6

instantaneous dipole-induced dipole ( id-id ) forces

Question 7

Hydrogen bonding

Answer 7

stronger form of pd-pd force

Question 8

How are ions formed

Answer 8

by the gain or loss of electrons in atoms

Question 9

Positive ions ( Cations )

Answer 9

when an atom loses one or more electrons

-> mostly metals

Question 10

Negative ions ( Anions )

Answer 10

when an atom gains one or more electrons

-> mostly non-metals

Question 11

Lattice

Answer 11

a regularly repeating arrangement of atoms, molecules or ions in 3-D throughout the whole crystal structure

Question 12

Ionic bond

Answer 12

the electrostatic attraction between oppositely charged ions ( cations & anions )

Question 13

Electrovalent bond

Answer 13

Ionic bond

Question 14

Dot-and-cross diagram

Answer 14

a diagram showing the arrangement of the outer-shell electrons in an ionic/ covalent element/compound

Question 15

Dot-and-cross diagram structure

Answer 15

• outer shells only
• the charge of the ion is spread only, by using square brackets
• the charge on each ion, shown on the right-hand top corner

Question 16

Covalent bonding

Answer 16

when two non-metals share one or more pairs of electrons

Question 17

Single covalent bond / bond pair

Answer 17

the electrostatic attraction between the nuclei of two atoms and a shared pair of electrons

represented by a single line between atoms

ex : Cl-Cl

Question 18

Lone pair

Answer 18

pairs of electrons in the outer shell of an atom that are not involved in bonding

Question 19

Double covalent bonding

Answer 19

two shared pairs of electrons bonding 2 atoms together

represented by a double line between atoms

ex : O=O

Question 20

Dative covalent bonding /
Co-ordinate bonding

Answer 20

the sharing of electrons between two atoms where both the electrons in the bond come from the same atom

Question 21

Needs for dative bonding

Answer 21

• one atom has a lone pair of electrons
• a second atom to have an unfilled orbital to accept the lone pair
  -> electron deficient

Question 22

Electron deficient

Answer 22

an atom/molecule that has less than its usual share of electrons

Question 23

Bond energy

Answer 23

the energy required to break one mole of a particular covalent bond in gaseous state

Question 24

Bond length

Answer 24

the distance between the nuclei of two covalently bonded atoms

Question 25

Shape & bond angle of a covalently bonded molecule depends on :

Answer 25

- number of pairs of electrons around each atom - whether these pairs are lone pairs or bonded pairs

Question 26

VSEPR

Answer 26

Valence Shell Electron Pair Repulsion Theory

Question 27

Shapes of molecules

Answer 27

- linear ( v-shape ) - trigonal planar - tetrahedral - trigonal bipyramid - octahedral

Question 28

Linear

Answer 28

- 2 electron pairs - 180°

Question 29

Trigonal planar

Answer 29

- 3 electron pairs 120°

Question 30

Tetrahedral

Answer 30

- 4 electron pairs - 109.5

Question 31

Trigonal bipyramid

Answer 31

- 5 electron pairs - 90°, 120°

Question 32

Octahedral

Answer 32

- 6 electron pairs - 90°

Question 33

Molecular orbital

Answer 33

combined orbital formed when the atomic orbitals in the formation of a covalent bond overlap - contains 2 electrons

Question 34

Hybridisation

Answer 34

the mixing of atomic orbitals

Question 35

Sigma bonds ( σ )

Answer 35

formed from end-on overlap of atomic orbitals

Question 36

Pi bonds ( π )

Answer 36

formed from sideways overlap of atomic orbitals

Question 37

Metallic bonding

Answer 37

the electrostatic attraction between positive ions and delocalised electrons

Question 38

Delocalised electrons ( mobile electrons )

Answer 38

electrons that are not associated with any particular atoms

Question 39

Delocalised electrons in metals

Answer 39

move throughout the metallic structure between the metal ions when a voltage is applied

Question 40

Strength of metallic bonding increases with :

Answer 40

- increasing positive charge on the ions in the metal lattice - decreasing size of metal ions in the lattice - increasing number of mobile electrons per atom

Question 41

Properties of metals :

Answer 41

- high MP & BP - conduct electricity - conduct heat

Question 42

Metals as an electricity conductor

Answer 42

when a voltage is applied to a metal, electric current flows through it because the mobile electrons are free to move

Question 43

Metals as a heat conductor

Answer 43

- mainly due to the vibrations passed from one metal ion to the next - partly due to the movement of delocalised electrons

Question 44

Electronegativity

Answer 44

the power of a particular atom that is covalently bonded to another atom to attract the bonding pair of electrons towards itself

Question 45

Pattern of electronegativity from Group 1-17

Answer 45

- increases across a period - increases down a group

Question 46

Most electronegative element

Answer 46

Fluorine

Question 47

Order of the most electronegative elements

Answer 47

Br < Cl < N < O < F

Question 48

Factors influencing electronegativity :

Answer 48

- atomic radius - nuclear charge - shielding

Question 49

Scale of electronegativity values

Answer 49

Pauling electronegativity -> Np

Question 50

electronegative difference is high ( ≥ 2.0 )

Answer 50

ionic

Question 51

electronegative difference is low ( < 1.0 )

Answer 51

covalent

Question 52

Non-polar molecules

Answer 52

- electronegativity values of the two atoms forming a covalent bond are the same - equally shared pair of electrons

Question 53

Polar molecule ( dipole )

Answer 53

- different electronegative values between two atoms forming a covalent bond - electron distribution is asymmetric

Question 54

In molecules containing more than 2 atoms, we have to take into account :

Answer 54

- the polarity of each bond - the arrangement of each bonds in the molecule

Question 55

Polar bonds

Answer 55

the electron pair in the atom is drawn towards the atom having the larger electronegativity, making one end of the molecule slightly positive compared to the other

Question 56

Induced

Answer 56

one molecule brings about an attractive or repulsive effect on the other

Question 57

id-id forces

Answer 57

- Instantaneous dipole - induced dipole forces - weakest intermolecular attractive force - dipoles not permanent - London dispersion forces

Question 58

id-id forces increase with :

Answer 58

- increasing number of electrons & protons in the molecule - increasing the number of contact points between the molecules

Question 59

pd-pd forces

Answer 59

- attractive intermolecular forces which result from permanent dipoles in a molecule

Question 60

For hydrogen bonding to happen, the molecules must have :

Answer 60

- a H atom atom bonded to a highly electronegative atom - another highly electronegative atom with a lone pair of electrons

Question 61

Hydrogen bond

Answer 61

- strongest type of intermolecular force - weaker than covalent bonds - strong type of pd-pd force

Question 62

The average number of hydrogen bonds formed per molecules depends on :

Answer 62

- number of hydrogen atoms attached to F,O or N - the number of lone pairs present on the F,O or N

Question 63

Properties of water :

Answer 63

- high enthalpy change of vaporisation & BP - Surface tension & viscosity