4. Bonding

Question 1

cations

Answer 1

Positive ions formed by metals losing valence electrons.

Question 2

anions

Answer 2

Negative ions formed by non-metals gaining electrons.

Question 3

state the factor that determines the number of electrons lost/gained

Answer 3

the electron configuration of the atom

Question 4

ionic bond

Answer 4

electrostatic attraction between oppositely charged ions

Question 5

state of most ionic compounds at room temperature

(with lattice structures)

Answer 5

solids

Question 6

structure of ionic compounds

Answer 6

Giant Ionic Lattice - a repeating 3D structure of negative and posetive ions bonded together by strong electrostatic attraction

Question 7

melting/boiling point of ionic compounds

Answer 7

high - due to the strong electrostatic attractions between the oppositly charged ions a large amount of energy is needed to overcome these forces

Question 8

conductivity of ionic compounds

Answer 8

in solid form - does not conduct electricity because the oppositely charged ions are not able to move freely between the positive and negative electrodes and are unable to carry and electrical charge
in a liquid/melted - does conduct electricity because the oppositely charged ions are able to move freely between the positive and negative electrodes and carry an electrical charge

can conduct when in liquid form

Question 9

state the factors that determines the charge of an ion

Answer 9

the number of electrons the atom needs to lose/gain to achieve a full outer shell

Question 10

solubility of ionic compounds

Answer 10

many are soluble in water - the energy given out when ions become hydrated (hydration energy) provides the energy to overcome the forces holding the ions together in the lattice (lattice enthalpy)

Question 11

polyatomic ions

Answer 11

ions containing more than one element

Question 12

give the names of the polymatic ions:
NH4+, OH-, NO3-, HCO3-, CO3-2, SO4-2, PO4-3

Answer 12

• ammonium NH4+
• hydroxide OH-
• nitrate NO3- (from nitric acid, HNO3)
• hydrogencarbonate HCO3-
• carbonate CO3-2 (from carbonic acid, H2CO3)
• sulfate SO4-2 (from sulfuric acid, H2SO4)
• phosphate PO4-3 (from phosphoric acid H3PO4)

Question 13

covalent bond

Answer 13

the electrostatic attraction between a shared pair of electrons and the posetively charged nuclei

Question 14

single, double and triple covalent bond

Answer 14

involve one, two and three shared pairs of electrons respectively

Question 15

state the relationship between bond length, bond strength and the number of shared electrons

do they increase/decrease

Answer 15

bond length decreases and bond strength increases as the number of shared electrons increases

Question 16

bond polarity

Answer 16

results from the difference in electronegativities of the bonded atoms

Question 17

trends in electronegativity values

electronegativity values for each element can be found in section 8 of the IB data booklet

Answer 17

generally, the values increase across a period and decrease down a group

Question 18

state the factors that determine whether a molecule is polar or not

Answer 18

• relative electronegativities of the atoms in the molecules (bond polarity)
• its shape

Question 19

how is bond polarity shown

Answer 19

either with partial charges, dipoles or vectors

Question 20

Lewis (electron dot) structures

dot and cross diagrams

Answer 20

show all the valence electrons in covalently bonded species

Question 21

“octet rule”

Answer 21

the tendancy of atoms to gain a valence shell with a total of 8 electrons

Question 22

exceptions to “octet rule”

Answer 22

some atoms, like Be and B, might form stable compounds with incomplete octets of electrons

Question 23

resonance structures

Answer 23

occur when there is more than one possible position for a double bond in a molecule

Question 24

how is the charge of an ion related to its position in the periodic table

Answer 24

• element (metals) on the left side of the periodic table form positive ions whilst elements on the righ side (non metals) form negative ions
• the group number indicates the number of valence electrons and how many it needs to lose/gain to have a full outer shell

Question 25

ion

Answer 25

an atom that has lost/gained an electron from its outer shell