Dr L : Ionic and covalent compounds

Question 1

When do ionic bonds occur?

Answer 1

Ionic bonds occur between positively charged and negatively charged ions which are held together by strong electrostatic forces of attraction.

Question 2

What is a giant ionic lattice crystal?

Answer 2

Oppositely charged ions held in a regular 3D lattice by electrostatic attraction.

Question 3

What does the arrangement of ions in a crystal lattice depend on?

Answer 3

the relative size of the molecules

Question 4

Describe how ionic bonding happens in group 1-3 metals

Answer 4

• metals lose all outer electrons to non-metals, leaving noble gas structure (full outer shell)
• to form 1+, 2+ or 3+ ions

Question 5

Describe how ionic bonding happens in group 5-7 non-metals

Answer 5

• non metals gain electrons from metals to form noble gas structure
• to form 3-, 2- or 1- ions

Question 6

Which elements do not form ions?

Answer 6

(Be), B, C and Si

• no 4+ ions as too much energy is needed to remove 4 electrons
• no 4- ions as there is too much repulsion between the 4 added electrons

Question 7

What does a giant ionic lattice consist of?

Answer 7

• billions of ions (depending on the size of the crystal)
• ions held together by electrostatic forces of attraction between oppositely charged ions
• a 1:1 ratio of ions to give electrical neutrality

Question 8

What are the properties of ionic compounds?

Answer 8

• ionic crystals do not conduct electricity because the ions are in a fixed position and cannot move
• however ionic melts and solutions do conduct electricity because the lattice is broken down and the ions are free to move
• high melting/boiling points because the strong electrostatic forces of attraction between oppositely charged ions require lots of energy to break
• ionic crystals dissolve in polar solvents, the polar water molecules break down the ionic lattice and surround each ion forming a solution - aluminium oxide is the exception

Question 9

What are molecular ions?

Answer 9

Groups of covalently bonded atoms with a charge, e.g. sulfates, nitrates, hydroxides, ammonium

Question 10

What are the charges of…?
- ammonium
- hydroxide
- nitrate
- carbonate
- sulfate

Answer 10

• NH4+
• OH-
• NO3-
• CO3 2-
• SO4 2-

Question 11

What is a covalent bond?

Answer 11

A covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 12

What is meant by lone pairs of electrons?

Answer 12

Lone pairs of electrons are pairs of electrons which are not used for bonding. A lone pair gives a concentrated region of negative charge around the atom.

Question 13

What is meant by the term ionic bonding?

Answer 13

Ionic bonding is the electrostatic attraction between oppositely charged ions.

Question 14

How does ionic bonding hold particles in MgF2 together?

Answer 14

• Mg forms positive Mg2+ ion
• each F forms negative F- ion
• These are held together because of the strong electrostatic forces of attraction between the oppositely charged ions.

Question 15

What are the half equations for the reaction between magnesium and fluorine?

Answer 15

Mg -> Mg2+ + 2e-
F2 + 2e- -> 2F-

Question 16

Explain why magnesium fluoride has different electrical conductivities when solid and when dissolved in water.

Answer 16

• Ionic compounds do not conduct whn solid as the ions are in a fixed position so can’t move.
• They do conduct when dissolved in water as the lattice becomes broken and the ions become free to move.

Question 17

What is a dative bond?

Answer 17

A shared pair of electrons which has been provided by only one of the bonding atoms.

Question 18

What is meant by bond enthalpy?

Answer 18

Bond enthalpy is the amount of energy required to break a bond.