Chemical Bonding

Question 1

Define Ionic Bond

Answer 1

• A strong electrostatic attraction between the oppositely charged cations and anions in the giant ionic lattice
• Primarily exist between metal cations and non-metal anions, such as in sodium chloride and magnesium oxide

Question 2

Define Covalent Bond

Answer 2

• A strong electrostatic attraction between the positively charged nuclei of atoms and their shared pair of electrons
• Primarily exist between non-metal atoms, such as in hydrogen, oxygen, nitrogen, chlorine, hydrogen chloride, carbon dioxide, methane and ethene

Question 3

Define Metallic Bond

Answer 3

A strong electrostatic attraction between the cations and the sea of delocalised valence electrons in the giant metallic lattice

Question 4

Define Co-ordinate (dative covalent) bonds

Answer 4

Formed when both the electrons in the covalent bond are provided by only one of the bonded atoms, such as in the formation of the ammonium ion and in the Al2Cl6 molecule

Question 5

How is a σ bond formed?

Answer 5

• Atomic orbitals overlap head-on and the shared pair of electrons occupy the space between the nuclei

Question 6

How is a π bond formed?

Answer 6

π bond is formed when atomic orbitals overlap side-on and the shared pair of electrons occupy the space above and below the nuclear axis

Question 7

Describe Covalent Bonding in terms of orbital overlap

Answer 7

• Covalent bonds involve the overlap of atomic orbitals to form molecular orbitals, and consist of σ and/or π bonds
• s orbitals can only form σ bonds while two p orbitals can form both σ and π bonds
• π bonds are weaker than σ bonds and can only form when the atoms already possess a σ bond
• Single bonds consist of 1 σ bond, double bonds consist of 1 σ bond and 1 π bond and triple bonds consist of 1 σ bond and 2 π bonds

Question 8

What is the Valence Shell Electron Pair Repulsion theory?

Answer 8

Electron pairs in the valence shell of a central atom will arrange themselves in space as far as possible from each other to minimise mutual repulsion

Question 9

Explain the shapes of and bond angles in molecules by using the Valence Shell Electron Pair Repulsion theory

Answer 9

The repulsion between lone pairs is the greatest, followed by that between a lone pair and a bond pair, and lastly that between bond pairs. By determining the number of bond pairs and lone pairs present on the central atom, the Valence Shell Electron Pair Repulsion theory can be used to predict the shapes of and bond angles in molecules analogous to BF3, CO2, CH4, NH3, H2O and SF6.

Question 10

Shape and Bond Angles: BF3

Answer 10

• Trigonal planar shape
• bond angle of 120°
• 3 bond pairs and 0 lone pairs surrounding the central atom

Question 11

Shape and Bond Angles: CO2

Answer 11

• linear shape
• bond angle of 180°
• 2 bond pairs and 0 lone pairs surrounding the central atom

Question 12

Shape and Bond Angles: CH4

Answer 12

• Tetrahedral shape
• bond angle of 109°
• 4 bond pairs and 0 lone pairs surrounding the central atom

Question 13

Shape and Bond Angles: NH3

Answer 13

• Trigonal pyramidal shape
• bond angle of 107°
• 3 bond pairs and 1 lone pair surrounding the central atom

Question 14

Shape and Bond Angles: H2O

Answer 14

• Bent shape
• Bond angle of 105°
• 2 bond pairs and 2 lone pairs surrounding the central atom

Question 15

Shape and Bond Angles: SF6

Answer 15

• Octahedral shape
• Bond angle of 90°
• 6 bond pairs and 0 lone pairs surrounding the central atom

Question 16

What is an electronegativity of an atom?

Answer 16

A measure of its ability to attract the shared pair of electrons in a covalent bond towards itself

Question 17

How to deduce bond polarity using the concept of electronegativity?

Answer 17

• When atoms of similar electronegativity form a covalent bond, the bonding electrons are shared equally between the atoms, resulting in the bond being nonpolar
• When atoms of different electronegativities form a covalent bond, the more electronegative atom attracts the bonding electrons more strongly, forming a dipole, resulting in the bond being polar

Question 18

What is a dipole?

Question 19

Deduce the polarity of a molecule using bond polarity and its molecular shape

Answer 19

1. No polar bonds = nonpolar
2. Polar bonds + dipoles cancel each other out = nonpolar
3. Polar bonds + dipoles do not cancel each other out = the polarity of the molecule is the vector sum of the dipole moments in each covalent bond

Question 20

What are intermolecular forces?

Answer 20

Weak electrostatic forces of attraction between simple covalent molecules resulting from interactions between permanent or induced dipoles

Question 21

What are Polar Molecules?

Answer 21

Polar molecules such as liquid and gaseous CHCl3 have net dipole moments with permanent dipole-permanent dipole interactions between oppositely charged ends of neighbouring molecules

Question 22

How are instantaneous dipole-induced dipole interactions between molecules formed?

Answer 22

In any molecule, including Br2 and the noble gases, an asymmetrical charge distribution at a particular instant could result in temporary dipoles that induce dipoles in neighbouring molecules, resulting in instantaneous dipole-induced dipole interactions between molecules formed.

Question 23

Gas VS Liquid in terms of intermolecular forces of attraction

Answer 23

The molecules of a gas have negligible intermolecular forces of attraction while those of a liquid have some intermolecular forces of attraction

Question 24

What is Hydrogen Bonding?

Answer 24

The process where an electrostatic attraction is formed between a H atom bonded to an N, O or F atom and a lone pair on the N, O or F atom of a neighbouring molecule

It is stronger than other permanent dipole-permanent dipole interactions which in turn are stronger than instantaneous dipole-induced dipole interactions

Question 25

How does pressure affect IMF?

Answer 25

At high pressure, molecules are pushed closer together, forming intermolecular forces of attraction, until the molecules are close enough for the physical state to change from gas to liquid

Question 26

How does temperature affect IMF?

Answer 26

At low temperature, the molecules move more slowly, bringing them closer to each other, resulting in the formation of intermolecular forces and hence liquefaction

Question 27

Importance of intermolecular forces to the liquefaction of gases when subjected to high pressure and/or low temperature

Answer 27

The ease of liquefaction of gases depends on the strength of the intermolecular forces – low temperature is sufficient for most gases, high pressure is used for gases with stronger intermolecular forces and both conditions are required for gases with very weak intermolecular forces

Question 28

Importance of hydrogen bonding to the physical properties of substances

Answer 28

• higher melting and boiling points as more energy is required to overcome the stronger hydrogen bonds than the weaker intermolecular forces
• Hydrogen-bonded substances with larger dipole moments have higher melting and boiling points as more energy is required to overcome the stronger hydrogen bonds between molecules
• Can influence the lattice structure of simple molecular solids

Question 29

Hydrogen Bonding: Ice

Answer 29

Molecules in ice are arranged in a tetrahedral lattice structure with each O atom covalently bonded to 2 H atoms and hydrogen-bonded to 2 H atoms, resulting in less molecules present per unit volume
In contrast, molecules in liquid water have sufficient energy to overcome the hydrogen bonds and slide over one another without any regular arrangement of molecules, resulting in more molecules present per unit volume

Question 30

What is Bond Energy?

Answer 30

The energy required to break one mole of covalent bonds between two atoms in the gaseous state under standard conditions

Question 31

What is Bond Length?

Answer 31

The internuclear distance between the two bonding atoms

Question 32

Compare of the reactivities of covalent bonds in terms of bond energy

Answer 32

Covalent bonds with larger bond energies are less reactive as they require more energy to break during chemical reactions

Question 33

Compare of the reactivities of covalent bonds in terms of bond length

Answer 33

Covalent bonds with shorter bond lengths have a greater degree of orbital overlap and hence a higher bond energy, making them less reactive

Bond length is a more important factor than bond polarity in determining the bond energy and reactivity of the covalent bond

Question 34

Compare of the reactivities of covalent bonds in terms of bond polarity

Answer 34

Polar covalent bonds experience extra attraction between the partial charges, giving them higher bond energies and hence lower reactivities than nonpolar covalent bonds

Question 35

Lattice Structure of an ionic solid

Answer 35

An ionic solid, such as NaCl or MgO, has a giant ionic structure consisting of a lattice of cations and anions held together by ionic bonds

Question 36

Lattice Structure of a simple molecular solid

Answer 36

A simple molecular solid, such as iodine, has a simple molecular structure with intermolecular forces of attraction between molecules

Question 37

Lattice Structure of a giant molecular solid

Answer 37

A giant molecular solid, such as graphite or diamond, has a giant molecular structure with atoms held together by covalent bonds

Question 38

Lattice Structure of a hydrogen-bonded solid

Answer 38

A hydrogen-bonded solid, such as ice, has a simple molecular structure with hydrogen bonds between molecules

Question 39

Lattice Structure of a metallic solid

Answer 39

A metallic solid, such as copper, has a giant metallic structure consisting of a lattice of cations and a sea of delocalised valence electrons held together by metallic bonds

Question 40

How strength of bonds between particles affect physical properties

Answer 40

More thermal energy is required to overcome stronger chemical bonds between particles. Hence, substances with giant structures have higher melting and boiling points than substances with simple structures, and giant covalent substances have higher melting and boiling points than ionic or metallic substances

Question 41

How mobile ions affect the physical properties of a substance?

Answer 41

Mobile charge carriers, in the form of mobile ions or free electrons, are required for a substance to conduct electricity – hence, metals conduct electricity in the solid state, ionic compounds do so only when molten or in aqueous solution, and most covalent substances do not conduct electricity

Question 42

Explain what affects solubility in structure and bonding?

Answer 42

For a substance to be soluble, the energy released during interaction between solute and solvent particles must be enough to overcome the forces between solute particles and between solvent particles