Bonding: Covalent & Dative Bonding

Question 1

Definition of a Covalent Bond

Answer 1

• A covalent bond is a shared pair of electrons between two atoms

Question 2

Drawing Covalent Bonds

Answer 2

• Two dots represent a lone pair of electrons
• A single line represents a single covalent bond
• A double line represents a double covalent bond
• A triple line represents a triple covalent bond

Question 3

Definition of a Dative (Co-ordinate) Bond

Answer 3

• A dative bond is a covalent bond where the pair of electrons in the bond come from the same atom
- Dative bonds form when one of the atoms in the bond has a lone pair of electrons, and the other doesn’t have any available electrons to share

Question 4

Drawing Dative Bonds

Answer 4

• Dative bonding can be shown with an arrow pointing away from the ‘donor’ atom

Question 5

Covalent Compounds with Fewer Than Eight Outer-Shell Electrons

Answer 5

• When elements with fewer than four outer-shell electrons per atom form compounds they usually lose those electrons to form ions
• Since there are fewer than four electrons available for sharing, there will be fewer than eight outer-shell electrons

Question 6

Covalent Compounds with More Than Eight Outer-Shell Electrons

Answer 6

• If the noble gas rule or octet rule always applied, no atom could have more than eight electrons in its outer shell
• The octet rule always applies for elements in the first two periods of the periodic table (H to Ne).
• However many other elements show can have more than eight electrons in their outer shell when covalently bonded

Question 7

Definition of Macromolecular Crystals & Allotropes

Answer 7

• Substances that have a macromolecular structure are covalently bonded into a giant lattice structure
• Allotropes are different forms of the same element
- Diamond and graphite are allotropes of carbon, and are examples of a macromolecular crystals

Question 8

Structure of Graphite

Answer 8

• Carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with three bonds each
• The fourth outer electron of each carbon atom is delocalised
• The sheets of hexagons are bonded together by weak van der Waals forces

Question 9

Graphite: Melting Point

Answer 9

• Graphite has a very high melting point as you need to break lots of strong covalent bonds, which requires lots of energy

Question 10

Graphite: Conductivity

Answer 10

• Each carbon donates three of its four outer electrons for bonding, the other electron becomes delocalised between the layers
• These delocalised electrons are free to move and carry a current

Question 11

Graphite: Other Properties

Answer 11

• Slippery

• The van der Waals forces between the layers are weak and can be easily broken, so the sheets slide over each other
• Graphite feels slippery and is used as a dry lubricant and in pencils

Question 12

Structure of Diamond

Answer 12

• Each carbon atom is covalently bonded to 4 other carbon atoms
• The atoms arrange themselves in a tetrahedral shape - its crystal lattice structure

Question 13

Diamond: Melting Point

Answer 13

• Diamond has a very high melting point as you need to break lots of strong covalent bonds, which requires lots of energy

Question 14

Diamond: Conductivity

Answer 14

• Diamond does not conduct electricity as all the electrons are involved in bonding
• They have no delocalised electrons