AQA A Level Chemistry复习笔记1.4.3 Covalent Bonding

Covalent Bonding

  • Covalent bonding occurs between two non-metals
  • A covalent bond involves the electrostatic attraction between nuclei of two atoms and the bonding electrons of their outer shells
  • No electrons are transferred but only shared in this type of bonding

1.3-Chemical-Bonding-Defining-Covalent-Bonds

The positive nucleus of each atom has an attraction for the bonding electrons shared in the covalent bond

 

  • Non-metals are able to share pairs of electrons to form different types of covalent bonds
  • Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas
    • This makes each atom more stable

     

 

Covalent Bonds & Shared Electrons Table

1.3-Chemical-Bonding-Table_8

Dot & cross diagrams

  • Dot and cross diagrams are used to represent covalent bonding
  • They show just the outer shell of the atoms involved
  • To differentiate between the two atoms involved, dots for electrons of one atom and crosses for electrons of the other atom are used
  • Electrons are shown in pairs on dot-and-cross diagrams

Single covalent bonding 

Hydrogen, H2

 

1.3-Chemical-Bonding-Single-Covalent-Bonding-Hydrogen

Covalent bonding in hydrogen

 

 

Chlorine, Cl2

1.3-Chemical-Bonding-Single-Covalent-Bonding-Chlorine

Covalent bonding in chlorine

 

 

Hydrogen Chloride, HCl

1.3-Chemical-Bonding-Single-Covalent-Bonding-HCl

Covalent bonding in hydrogen chloride

 

 

Ammonia, NH3

1.3-Chemical-Bonding-Single-Covalent-Bonding-Ammonia

Covalent bonding in ammonia

 

 

Methane, CH4

1.3-Chemical-Bonding-Single-Covalent-Bonding-Methane

Covalent bonding in methane

 

 

Ethane, C2H6

1.3-Chemical-Bonding-Single-Covalent-Bonding-Ethane

Covalent bonding in ethane

 

Double covalent bonding

Oxygen, O2

1.3-Chemical-Bonding-Double-Covalent-Bonding-Oxygen

Covalent bonding in oxygen

 

 

Carbon dioxide, CO2

1.3-Chemical-Bonding-Double-Covalent-Bonding-CO2

Covalent bonding in carbon dioxide

 

Ethene, C2H4

1.3-Chemical-Bonding-Double-Covalent-Bonding-Ethene

Covalent bonding in ethene

 

Triple covalent bonding

Nitrogen, N2

1.3-Chemical-Bonding-Triple-Covalent-Bonding

Covalent bonding in nitrogen

 

  • In some instances, the central atom of a covalently bonded molecule can accommodate more or less than 8 electrons in its outer shell
  • Being able to accommodate more than 8 electrons in the outer shell is known as ‘expanding the octet rule’
  • Accommodating less than 8 electrons in the outer shell means than the central atom is ‘electron deficient’
  • Some examples of this occurring can be seen with period 3 elements

 

1.4.3-Sulfur-dioxide-SO2-%E2%80%93-dot-and-cross-diagram

Sulfur dioxide, SO2 – dot and cross diagram

 

1.3-Chemical-Bonding-Expanding-the-Octet-Rule-PCl5

Phosphorus pentachloride, PCl5 – dot and cross diagram

 

1.3-Chemical-Bonding-Expanding-the-Octet-Rule-SF6

Sulfur hexafluoride, SF6 – dot and cross diagram

Exam Tip

Covalent bonding takes place between nonmetal atoms. Remember to use the periodic table to decide how many electrons are in the outer shell of a nonmetal atom.

 

转载自savemyexams

 

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