Covalent bonding

• What is the main focus of the study material?

  The Covalent Model in SL IB Chemistry
• What are the main topics covered in the Covalent Model?

  • Covalent Bonds
  • Lewis Formulas
  • Multiple Bonds
  • Coordinate Bonds
  • Shapes of Molecules
  • Bond Polarity
  • Molecular Polarity
  • Giant Covalent Structures
  • Intermolecular Forces
  • Physical Properties of Covalent Substances
  • Chromatography
• What occurs during covalent bonding?

  Covalent bonding occurs between two non-metals where electrons are shared.

  
• How is a covalent bond formed?

  A covalent bond is formed by the electrostatic attraction between the nuclei of two atoms and their outer shell electrons.

  
• What happens to electrons in covalent bonding?

  No electrons are transferred; they are only shared in covalent bonding.
• What is the significance of overlapping atomic orbitals in covalent bonding?

  Overlapping atomic orbitals form a molecular orbital when a covalent bond is created.
• Why do covalent bonds occur?

  Covalent bonds occur because electrons are more stable when attracted to two nuclei than to just one.

  
• How is a covalent bond represented in diagrams?

  A covalent bond is represented by a short straight line between the two atoms, such as H-H.

  
• How should covalent bonds be viewed in terms of electron pairs?

  Covalent bonds should not be regarded as shared electron pairs in a fixed position; electrons are in constant motion.
• What do non-metals do in covalent bonding?

  Non-metals share pairs of electrons to form different types of covalent bonds.

  
• What is the octet rule?

  The octet rule refers to the tendency of atoms to gain a valence shell with a total of 8 electrons.
• What does it mean to 'expand the octet'?

  'Expanding the octet' means that the central atom can accommodate more than 8 electrons in its outer shell.
• What does it mean if a central atom is 'electron deficient'?

  An 'electron deficient' central atom means it has less than 8 electrons in its outer shell.
• What are the steps for drawing Lewis Formulas?

  1. Count the total number of valence electrons.
  2. Draw the skeletal structure.
  3. Use dots or crosses to represent electron pairs in bonds.
  4. Add more electron pairs to complete octets (except H).
  5. Form double/triple bonds if necessary.
  6. Check total electrons match the valence electrons.

  
• What is a Lewis formula?

  A Lewis formula is a simplified electron shell diagram showing pairs of electrons around atoms.
• How can pairs of electrons be represented in Lewis formulas?

  A pair of electrons can be represented by dots, crosses, a combination of both, or by a line.
• Why is Cl–Cl not a Lewis formula?

  Cl–Cl is not a Lewis formula because it does not show all the electron pairs.
• What is the total number of valence electrons in CH₄?

  8 valence electrons (4 from C and 4 from H).
• What is the total number of valence electrons in NH₃?

  8 valence electrons (5 from N and 3 from H).
• What is the total number of valence electrons in H₂O?

  8 valence electrons (2 from H and 6 from O).
• What is the total number of valence electrons in CO₂?

  16 valence electrons (4 from C and 12 from O).
• What is the total number of valence electrons in HCN?

  10 valence electrons (1 from H, 4 from C, and 5 from N).
• What are the exceptions to the octet rule for elements below atomic number 20?

  • H can achieve stability with 2 electrons.
  • Li achieves stability by losing an electron.
  • Be forms stable compounds with 4 electrons.
  • B and Al can form stable compounds with 6 electrons.
• What are examples of Lewis structures with incomplete octets?

  BeCl₂ and BF₃ are examples of Lewis structures with incomplete octets.
• What is bond energy?

  Bond energy is the energy required to break one mole of a particular covalent bond in the gaseous state.
• What are the units of bond energy?

  Bond energy is measured in kJ/mol.
• How does bond length relate to bond strength?

  The greater the forces of attraction between electrons and nuclei, the shorter the bond length and the stronger the covalent bond.
• Which type of covalent bond is the shortest and strongest?

  Triple bonds are the shortest and strongest covalent bonds.
• What is a coordinate bond?

  A coordinate bond is formed when one atom donates both electrons to an electron-deficient atom.
• What is an example of a coordinate bond?

  An example of a coordinate bond is in the ammonium ion (NH₄⁺).

  
• What are the basic rules of VSEPR theory?

  1. All electron pairs and lone pairs arrange themselves as far apart as possible.
  2. Lone pairs repel more strongly than bonding pairs.
  3. Multiple bonds behave like single bonds.
• What is the bond angle for molecules with two electron domains?

  The bond angle for molecules with two electron domains is 180 degrees.
• What is the shape of molecules with three electron domains?

  Molecules with three electron domains are triangular planar or trigonal planar.
• What happens to bond angles when one of the electron domains is a lone pair?

  The bond angle is slightly less than 120 degrees due to stronger repulsion from lone pairs.

  
• What is an example of a molecule that expands the octet?

  Sulfur dioxide (SO₂) is an example of a molecule that expands the octet.
• What is the bond angle between the bonds when there are three electron domains on the central atom?

  120°
• What shape do molecules with three electron domains adopt?

  Triangular planar or trigonal planar
• Give an example of a molecule with three electron domains that are all bonding pairs.

  BF₃
• What is the bond angle in sulfur dioxide when one electron domain is a lone pair?

  Approximately 118°

  
• Why does the bond angle decrease in molecules with lone pairs?

  Due to stronger repulsion from lone pairs