Shapes of molecules

• What theory predicts the shape and bond angles of molecules?

  Valence shell electron pair repulsion theory (VSEPR)
• Why do electrons repel each other in a molecule?

  Because they are negatively charged
• What forces a molecule to adopt a specific shape?

  Minimization of repulsive forces
• What are valence shell electrons?

  Electrons in the outer shell
• How do lone pair electrons compare to bonded pairs in terms of repulsion?

  Lone pairs repel more than bonded pairs
• How is repulsion treated between multiple and single bonds?

  It is treated the same as single bonds
• What is the repulsion order of electron pairs?

  Lone pair-lone pair > lone pair-bond pair > bond pair-bond pair
• Why do lone pairs have a more concentrated electron charge cloud?

  Because they are not shared with other atoms
• What shapes and bond angles can molecules adopt?

  • Linear: 180°
  • Trigonal planar: 120°
  • Bent: <120°
  • Tetrahedral: 109.5°
  • Trigonal pyramidal: 107°
  • Bent: 104.5°
  • Trigonal bipyramidal: 120° (equatorial), 90° (axial)
  • Seesaw: <120° (equatorial), <90° (axial)
  • T-shaped: <90°
  • Linear: 180°
  • Octahedral: 90°
  • Square pyramidal: <90°
  • Square planar: 90°

  
• What is the shape of phosphorus(V) chloride?

  Trigonal bipyramidal

  
• How many valence electrons does phosphorus have?

  Five valence electrons
• What shape does N(CH₃)₃ have?

  Triangular pyramid
• How many valence electrons does nitrogen have?

  Five valence electrons
• What is the shape of CCl₄?

  Tetrahedral

  
• What is electronegativity?

  Power of an atom to attract electrons
• What happens to electron distribution in a covalent bond with different electronegativities?

  It becomes unsymmetrical
• What scale is used to assign electronegativity values?

  Pauling scale
• Which atom is the most electronegative?

  Fluorine

  
• What is the relationship between nuclear charge and electronegativity?

  Increased nuclear charge increases electronegativity

  
• How does atomic radius affect electronegativity?

  Increased atomic radius decreases electronegativity

  
• What effect does shielding have on outer electrons?

  It reduces the attraction to the nucleus
• Why does sodium have higher electronegativity than caesium?

  It has fewer shells and less shielding
• What are the trends in electronegativity down a group?

  • Decreases down a group
  • Nuclear charge increases
  • Increased shielding from filled electron shells
  • Larger atomic radii result in decreased attraction

  
• What are the trends in electronegativity across a period?

  • Increases across a period
  • Nuclear charge increases with protons
  • Shielding remains constant
  • Stronger attraction for bonding electrons

  
• What is the general trend of electronegativity in the periodic table?

  Increases towards the top right

  
• What are intramolecular forces?

  Forces within a molecule, usually covalent bonds

  
• What are intermolecular forces?

  Forces between different molecules
• What are the types of intermolecular forces?

  1. Induced dipole-dipole (London dispersion forces)
  2. Permanent dipole-dipole forces
  3. Hydrogen bonding

  
• How do intramolecular forces compare to intermolecular forces?

  Intramolecular forces are stronger than intermolecular forces
• What is the strength of a hydrogen bond compared to a covalent bond?

  About one tenth the strength
• What defines a polar bond?

  Atoms have different electronegativities
• What happens in a nonpolar covalent bond?

  Atoms have the same electronegativity
• What are the two main types of forces in molecules?

  Intramolecular and intermolecular forces
• What are intermolecular forces?

  Forces between molecules
• What are the three types of intermolecular forces?

  • Induced dipole-dipole forces (London dispersion forces)
  • Permanent dipole-dipole forces
  • Hydrogen bonding

  
• What are induced dipole-dipole forces also known as?

  Van der Waals or London dispersion forces
• What are permanent dipole-dipole forces?

  Attractive forces between neighboring polar molecules

  
• What is hydrogen bonding?

  A special type of permanent dipole-dipole force

  
• How do intramolecular forces compare to intermolecular forces?

  Intramolecular forces are stronger
• How strong is a hydrogen bond compared to a covalent bond?

  About one tenth the strength