Molecular Structure Flashcards
Covalent bond
Electrostatic attraction between 2 nuclei and one or more shared pairs of electrons between them
Covalent bonding
Sharing of 1 or more pairs of electrons
Describe a sigma orbital
2 s/p orbitals overlap along x axis
Can rotate one end
Bond doesnt break
Describe a pi orbital
2 p orbitals overlap along y/z axis
Cant rotate one end
Bond breaks
Which the of orbital are the first shared pair of electrons found in
Sigma
In which orbital are electrons more tightly bound
Sigma
Compare the relative strengths and lengths of single double and triple covalent bonds
Single, low strength, long
Double, mid strength, mid length
Triple, high strength, short
Name 6 unconventional dot and cross diagram formations
Less than full shell
Compound ions
Dative
Free radical electrons
More than 8 electrons in a shell (not shell 2)
Mixture of diagrams
Buzz words for simple molecule shape questions
No. Bonding pairs
No. Lone pairs
No. Density points
Shape
Minimises repulsion
Angle, squeezed?
Weighted lone pairs
4 sigma bonds, 0 lps
Tetrahedral
109.5*
3 sigma bonds, 1 lps
Triangular based pyramid
Lp repels more than bps
107*
Ammonia
2 sigma bonds, 2 lps
V shape
Los repel more than bps
104.5*
Water
2 sigma bonds, 0 lps
Linear
180*
3 sigma bonds, 0 lps
Trigonal plane
120*
5 sigma bonds, 0 lps
Trigonal bypyramid
3: 120*
2: 90*
6 sigma bonds, 0 lps
Octahedron (8 faces)
4: 90*
2: 90*
What is the shape of a molecule determined by
Repulsion between electron pairs around central atom
Define electronegativity
Ability of an atom to attract bonding e tronos in a covalent bond
4 most electronegative elements
F
O
Cl
N
Describe how electronegativity can lead to a polar BOND
Electron spends more time near one atom
Warps orbital shape
partial neg/pos charges
Describe how electronegativity can lead to a polar MOLECULE
Polar bonds that don’t cancel each other out
Polarity = vectors
Name 3 intermolecular forces
London forces
Permanent dipoles
Hydrogen bonds
Describe london forces
Temporarily uneven electron distribution
Small dipole
Atom near another induces a dipole
Name 3 factors that vary London force strength
Grip on outer electrons (more grip, less induction)
No. Electrons in molecule (more, more induction)
Molecule shape (more SA contact, more induction, branched < un branched
Describe permanent dipole forces
Electronegative molecules
Oppositely charged ends orient together
Describe hydrogen bonding
One molecules with a lp on N, O or F
One molecule with an H covalently bonded to an N, O or F
Recite NH3 HF H2O hydrogen bonding table
NH3, 1 lp, 3 Hs, 1 HB
HF, 3 lp, 1 H, 1 HB
H2O, 2 lp, 2 H, 2 HB
Name and describe 4 unique properties of water
High surface tension, strong H bond between molecules
High heat capacity, thermal energy stored in H bond vibrations
Liquid denser than solid/solid more volumous than liquid, long H bond length
