Topic 3: Bonding Flashcards
Ionic
Large differences in electronegativity, between metals and non metals. Electrostatic att’n b/w charged ions.
Covalent
Small differences in electronegativity, between non metals. Shared pair of electrons.
Metallic
Between metals. Electrostatic att’n b/w ions and delocalised e-
Ionic Structure
Giant ionic lattice
Ionic Properties
- High melting point … strong att’n between oppositely charged ions means hard to overcome, higher the charge, higher the att’n, higher the melting point
- Electrical conductor when molten/ in sol’n… Ions can dissociate and so are free to move and can carry charge.
Covalent Properties (Diamond and Sillicon)
- High melting point/ hard… lots of strong covalent bonds, hard to overcome.
Covalent Properties (Graphite)
- High melting point (same reason as diamond)
- Slippery… weak v.d.w. between layers so can slide
- Conducts electricity… single delocalised electron can carry charge
Covalent Properties (Iodine)
- Low boiling point… weak v.d.w. forced between molecules, little energy required to overcome.
Metalic Properties
- High melting point… strong att’n between delocalised electrons and cations, greater the charge the more electrons, the stronger the att’n.
- Electrical conductors… delocalised electrons can move throughout structure and carry charge
- Malleable/ ductile… layers of ions can slide also means brittle
Malleable def
The ability of a something to be deformed or shaped without breaking
Ductile
The ability of a something to be stretched or drawn into wire form without breaking
Dative Bonding
A covalent bond in which both electrons come from the same atom (a lone pair).
2 Bonding pairs
Linear, 180°, O=C=O
3 Bonding pairs
Trigonal Planar, 120 °, looks like flat triangle with 3 bonds, BF3
4 Bonding pairs
Tetrahedral, 109.5 ° 3D shape you know it, CH4
5 Bonding pairs
Trigonal Bipyramid, 120° and 90° straight up, straight down, straight left, right up to the back, right down to the front, PCl5
6 Bonding pairs
Octahedral, 90°, straight up, straight down, sides up, sides down, SF6
3 Bonding pairs, 1 Lone pair
Trigonal Pyramid, 107°, tetrahedral without the top atom, NH3
2 Bonding pairs, 2 Lone pairs
Angular, 104.5°, V shapes, H20
Intermolecular Forces
The attractive and repulsive forces that arise between the molecules of a substance.
Van der Waals forces
- Weakest IMF
- Exist in all molecules or atoms
- The electron charge cloud constantly moving (electron density is uneven)
- The electron charge cloud can be more on one side of the atom or molecule than the other
- This causes a temporary dipole to arise
- This induce a dipole on neighbouring molecules
- When this happens, the δ+ end of the dipole in one molecule and the δ- end of the dipole in a neighbouring molecule are attracted towards each other
- Because the electron clouds are moving constantly, the dipoles are only temporary
Strength of V.d.w difference in different molecules
The larger the molecule/atom, the more electrons so greater electrostatic att’n, stronger v.d.w forces.
Saturated/ unsaturated fats and v.d.w
Saturated fats have stronger v.d.w as they have straight chains so can fit together and form more v.d.w. Opposite for unsaturated as have a kink in chain.
Dipole- dipole forces
- Occurs in permanently polar molecules
- Uneven distribution of electron cloud
- This means there is a delta positive and delta negative region to the molecule
- Interacts with other molecules, electrostatic att’n to opposite delta charge
- The greater the polarity of a bond or molecule, the stronger the permanent dipole-dipole interactions.
Hydrogen Bonding
- Strongest IMF
- O, N or F bonded to H
- Lone pairs
- Attraction between H and lone pair on the delta negative region of other molecule (O,N or F)
Electronegativity
The power of an atom to attract electron density in a covalent bond.
Electronegativity trend
Down the group - decreases - increased shielding
Across the period - increases - nuclear charge increases - atomic radius decreases
Polar Bond
Bond between atoms of elements with different electronegativities so that the electrons are asymmetrically distributed between the atoms.
IMFs in water
More hydrogen bonding occurs causing a regular lattice arrangement of water molecules. Expands. Molecules are further apart than in liquid. Lower density so it floats.
Include on h bonding diagram
Lone pairs
Delta charges
Dotted line
