1.3 Bonding Flashcards
(25 cards)
Define metallic bonding:
- the attraction between positive metal ions and delocalised outer shell electrons in a lattice
Define ionic bonding:
- the electrostatic force of attraction between oppositely charged ions in a lattice (metal/non-metal)
What is a non-octet molecule?
- when the central atom does not have a noble gas electron arrangement
What is a dative/co-ordinate bond?
- a covalent bond in which both electrons of the shared pair come from the same atom
Describe electron repulsion theory:
- when pairs of electrons in the outer shell arrange themselves to be as far apart as possible
- to minimise repulsion
- lp-lp > lp-bp > bp-bp
What are the 2 bond angles in a trigonal bipyramidal shaped molecule?
- 90’ and 120’
What is the bond angle in a V-shaped molecule with 1 lone pair?
- 117.5’
(120-2.5)
What is the bond angle in a V-shaped molecule with 2 lone pairs?
- 104.5’
(109.5-2x2.5)
What is the bond angle in a pyramidal molecule?
- 107’
Describe and explain the trend in electronegativity across a period:
- increases across a period
- because proton number increases but the outer electrons are in the same shell (same distance from nucleus)
- greater attraction on the outer electron
Describe and explain the trend in electronegativity down a group:
- decreases down a group
- because the number of shells/shielding increases
- less nuclear attraction on the outer electron
What are the 5 most electronegative elements?
- F, O, N, Cl, Br
What is a non-polar bond?
- there is no/very small difference in electronegativity between atoms
- they have the same/similar attraction on the shared pair of electrons
»> the electrons in the bond are evenly distributed
Example: C-C or C-H
What is a polar bond?
- when there is a difference in electronegativity between atoms
- this causes a PERMANENT DIPOLE
- electrons spend more time with the more electronegative atom»_space;> unevenly distributed
Examples: C=O, O-H, H-N
Explain how Van der Waals forces occur in molecules:
- movement of electrons unbalances the charge distribution within a molecule
- creates an instantaneous dipole
- instantaneous dipole is constantly forming and disappearing
- this induces a dipole in neighbouring molecules
- results in weak forces of attraction between molecules
What are permanent dipole-dipole forces?
- forces that occur between molecules with a permanent dipole (polar)
- the delta + end of one molecule is attracted to the delta - end of a neighbouring molecule
Compare Van der Waals and permanent dipole-dipole forces:
- Van der Waals occur in all molecules, permanent d/d only occur in polar molecules
- permanent d/d are usually stronger than Van der Waals, except if the v/d/w molecule is very large
Describe hydrogen bonding:
- a H bonded to either a F, O or N
- occurs between a delta + atom and a lone pair on the F/O/N on the neighbouring molecule
*strongest intermolecular force
What are 2 properties of H-bond substances?
- higher boiling points than expected
- tend to dissolve in water
Why do substances with H-bonding tend to dissolve in water?
- they form hydrogen bonds with H2O
Why does ice have a lower density than water?
- when H2O freezes, hydrogen bonds hold the H2O molecules apart in an open tetrahedral lattice
Solubility of polar/non-polar substances:
- ionic and polar substances dissolve in polar solvents (water)
- non-polar substances dissolve in non-polar solvents (hexane)
What are the properties of metals?
- high melting points
- conduct electricity (delocalised electrons)
- strong (strong metallic bonds)
- malleable and ductile
Why are metals malleable and ductile?
- layers of ions in the giant ionic lattice can slide over each other into new positions without disrupting the metallic bonds
