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Bonding & Molecular Structure. Physical Science K Warne. Atoms and molecules (simple and giant ). H. H. H. O. O. O. -. -. -. +. +. +. H. H. H. Intermolecular forces. Two different types of bonds occur in water. Intramolecular
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Bonding & Molecular Structure Physical Science K Warne
H H H O O O - - - + + + H H H Intermolecular forces • Two different types of bonds occur in water. • Intramolecular • Between hydrogen atoms and oxygen atomsinside the molecules Covalent bonds • Intermolecular • Betweentwo different water molecules Hydrogen bonds
H - O + H Bond Polarity in Water The oxygen atom has greater electronegativity so it is surrounded by greater electron density than the hydrogen atoms. + H - O H + - + The water molecule is a DIPOLE - it has two oppositely charged “poles”.
H H H O O O - - - + + + H H H Hydrogen Bonding Example: Water • The oppositely charged poles on the water molecules attract each other. • This electrostatic attraction constitutes Hydrogen bonding. • It is the strongest form of intermolecular attraction. • Hydrogen bonding exists only between molecules in which hydrogen is bonded to a very electronegative atom (H-O-X, H-NX2 or H-F). • Result in abnormally high boiling points.
Molecular solids Strong covalent bonds Iodine - I2 • PROPERTIES • Low melting points • Brittle • Soluble in non-polar solvents • Non - conducting Weaker intermolecular bonds Covalently bonded molecules held together by weaker intermolecular bonding.
. . : X . . . . . : X . . . IMF vs Mp & Bp Mp & Bp increases with SIZE and molecule MASS
Density • Density = mass/volume (g.cm-3) 1cm x 1cm x 1cm = 1cm3 Low density – gases Few particles per cm3 High density – solids Many particles per cm3
Effect of Temp • Temperature is a measure of average kinetic energy. • As temperature rises more particles have high energy. Maxwell-Boltzman Curve Average Ek Increases
Effect of Temp Maxwell-Boltzman Curve • Temperature is a measure of average kinetic energy. • As temperature rises – particles move faster – and further apart – substances expand – used in a thermometer. Average Ek
Viscosity • Viscosity is a measure of how thick (viscous) and sticky a liquid is. • Viscosity reduces the ability of a liquid to flow. • Liquids that flow readily (water) have a low viscosity. • Viscosity is a function of (depends on) the attractive forces of the molecules of the liquid. • Strong forces – high viscosity • Temperature also greatly affects viscosity: as temperature increases, viscosity decreases. Kinetic energy enables particles to overcome forces.
