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Bonding & Molecular Structure

This overview explores the key concepts of bonding and molecular structure in physical science, focusing on water's unique properties. We delve into the types of bonds, including covalent intramolecular bonds between hydrogen and oxygen, and hydrogen bonds as intermolecular forces between water molecules. By examining polarity and electronegativity, we clarify why water is a dipole, exhibiting strong hydrogen bonding that results in its high boiling point. Additionally, we address the effects of temperature on kinetic energy and viscosity, crucial for understanding molecular behavior in different states.

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Bonding & Molecular Structure

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  1. Bonding & Molecular Structure Physical Science K Warne

  2. Atoms and molecules (simple and giant)

  3. 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

  4. 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”.

  5. 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.

  6. 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.

  7. . . : X . . . . . : X . . . IMF vs Mp & Bp Mp & Bp increases with SIZE and molecule MASS

  8. 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

  9. 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

  10. 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

  11. 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.

  12. Bonding & Molecular Structure

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