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Bonding and Structure

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  • 1. Intramolecular bonding
  • 2. Intramolecular bonding Learning objectives • Describe the trends in the periodic table • Understand and predict the formation of ionic bonds • Understand and predict covalent bonds • Describe electronegativity • Describe molecular shape, including the Valence Shell Electron Pair Repulsion (VSEPR) model
  • 3. Intramolecular bonding Problem statement • Why is water so important to life? – To answer this question, we need to delve into the fundamental aspects of bonding in order to explain some of the unique properties of water. • Our body is made up of approximately 80 percent water. Salts are essential in our body to create the right balance – why is this?
  • 4. Intramolecular bonding The periodic table • Consider the periodic table to understand how atoms are bonded to one another.
  • 5. Intramolecular bonding Bonding: caring and sharing • What do the group numbers tell us? – The group numbers tell us the number of electrons in the outer shell. – These valence electrons form bonds with other atoms. – Atoms combine to become more stable. • Bonding occurs in different ways, Click the depending on the atoms involved: magnifying glass. – Covalent – Polar covalent – Ionic
  • 6. Intramolecular bonding Bonding: caring and sharing • What do the group numbers tell us? – The group numbers tell us the number of electrons in the outer shell. – These valence electrons form bonds with other atoms. – Atoms combine to become more stable. • Bonding occurs in different ways, Click the depending on the atoms involved: magnifying glass – Covalent – Polar covalent – Ionic
  • 7. Intramolecular bonding Covalent bonding • A covalent bond is a bond in which the atoms share electrons. • They are formed between two non-metals. • A non-polar covalent bond is a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge: – Examples: H2, N2, O2, F2, Cl2, Br2, I2 • A polar covalent bond is formed when electrons are unequally shared between two atoms. – Examples: hydrogen-oxygen bond in the water molecule Consider the question before • Do you think methane has polar or non-polar continuing. covalent bonding?
  • 8. Intramolecular bonding Ionic bond • Ionic bonds are usually formed between metals and non-metals. • An ionic compound is composed of a positive and a negative ion that are combined so that the number of positive and negative charges are equal. • Sodium is in group 1A – It loses an electron to become a cation. • Chlorine is in group 7A – It takes an electron to become an anion. Sodium Chloride
  • 9. Intramolecular bonding Electronegativity • Electronegativity is the ability of an atom in a molecule to attract electrons in the chemical bond towards it. • Electronegativity is affected by both the atomic weight and the distance of the valence electrons from the nucleus of the atom. • The electronegativity provides one way to tell the difference between a polar and non-polar covalent bond: - If the electronegativities are equal, the compound is non-polar. - If the electronegativities are not equal, the compound is polar. - If the difference in electronegativities are between: • 1.7 to 4.0, it is an ionic bond ▪ 0.0 to 0.3, it is a non-polar covalent bond Click the ▪ 0.3 to 1.7, it is a polar covalent bond magnifying glass.
  • 10. Intramolecular bonding Bonding: caring and sharing • What do the group numbers tell us? – The group numbers tell us the number of electrons in the outer shell. – These valence electrons form bonds with other atoms. – Atoms combine to become more stable. • Bonding occurs in different ways, Click the depending on the atoms involved: magnifying glass – Covalent – Polar covalent – Ionic
  • 11. Intramolecular bonding Exercises • Use your mouse to click the correct cell or cells in each column. You will need to refer to an electronegativity periodic table to complete the first table.
  • 12. Intramolecular bonding Answer
  • 13. PROPERTIESAllow user to leave interaction: AnytimeShow ‘Next Slide’ Button: Show alwaysCompletion Button Label: Next Slide
  • 14. Intramolecular bonding The universal solvent • Consider how salt and water mix. – We know that water is comprised of a polar covalent molecule made up of two hydrogen atoms, which have a partial positive charge, and a single atom of oxygen, which has a partial negative charge. – Looking at the positions in the periodic table of Na and Cl and understanding the electronegativity difference, we can establish that sodium chloride is ionic. – Water molecules collide with NaCl and the polar ends of the water molecules attract oppositely charged Click the ions strongly enough to pull them away from their magnifying glass. ionic crystal lattice. – When this happens, the forces on the molecules are stronger than the bond that holds the sodium and chloride together, so the ions separate, and the sodium chloride dissolves.
  • 15. Intramolecular bonding The universal solvent • Consider how salt and water mix. – We know that water is comprised of a polar covalent molecule made up of two hydrogen atoms, which have a partial positive charge, and a single atom of oxygen, which has a partial negative charge. – Looking at the positions in the periodic table of Na and Cl and understanding the electronegativity difference, we can establish that sodium chloride is ionic. – Water molecules collide with NaCl and the polar ends of the water molecules attract oppositely charged Click the ions strongly enough to pull them away from their magnifying glass ionic crystal lattice. – When this happens, the forces on the molecules are stronger than the bond that holds the sodium and chloride together, so the ions separate, and the sodium chloride dissolves.
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  • 18. Intermolecular bonding
  • 19. Intermolecular bonding Learning objectives • Predict physical and chemical properties of molecules • Explain the overall structure of water
  • 20. Intermolecular bonding Problem statement • ‘Hot and cold’ • Can we use bonding interactions between molecules to understand why: – Solid metals sink in liquid metal, but ice floats in water? – Water has a high boiling point?
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  • 22. Intermolecular bonding Why does ice float? • One interesting property of water is that its solid form is less dense than its liquid form. • How does the chemical bonding in water explain its properties?
  • 23. Intermolecular bonding Intermolecular bonding in water • The water molecule has two important properties that underlie its importance to life. – It is polar. – It is highly cohesive. • Why is the water molecule so cohesive?
  • 24. Intermolecular bonding Hydrogen bonding • The most important property of water is the ability to form hydrogen bonds. How strong or weak are they, and what effect will they have on the density of ice? • Hydrogen bonds are weak attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule. • The small size of hydrogen, along with the shape and polarity of the water molecule, adds up to a relatively strong attraction between water molecules. • Hydrogen bonding is the strongest intermolecular force, and it plays an important role in the formation of ice.
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  • 26. PROPERTIESAllow user to leave interaction: AnytimeShow ‘Next Slide’ Button: Show alwaysCompletion Button Label: Next Slide
  • 27. PROPERTIESAllow user to leave interaction: AnytimeShow ‘Next Slide’ Button: Show alwaysCompletion Button Label: Next Slide
  • 28. Intermolecular bonding You have reached the end of this presentation. Please close this window.
  • 29. Case studies
  • 30. Case studies Learning objective • Explain how an understanding of intermolecular forces can help us explain: – Why oil and water do not mix – Why drug solubility is critical for activity in the body
  • 31. Case studies Problem statements • How would you clean up an oil spill? • Some drugs have limited water solubility – how do they get into your body and act?
  • 32. Case studies The Exxon Valdez oil spill • On 24 March 1989, the Exxon Valdez oil tanker scraped along a rocky ocean reef in Alaska, cutting open the hull of the ship. Thousands of tonnes of oil spilled into the ocean − enough to fill a football stadium. • How was this cleaned up?
  • 33. Case studies Why don’t oil and water mix? • Water is held together by hydrogen bonds and can interact efficiently with anything that has well-developed permanent charges. • Oils, however, are made up of C and H atoms, which are non-ionic and non-polar. These molecules interact by London or van der Waals dispersion forces. • Therefore, the interaction between oil and water molecules is not strong. – Oil cannot hydrogen bond because it is non-polar. – Water cant form strong London forces to the oil because it has a different polarisability. • A second issue is that water molecules are much smaller than most other molecules, so to accommodate oil molecules, many water molecules have to have their hydrogen bonds broken.
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  • 35. Case studies Water and oil in biology • This difference between non-polar ‘hydrophobic’ and polar ‘hydrophilic’ molecules is exploited in biology. • Fats (i.e. oils) are used for storage and need to remain in a cell. • Sugars, which need to be moved quickly around the body, are very hydrophilic. • Cell membranes are formed by amphiphiles, with one end hydrophilic and the other oily (hydrophobic). • Transmembrane proteins are anchored in the cell membrane by having hydrophobic sidegroups. Globular proteins have large amounts of hydrophobic sidegroups that make them fold with these on the inside, away from the water.
  • 36. Case studies Cleaning up the oil spill • In the case of the Exxon Valdez oil spill, the first clean-up response was through the use of a dispersant, a surfactant and solvent mixture. • This was applied using a helicopter and was quite successful, reducing 113,400 litres of oil to 1,134 litres of removable residue. • However, there was not enough wave action to mix the dispersant with the oil in the water, so this approach was discontinued, and booms and skimmers were then used to mechanically clean up the oil – again using the fact that oil and water do not mix.
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