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Chemical Bonds

Chemical Bonds. Covalent Bond Non-polar vs. Polar Ionic Bond Hydrogen Bond Van der Waals Interactions. Strongest Weakest. Different Types of Bonds. In a covalent bond, two atoms share an electron. If two atoms share two electrons, the bond is called a double bond. C-H , O-H , H-H

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Chemical Bonds

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  1. Chemical Bonds

  2. Covalent Bond Non-polar vs. Polar Ionic Bond Hydrogen Bond Van der Waals Interactions Strongest Weakest Different Types of Bonds

  3. In a covalent bond, two atoms share an electron. If two atoms share two electrons, the bond is called a double bond. C-H , O-H , H-H O=O , C=C Covalent Bonds

  4. Covalent Bonds • The only electrons that are shared between atoms are the valence electrons. • Valence electrons – the electrons found in the outermost shell of an atom

  5. Non-polar vs. Polar Covalent • The polarity of a covalent bond is based on the electronegativity of each atom. • If the electrons are shared equally, the bond is non-polar. • If the electrons are not shared equally, i.e. one atom pulls the electrons more than the other, a polar bond is formed.

  6. Ionic Bonds • In ionic bonds, one atom gives up a valence electron to another atom. • Called ionic compounds or salts • The atom losing the electron becomes positively charged. • The atom gaining the electron becomes negatively charged. • Ex. Table Salt NaCl = Na+-Cl

  7. Hydrogen Bond • Weak chemical bond • Very important to the chemistry of life • Occurs when one hydrogen atom covalently bonded to another electronegative atom is attracted to another electronegative atom. • Usually oxygen or nitrogen

  8. Van der Waals Interactions • Occur because electrons are not stationary. • Occur only when atoms are close together. • Atoms have positive and negative regions for brief moments.

  9. The Wonderful Properties of Water

  10. Properties of Water • Adhesion • Cohesion • Surface Tension • Polarity • High Specific Heat

  11. Adhesion • Adhesion = the clinging of one molecule to another • Ex. Adhesion of water to cell wall in plants helps fight gravity.

  12. Cohesion • The ability of water molecules to hold one to one another • Caused by H-bonds between the oxygen of one water molecules and the H of another water molecule

  13. Surface Tension • The measure of how difficult it is to stretch or break the surface of a liquid. • Because of waters cohesive property, water has a high surface tension. • Ex. Water striders are able to walk on ponds because of surface tension.

  14. Polarity • Results in Hydrogen bonding between water molecules • Hydrogen has a slightly positive charge. • Oxygen has a slightly negative charge. • This polarity makes water excellent at dissolving ions.

  15. Specific Heat • Specific Heat = the amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1°C • Specific Heat of water = 1 calorie/g/°C • Water has a high specific heat • Ethyl alcohol = 0.6 cal/g/°C

  16. Specific Heat • Since water has a high specific heat, it changes it’s temperature less. • This high specific heat is a result of the hydrogen bonds between the different water molecules. • Water has a high boiling point. • Is a strong evaporative coolant. • Less Dense as a solid. (Ice floats)

  17. Hydrophilic vs. Hydrophobic • Hydrophilic – water loving • Hydrophobic – water fearing • Hydrophilic molecules are polar and are ions. • Ex. Na+, NH3 • Hydrophobic molecules are non-polar and are not ions. • Ex. Fats and oils

  18. Macromolecules • Some larger molecules can have hydrophilic and hydrophobic portions. • These molecules will orient themselves in specific ways when placed into water.

  19. How are these properties make life on Earth possible?

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