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CHAPTER 2

CHAPTER 2. ATOMS, MOLECULES, AND CHEMICAL BONDS. Matter. Chemistry is the study of matter Matter takes up space and has mass Matter comes in many different forms. Chemical Elements. Cannot be broken down 92 elements occurring in nature Symbol (different languages) 2 or 3 letters

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CHAPTER 2

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  1. CHAPTER 2 ATOMS, MOLECULES, AND CHEMICAL BONDS

  2. Matter • Chemistry is the study of matter • Matter takes up space and has mass • Matter comes in many different forms

  3. Chemical Elements • Cannot be broken down • 92 elements occurring in nature • Symbol (different languages) 2 or 3 letters • 25 elements are essential to life • C, O, H, N • Ca, P, K, S • Fe, I These are the most common.

  4. Compounds Sulfuric Acid molecule • Two or more elements combined in a fixed ratio • More common than pure elements WHY? • Example: Na reacts? Cl reacts? NaCl reacts?

  5. Isotopes - different atomic forms of the same element just different # of neutrons Radioactive isotopes – unstable because the nucleus decays spontaneously by giving off particles and energy

  6. Helpful: biological tracers (plant studies, medicine, PET: positron-emission tomography) Harmful: damages cellular molecules (DNA) Half-life – time it takes for 50% of the radioactive atoms to decay

  7. Energy Levels • Why does an atom behave like it does? • How much energy will an atom possess? • Electron shells – different states of potential energy due to position in relation to nucleus (closer to nucleus, lower energy)

  8. Orbital – 3-D shape where an electron is found How many in the 1st electron shell? How many in the outermost shell? So the chemical properties of an atom depend on the number of electrons in the outermost shell.

  9. Hydrogen Bonds • a hydrogen atom covalently bonds to one electronegative atom and is attracted to another electronegative atom • Ex: water to water H2O H2O

  10. Cohesiveness Cohesion – water molecules stick together because of hydrogen bonding Surface tension – difficult to stretch or break the surface of water (beads up) Adhesion – clinging of one type of substance to another type

  11. Hydrophilic – water loving (clings to water) Capillary action – rising up a tube made of hydrophilic material (adhesion and cohesion together) Imbibition – water soaks into a porous material

  12. Moderating Temperature Specific heat – amount of energy it takes to raise 1 Kg of a substance 1oC --hydrogen bonds allow water to resist quick temperature changes

  13. Heat – amount of energy associated with the movement of atoms and molecules Temperature – measures intensity of heat (average speed of atoms and molecules)

  14. Heated water breaks hydrogen bonds • --Molecules move faster and water absorbs a lot of heat (but temp. only warms a few degrees) • Cooled water reforms hydrogen bonds • --Molecules move slower and water releases a lot of heat (but only cools a few degrees)

  15. Water requires a lot of heat to completely break all hydrogen bonds of a single water molecule so this decreases water’s tendency to evaporate • --This is what gives water a high boiling point --When water does evaporate (heat energy is carried off), the remaining liquid water is cooled. Ex: sweating

  16. Freezing of Water • Why is water less dense as a solid? • What is the significance of 4 degrees Celsius in water? --So water freezes when its molecules no longer move enough to break the hydrogen bonds

  17. Acids, Bases, and pH When water molecules bond, the H-bond shifts around from one molecule to another allowing for a Hydrogen Ion and a Hydroxide Ion Dissociation – separation of a water molecule

  18. An acid adds [H+] to a solution • A base reduces [H+] in a solution so now it has more [OH-] The product is the pH scale (potential hydrogen), which compresses the range of [H+] and [OH-] by using logarithms.

  19. An acid adds [H+] to a solution • A base reduces [H+] in a solution so now it has more [OH-] The product is the pH scale (potential hydrogen), which compresses the range of [H+] and [OH-] by using logarithms.

  20. 7 is neutral, below 7 is acidic, above 7 is basic Buffers minimize changes in[H+]and[OH-]and are usually aweak acid or aweak base Ex:Carbonic Acid acts as a buffer in our blood.

  21. Acid Rain • Below pH 5.6 • Caused by a reaction of water and sulfur oxides and nitrogen oxides in the atmosphere • Harmful effects on terrestrial and fresh water ecosystems

  22. Chemical Reactions • The process of making and breaking bonds • What are the 5 types? Synthesis Double Replacement Single Replacement Combustion Decomposition

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