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Chemical Fundamentals

Chemical Fundamentals. September 10 th , 2012. Review. All living things are composed of matter Atom – consists of a nucleus, positively charged protons and neutral neutrons, surrounded by tiny negatively charged electrons Atom number = number of protons in the nucleus

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Chemical Fundamentals

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  1. Chemical Fundamentals September 10th, 2012

  2. Review • All living things are composed of matter • Atom – consists of a nucleus, positively charged protons and neutral neutrons, surrounded by tiny negatively charged electrons • Atom number = number of protons in the nucleus • Mass number = number of protons and neutrons • Elements arranged in order of increasing atomic number

  3. Isotopes • In the natural environment, most elements contain atoms with varying number of neutrons – these atoms are called isotopes • Isotopes  Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass • Example: Uranium 238 (elemental form) and Uranium 235 (isotope form) • Radioisotopes radioactive! Where the nucleus breaks apart or decays

  4. Isotopes Continued… • Radioactivity – leaves behind new element, release of a number of subatomic particles, and radiation • Example  Carbon-12 and 13 are stable isotopes, while Carbon-14 is radioactive and decays into Nitrogen-14 • Half-life  how long it takes for one half of the atoms in a sample to decay. For example: Beryllium has a half life of 13.81 seconds. After 13.81 seconds, half of the Beryllium turns into Boron

  5. Water! • Consists of 2 hydrogen atoms and 1 oxygen atom • Polar covalent bond: the electrons shared by the atoms spend a greater amount of time, on the average, closer to the Oxygen nucleus than the Hydrogen • Highly polar molecule – its polarity permits it to form chemical bonds with other molecules and ions • More substances dissolve in water than other liquid. Some are easier to dissolve than others. Those that dissolve very little are insoluble

  6. Water Continued… • Miscible liquids that dissolve into one another • Immiscible  liquid that form separate layers instead of dissolving • Example: Gasoline and oil are immiscible with water, but are miscible with each other • Non-polar molecules are said to be hydrophobic (water-hating) • Polar molecules are said to be hydrophilic (water-loving)

  7. Acids & Bases • Pure water does not just contain H20. Instead, at about room temperature, two water molecules amongst every 550 million, react with each other. This results in an H20 molecule transferring a H+ ion to another H20 molecule, which equals to  1 OH- molecule and a H30 molecule • OH- (Hydroxide) and H30 (Hydronium) • Hydronium gives rise to the properties of acidic solutions • Hydroxide ion has the properties of a base

  8. Acids & Bases, Continued… • Acids and bases may be strong or weak – this depends on the degree of how they ionize when dissolved in water • Strong acids and strong bases completely ionize when dissolved in water • Weak acids and weak bases partially ionize in water

  9. Acids & Bases, Continued… • Reactions may take place in both ways. For example: when acetic acid is placed in water, it ionizes to hydronium and acetate ions. However, as the concentration of ions increases, the reverse reaction starts to occur, until it comes to the point where the rate of the forward and reverse reactions become equal and the solution is said to be in a state of equilibrium

  10. Characteristics of Acidic Solutions • Sour taste • Ability to turn blue litmus red • Ability to conduct electricity • pH below 7 • H+ donors • Proton donor • Examples: citric acid, stomach juice, orange juice

  11. Characteristics of Basic Solutions • Bitter taste • Slippery feel • Conduct electricity • Change the color of red litmus to blue • Increase the concentration of hydroxide ions in solution • pH above 7 • H+ acceptors • Proton acceptor • Examples: sodium hydroxide, pancreatic juice, detergent

  12. Buffers • Buffers are used by living cells to resist significant changes in pH • Buffers usually consist of conjugate acid-base pairs in equilibrium • In an acid-base neutralization, an acid and a base react to form water and salt. In order for the reaction to carry out, there must be the transfer of protons between acids and bases. Proton acceptors and proton donors are the basis for these reactions, and are also referred to as conjugate bases and acids.  • Acetic acid, acetate and hydronium ions and water conjugate acid-base pairs

  13. Buffers, Continued… • Proteins can also act as buffers. For example: hemoglobin helps to maintain a constant pH within red blood cells

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