Essential Chemistry for Biology

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Essential Chemistry for Biology
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Atoms, Molecules and Life
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Matter is made of atoms
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Elements found in biological molecules (Fig. 2.2)

• Carbon C
• Hydrogen H
• Oxygen O
• Nitrogen N
• Calcium
• Phosphorus
• Potassium
• Sulfur

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Atomic structure (Fig. 2.4)
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Atomic Number

• Atomic number protons
• Each element has its own number of protons
• Carbon has 6 protons. Oxygen has 8.
• If you change the number of protons you change
  the element
• If you add another proton to carbon it will have
  7 which makes it nitrogen

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Atomic mass

• Mass of subatomic particles
• Protons 1 a.m.u.
• Neutrons 1 a.m.u.
• Electron 0 (not zero, but really, really,
  small)
• Mass protons neutrons
• Different masses of the same element are called
  isotopes

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Some isotopes are unstable

• Unstable isotopes decay and give particles until
  they are stable
• They are radioactive
• Carbon-14 decays to Nitrogen 14

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Radioisotopes decay at a fixed rate

• ½ of a given amount C-14 will decay in 5700
  years
• If we can measure the amount of C-14 and the
  amount of C-12 in a sample we could estimate the
  age of the sample
• This called Carbon dating
• While carbon dating is useful for dating young
  artifacts, other isotopes are used for dating
  rocks millions or billions of years old

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Potassium-Argon Decay (NIB)
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Electrons Exist in Shells (NIB)
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Atomic charges

• The overall charge of an atom
• protons - electrons
• Hydrogen normally has 1 proton and 1 electron
  (charge is 0 or neutral)
• Remove one electron what is the charge?
• 1
• Chlorine normally has 17 protons and 17
  electrons. (charge 0)
• Add one electron what is the charge?
• -1

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Ions

• If an atom has a () or () charge it is an ion
• Metals normally form () ions
• Non-metals form () ions
• Ions can only be formed by changing the number of
  electrons in an atom

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Four Elements (Fig. 2.5)
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Bonds

• Atoms can form bonds with other atoms to form
  molecules
• Three types of bonds
• Covalent
• Ionic
• Hydrogen

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Covalent

• Two atoms share their outer electrons forming a
  bond
• Some elements can share more than one electron
• H 1 bond
• Oxygen 2 bonds
• Nitrogen 3 bonds
• Carbon 4 bonds
• Ex H2O, CO2, NH3, O2 are held together by
  covalent bonds

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Molecular Compounds with Covalent Bonds (Fig. 2.7)
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Ionic Bonds (Fig. 2.6)

• A positive ion (metal) can bond with a negative
  ion (non-metal) to form an ionic bond.

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Sodium (Na) and chlorine (Cl) form ionic bonds in
table salt
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Hydrogen Bonds

• Some molecules have a slightly positive end and a
  slightly negative end.
• We call these polar molecules.
• Polar molecules will form weak hydrogen bonds
  with other polar molecules.
• Water is a polar molecule.

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Hydrogen Bonds (Figure 2.13)
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Water is important to life

• Forms hydrogen bonds with itself and other polar
  molecules (Hydrophilic)
• Forms a solution for many chemical reactions
  inside our cells
• Moderates temperature
• Required for photosynthesis

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Water transport in a tree (Fig 2.9)
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Water is a solvent for ionic compounds (Fig. 2.14)
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Surface Tension
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Acids and Bases

• Acids are molecules that give up a positive
  hydrogen ion (H)
• Bases are molecules that accept a positive
  hydrogen ion (H)
• How readily an atom accepts or donates a hydrogen
  is indicated by its pH
• Acids - 0 lt pH lt 7
• Bases - 7 lt pH lt 14
• Water pH 7 (Neutral)

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pH Scale (Fig. 2.16)