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Essential Chemistry for Biology
Matter is made of atoms
Elements found in biological molecules (Fig. 2.2)
Atomic structure (Fig. 2.4)
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
Atomic mass
• Mass of subatomic particles– Protons = 1 unit– Neutrons = 1 unit– Electron = 0 (not zero, but really, really, small)
• Mass = # protons + # neutrons• Different masses of the same element are
called isotopes
Some isotopes are unstable
• Radioisotopes decay and emit particles until they are stable
• Carbon-14 “decays” to Nitrogen 14
Radioisotopes decay at a fixed rate
• 50% of C-14 in any substance will decay in 5700 years
• If we measure the amount of C-14 and the amount of C-12 in a sample we could estimate the age of the sample (Carbon dating)
• Other isotopes are used for dating rocks millions or billions of years old
Potassium-Argon Decay (NIB)
Electrons Exist in Shells (NIB)
Atomic charges
• The overall charge of an atom = # protons - # electrons
• 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
Four Elements (Fig. 2.5)
Bonds
• Atoms can form bonds with other atoms to form molecules
• Two types of bonds
1. Covalent
• Two atoms share their outer electrons forming a bond
• H2O, CO2, NH3, O2 are held together by covalent bonds
Molecular Compounds with Covalent Bonds (Fig. 2.7)
2. Ionic Bonds (Fig. 2.6)A positive ion (metal) can bond with a negative ion (non-metal) to form an ionic bond.
Sodium (Na) and chlorine (Cl) form ionic bonds in table salt
Intermolecular Forces
• Polar molecules have a slightly positive end and a slightly negative end
• Polar molecules form weak polar bonds with other polar molecules
• Polar molecules containing hydrogen will form hydrogen bonds with other polar molecules.
• Water is a polar molecule.
Hydrogen Bonds (2.8)
Hydrogen Bonds (Figure 2.13)
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
Water transport in a tree (Fig 2.9)
Water is a solvent for ionic compounds (Fig. 2.14)
Surface Tension
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 < pH < 7• Bases - 7 < pH < 14• Water pH = 7 (Neutral)
pH Scale (Fig. 2.16)