Transcript Essential Chemistry for Biology - Saint Demetrios Astoria School

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
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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)