CHAPTER 2 (39-50; 66-69; 78-79)
Polymeric molecules- chains of chemical subunits linked end to end
Properties enable cells & organism to grow and reproduce
CHEMICAL BONDS
Cells are made of atoms
Elements – what matter is made of; hydrogen and carbon can’t be broken down by chemical means
Atom – smallest particle of element; retains its properties
At center is nucleus – positively charged; has the number of protons
Surrounded by negatively charged electrons by electrostatic attraction
Electrons is equal to protons
Nucleus has to subatomic particles:
Protons- positively charged; (atomic number)
Neutrons- neutrally charged; same mass as protons
If too many or too few, may disintegrate by radioactive decay
Don’t alter chemical properties of atom
Isotope – different number of neutrons, same protons
Atomic Number / Molecular Weight - protons + neutrons
Expressed in daltons
Living organisms are made of:
Carbon, Hydrogen, Nitrogen, Oxygen
Outermost electrons determine how atoms interact
Limit to the amount of electrons that can orbit in the electron shell
Innermost shell can hold 2 electrons
Second shell can hold up to 8 electrons
Third shell up to 8 electrons
Fourth shell up to 18 electrons
Fifth shell up to 18 electrons
Atoms with more than 4 shells are rare in biological molecules
Atom with outermost shell completely filled is stable
Chemically unreactive
Ex: Helium (2) ; Neon (10) ; Argon (18)
Not Ex: Hydrogen (1) – halfway filled = reactive
Atoms in living things are incompletely filled in outer shell
Able to react with other atoms to form molecules
Chemical bonds to stabilize electrons
Ionic – electrons are donated by one atom to another
Covalent – electrons share a pair of electrons
The number of electrons an atom must acquire or lose to fill outer shell determines the number of bonds an atom can make.
Atoms in the same vertical column must gain or lose the same number of electrons
Covalent bonds form by the sharing of electrons
Molecule – atoms held together by covalent bonds (shared electrons)
Bond length – the attractive and repulsive force in balance with nuclei separation
Bond between equal or near equal electronegativities are non-polar
Different types of covalent bonds
Single bonds – sharing of 2 electrons, 1 donated by each atom
Allows rotation
Double bond – sharing of more than one pair of electrons
Shorter & stronger than single bonds
Have a characteristic effect on 3D geometry of molecules
Prevents rotation = ridged, less flexible structure
Polar Covalent Bonds – electrons are shared unequally
Allow molecules to interact through electrical forces
Polar – the positive charge is concentrated toward the positive pole and the negative charge is concentrated toward the negative pole
Covalent bonds vary in strength
Bond strength- measured by the amount of strength that must be supplied to break the bond (kj/mole)
In living organism- usually not broken because enzymes
Highly specialized protein catalyst
Much stronger than ionic bonds when WATER is present
Ionic bonds form by the gain and loss of electrons
Ionic bonds- formed between atoms that can fill outer shell by donating electrons or accepting electrons
Salts- ions held together by ionic bonds and NOT molecules highly soluble in water; break apart
(NaCl – Na+ Cl-
Bonds between unequal electronegativities are polar, or ionic
Cations – positive ions
Anion – negative ions
Noncovalent Bonds help bring molecules together
Noncovalent bonds – transient interactions b/t molecules
Individually weak
Energies create an effective force b.t molecules
Electrostatic attraction – form of noncovalent bonding
Strongest when the atoms are fully charged
Weaker with molecules with polar covalent bonds
Hydrogen bonds are important for noncovalent bonds
Hydrogen bonds – when a positively charged (H) comes close to a negative charged (O or N) creates a weak electrical
