Summary MLB 111 Notes

CHAPTER 2: THE NATURE OF WATER MOLECULES AND THE
PROPERTIES OF WATER
2.1 THE NATURE OF ATOMS
- Matter: all substances in universe that have mass and occupy space
- All matter composed of small particles called atoms

ATOMIC STRUCTURE INCLUDES A CENTRAL NUCLEUS AND
ORBITING ELECTRONS
- Nucleus formed of protons and neutrons
- Subatomic particles = electrons (- charge)

ATOMIC NUMBER
- Atomic number = number of protons (+ charge)
- Element: cannot be broken down into any other substance
- One electron for every proton = neutral – no net charge – neutral atoms

ATOMIC MASS
- Mass: amount of substance
- Weight: force of gravity exerts on a substance
- Atomic mass = number of masses of its protons and neutrons

ELECTRONS
- Positive charges in nucleus neutralised by electrons
- Located in orbitals
- Net positive charge = cation
- Negative charge = anion

ISOTOPES
- Same number of protons, different number of Neutrons
- Nuclear breakup = radioactive decay – radioactive isotopes
*read through first bit in notes not NB

,2.2 ELEMENTS FOUND IN LIVING SYSTEMS
THE PERIODIC TABLE DISPLAY ELEMENTS ACCOORDING TO ATOMIC
NUMBER AND PROPERTIES
- Outermost energy level = valence electrons
- Group 8 – noble gases
- Octet rule – 8 electrons max.
- C, H, O, N – 96.3% of weight of body
- Since water most common molecule – oxygen is most abundant element
in body
- Zn and I play large role in living processes




- Zinc (Zn)
▪ Used by great number of enzymes and proteins
▪ Associated with general genetic regulation (large number of
regulator proteins that bind to DNA contain Zn)
▪ Deficiency can lead to lack of sexual maturation and small stature
- Iodine (I)
▪ Required for biosynthesis of thyroid hormones
▪ Deficiency can lead to enlargement of thyroid gland – goiter

,2.3 THE NATURE OF CHEMICAL BONDS
- Molecule: group of atoms held together b energy in stable association
- Compound: molecule contains atoms of more than one element




- Covalent bonds – can exist as single, double or triple bonds




IONIC BONDS FORM CRYSTALS
- Ionic bond: results from transfer of electrons from a metal to non-metal
in order to attain a full valence shell for both atoms – produces charged
atoms
- Ionic bonds form crystals

, COVALENT BONDS BUILD STABLE MOLECULES
- Forms when 2 atoms share one or more pairs of valence electrons –
results in no net charge, satisfies octet rule, no unpaired electrons
- Can exist as: single covalent bond (1 electron pair shared), double
covalent bond (2 electron pairs shared), triple bond (3 electron pairs
shared)
- Strength of the bond depends on the number of shared electrons
- Large number of organic compounds composed of atoms of 2/more
elements (C, H, O, N, S)
- C – 4 valence electrons – can form 4 covalent bonds with variety of
atoms (CHON) and Is found in many different kinds of compounds

POLAR AND NONPOLAR COVALENT BONDS
- Depends on electron affinity (electronegativity) of atoms, sharing of
valence electrons in a covalent bond can either be equal or bias
- covalent bonds formed between atoms of equal electronegativity –
electrons shared equally
- Covalent bonds formed between atoms of far different electronegativity
– electrons not equally shared (closer to atom with greater
electronegativity)
- Unequal distribution of electrons results in:
▪ Regions of partial negative charge - near more electronegative
atom
▪ Regions of partial positive charge – near less electronegative
atom
- Covalent bonds form between:
▪ Identical atoms/atoms of equal electronegativity = non-polar
▪ Atoms differ greatly in electronegativity = polar
- Difference in EN > and = 0.5 – polar covalent
- Difference in EN < 0.5 – non-polar covalent
- From top to bottom in table 2.2 goes from
partially negative to partially positive