BIO 202 Lecture Notes - Lecture 1: Subatomic Particle, Covalent Bond, Relative Atomic Mass
7 Aug 2018
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• Sp17 BIO 202.01 Midterm 1 Learning Objectives
Chapter 2: The Chemical Context of Life
• Atom- The smallest unit of matter that retains the properties of an element.
• Element- A substance that cannot be broken down by chemical reactions.
• Molecule- Two or more atoms joined chemically.
• Compound- A substance containing two or more different elements combined in a fixed
ratio.
• Carbon, Hydrogen, Oxygen, Nitrogen make up all living things.
• Proton- A subatomic particle with a single positive charge and a mass of 1 amu, or 1
Dalton, or 1.7x10-24 g.
• Neutron- A subatomic particle with a neutral charge and a mass of 1 amu, or 1 Dalton, or
1.7x10-24 g.
• Atomic number- Number of protons
• Atomic weight/Mass number- Number of protons and neutrons in Daltons. (Atomic
weight is average mass of each element based on isotope abundance)
• A dense positive nucleus, with a cloud of electrons orbiting around it. Electrons form
“shells” around nucleus, with a different number orbitals in each (1, 4, 4 in valence for
first 3 periods).
o An atom’s valence configuration affects its reactivity. Lone electrons in the
valence shell have the capacity to form covalent bonds.
• Non-polar covalent bonds- Sharing of a pair of valence electrons by two atoms of equal
electronegativity.
• Polar covalent bonds- Sharing of a pair of valence electrons by two atoms of different
electronegativity, where the electrons are slightly drawn towards the more
electronegative atom, creating a partial negative charge.
• Ionic bonds- Transfer of an electron from one atom to another, usually between a metal
and a gas, forming ions of both atoms. The attraction between oppositely charged ions
forms a “bond.”
• Hydrogen bonds- A bond of attraction between a hydrogen covalently bonded to an
electronegative atom and another electronegative atom (usually O or N).
• Van der Waals interactions- A weak attraction that results from an asymmetric
distribution of electrons in the valence shell (combination of these interactions can form a
strong attraction, i.e. gecko toe hairs and wall surface).
Chapter 3: Water and Life
• An uneven distribution of electrons caused by the oxygen’s electronegativity pulls the
electrons towards the oxygen atom. The bent shape of the molecule distributes all the
partial negativity on the oxygen’s side and the positivity on the hydrogens’ side, making
H2O polar.
• Molecules of water are farther apart in ice, meaning there are less molecules per unit of
surface area, thus, it is less dense than water molecules which can pack together.
• Water properties:
o Cohesive behavior- Water molecules stick together because of hydrogen bonds
and van der Waals forces. Water’s polarity allows it to attract other molecules,
causing adhesion. Surface tension is caused by the pulling between molecules that
minimize the surface area of a sample.
o Ability to moderate temperature- Water can absorb or release large amounts of
heat without fluctuating too much in temperature due to its high specific heat. The
high specific heat stems from the hydrogen bonds constantly breaking and
forming between molecules. Low temperature fluctuations permit life to exist in
stable conditions. Evaporative cooling through perspiration, and then evaporation,
pulls heat off our bodies.
