BIO 181 MODULE 2, HOW PROTEINS WORK
COMPREHENSIVE STUDY GUIDE & REVISION NOTES 2026
LATEST EDITION 2026
Module 2.1 (How Atoms Form Molecules)
Objective
Describe the potential interactions between atoms and molecules
Key Point
Atoms interact to form covalent, ionic, or hydrogen bonds within or
between molecules
Atom
the smallest unit of matter that can participate in a chemical reaction,
consisting of one or more protons and some number of electrons
atoms are categorized into types called elements
organism biology
Water accounts for the majority of atoms in an organism
Carbon accounts for most of the remaining atoms
Nitrogen is almost as abundant as carbon
Bond
an attraction that holds two atoms together
covalent bond
a strong attraction that occurs when two atoms share electrons
single bond
C-C (2 shared electrons)
double bond
C=C (4 shared electrons)
Module 2: How Proteins Work 1
, triple bond
C(three lines)C (6 shared electrons)
number of atoms
H is most stable with 1 covalent bond
O is most stable with 2 covalent bonds
C is most stable with 4 covalent bonds
N is most stable with 3 covalent bonds
Molecule
a group of atoms held together by one or more covalent bonds
Sharing of bonds is not always equal
nonpolar covalent bond
polar covalent bond
Hydrogen Bond
a weak attraction between a hydrogen atom in one molecule and an atom with
a partial negative charge in another molecule
Ionization (ionic bond)
an attraction between an atom with a positive charge and an atom with a
negative charge
cation
positively charged ion
anion
negatively charged ion
Water
hydrophilic (water-loving)
Module 2: How Proteins Work 2
COMPREHENSIVE STUDY GUIDE & REVISION NOTES 2026
LATEST EDITION 2026
Module 2.1 (How Atoms Form Molecules)
Objective
Describe the potential interactions between atoms and molecules
Key Point
Atoms interact to form covalent, ionic, or hydrogen bonds within or
between molecules
Atom
the smallest unit of matter that can participate in a chemical reaction,
consisting of one or more protons and some number of electrons
atoms are categorized into types called elements
organism biology
Water accounts for the majority of atoms in an organism
Carbon accounts for most of the remaining atoms
Nitrogen is almost as abundant as carbon
Bond
an attraction that holds two atoms together
covalent bond
a strong attraction that occurs when two atoms share electrons
single bond
C-C (2 shared electrons)
double bond
C=C (4 shared electrons)
Module 2: How Proteins Work 1
, triple bond
C(three lines)C (6 shared electrons)
number of atoms
H is most stable with 1 covalent bond
O is most stable with 2 covalent bonds
C is most stable with 4 covalent bonds
N is most stable with 3 covalent bonds
Molecule
a group of atoms held together by one or more covalent bonds
Sharing of bonds is not always equal
nonpolar covalent bond
polar covalent bond
Hydrogen Bond
a weak attraction between a hydrogen atom in one molecule and an atom with
a partial negative charge in another molecule
Ionization (ionic bond)
an attraction between an atom with a positive charge and an atom with a
negative charge
cation
positively charged ion
anion
negatively charged ion
Water
hydrophilic (water-loving)
Module 2: How Proteins Work 2
