Biology 102 Chapter 3 - Chemistry: The Basics
Chemistry of Life
Living things are composed of matter and function through countless chemical reactions.
Matter
Anything that takes up space and has mass
● Matter is made out of elements: substances that can't be broken down into other
substances by chemical reactions.
● Some matter is composed of multiple elements
○ Compounds have characteristics different from their elements.
About 25 of 94 natural elements are essential to life. 96% of living matter is composed of:
● Hydrogen (H) ● Nitrogen (N)
● Oxygen (O) ● Carbon (C)
Atoms
The smallest unit of an element
An element's properties depend on the structure of its atoms.
Atomic number: number of protons
Atomic mass: number of protons + number of neutrons
Subatomic particles: protons, neutrons, and electrons
An element is defined by the number of protons in its atoms.
Isotopes
All atoms of an element have the same
number of protons but may differ in a number
of neutrons.
Isotopes are two atoms of an element that
differ in # of neutrons
1
, Biology 102 Chapter 3 - Chemistry: The Basics
Molecules
Molecules form when two or more atoms come together.
Different types of bonds cause molecules to form.
Important bonds in biology:
1. Ionic Bonds:
● Ions: atoms with an electric
charge.
● These form when atoms lose or
gain electrons.
2. Covalent Bonds:
● Other molecules form by sharing
electrons
● A Covalent bond is formed.
● These bonds form the majority of
biological molecules.
3. Hydrogen Bonds:
● A hydrogen bond forms when a
hydrogen atom covalently bonded
to one electronegative atom is
also "attracted" to another
electronegative atom.
● Water molecules love to hydrogen
bond with each other.
2
Chemistry of Life
Living things are composed of matter and function through countless chemical reactions.
Matter
Anything that takes up space and has mass
● Matter is made out of elements: substances that can't be broken down into other
substances by chemical reactions.
● Some matter is composed of multiple elements
○ Compounds have characteristics different from their elements.
About 25 of 94 natural elements are essential to life. 96% of living matter is composed of:
● Hydrogen (H) ● Nitrogen (N)
● Oxygen (O) ● Carbon (C)
Atoms
The smallest unit of an element
An element's properties depend on the structure of its atoms.
Atomic number: number of protons
Atomic mass: number of protons + number of neutrons
Subatomic particles: protons, neutrons, and electrons
An element is defined by the number of protons in its atoms.
Isotopes
All atoms of an element have the same
number of protons but may differ in a number
of neutrons.
Isotopes are two atoms of an element that
differ in # of neutrons
1
, Biology 102 Chapter 3 - Chemistry: The Basics
Molecules
Molecules form when two or more atoms come together.
Different types of bonds cause molecules to form.
Important bonds in biology:
1. Ionic Bonds:
● Ions: atoms with an electric
charge.
● These form when atoms lose or
gain electrons.
2. Covalent Bonds:
● Other molecules form by sharing
electrons
● A Covalent bond is formed.
● These bonds form the majority of
biological molecules.
3. Hydrogen Bonds:
● A hydrogen bond forms when a
hydrogen atom covalently bonded
to one electronegative atom is
also "attracted" to another
electronegative atom.
● Water molecules love to hydrogen
bond with each other.
2
