Transcript Chapter 2 The Chemistry of Life

Chapter 2
The
Chemistry of
Life
© 2005 Jones and Bartlett Publishers
2-1 Atoms and Subatomic Particles
Atoms are the fundamental
unit of all matter.
– Atoms contain electrons,
protons, and neutrons.
Figure 2-2
Section 2-1
Elements are pure substance that contains
only one type of atom.
– 92 naturally occurring elements are known
– only about 20 are found in organisms
– Four elements in this group: carbon, oxygen,
hydrogen, and nitrogen (remember: COHN)
comprise 98% of the atoms of all living things
• The mass number of an element
– Is the sum of protons plus neutrons in the nucleus of an
atom
– Is an approximation of the atomic mass of an atom
• The atomic number of an element
– Is the number of protons
– Is unique to each element
The Periodic Table Permits Elemental
Organization
• Atoms of a given element
– May occur in different forms - one example = Isotope
• Isotopes of a given element
– Differ in the number of neutrons in the atomic
nucleus
– Have the same number of protons
• Radioactive isotopes
– Spontaneously give off particles and energy
Section 2-2 The Making of a Molecule
Atoms combine to form molecules.
– Compound: a substance made up of two or more
atoms
– Molecule: the smallest particle of a compound
that still retains the properties of that compound.
Section 2-2
Atoms bond to form more stable
configurations.
– There are two types of bonds that form
between atoms:
• Ionic
• Covalent
– Electrons are responsible for creating the
bonds that hold atoms together
Section 2-2
Ionic bonds are electrostatic attractions
between two oppositely charged particles.
– Ionic bonds form between two atoms when one
loses an electron and the other gains an electron
– This reaction creates two charged particles,
known as ions
Section 2-2
Covalent bonds are formed by the sharing of
electrons between atoms
Section 2-2
Polar covalent bonds
occur any time there
is an unequal
sharing of electrons
by two atoms
– A polar covalent
bond’s atoms bear a
slight charge—either
positive or negative
Figure 2-7
Polar Covalent Bonding In Water
Permits Hydrogen Bonding
Hydrogen bonds form between
slightly charged atoms
usually on different
molecules.
In water, the electrostatic
attractions between the
positively charged hydrogen
atoms of one water molecule
and the negatively charged
oxygen atoms form the
hydrogen bond.
Section 2-3 Water, Acids, Bases, and
Buffers
Water is vital to life for many reasons.
– Water is a major component of all cells and
organisms
– Water serves as a solvent, a transport
medium, and a lubricant.
– Water participates in many chemical
reactions.
– Water helps regulate body temperature.
Section 2-3
Water molecules split into hydrogen and
hydroxide ions. This reaction is reversible
– The ratio of water molecules to the ions, H+ and
OH-, in the human body is about 500 million: 1
– The slightest change in the hydrogen ion
concentration can alter cells and organisms,
shutting down biochemical pathways
– Humans contain several homeostatic
mechanisms to ensure a constant level of these
ions
Section 2-3
Acids are substances that add hydrogen ions to
solution; bases remove them.
–
–
–
–
Acidity is measured on the pH scale
A solution with a pH less than 7 is acidic.
A solution with a pH greater than 7 is basic.
On the pH scale, a change in one pH unit represents
a tenfold change in acidity
– Most biochemical reactions occur at pH values
between 6 and 8.
Section 2-3
Figure 2-9 The Ph Scale
Section 2-3
Homeostasis is ensured in part by buffers,
molecules that help maintain pH within a
narrow range.
– Buffers help maintain a constant pH by removing
hydrogen ions from solution when levels increase.
– Buffers give back the hydrogen ions when levels
fall.