The Chemical Context of Life
A.
B.
C.
D.
Atomic structure
The periodic table
Chemical bonding
Important elements in living organisms
A.
Atomic Structure
Matter
– Anything that takes up space and has mass
Atom
– The smallest stable particle of matter
– Composed of protons, neutrons, and electrons
A.
Atomic Structure
Protons
– Positively charged
– Atomic mass  1 atomic mass unit
– Located in the nucleus of an atom
Neutrons
– Electrically neutral
– Atomic mass  1 atomic mass unit
– Located in the nucleus of an atom
A.
Atomic Structure
Electrons
– Negatively charged
– Atomic mass: very small, almost negligible
– Located in electron shells (orbitals) around the
nucleus
In a neutral atom, the number of electrons and
protons is the same
Atoms can lose or gain electrons during
chemical bonding
A.
Atomic Structure
Element
– A substance composed of only a single type of atom
– Atomic number of an element
• The number of protons in its atoms
• The atomic number is the same for all atoms of an
element
– Mass number of an element
• The number of protons plus the number of neutrons in its
atoms
• The atoms of an element may have a variable number of
neutrons
A.
Atomic Structure
Isotopes of an element
– Different forms of an element with the same atomic
number but with different mass numbers
– The atoms of some isotopes are stable
– Other isotopes are radioactive, having unstable
atoms that spontaneously break apart (decay) to
form other atoms
– When radioactive atoms decay, energy is released
A.
Atomic Structure
For example, carbon has three isotopes
– Carbon-12, with 6 protons and 6 neutrons, is the
most common form of carbon
– Carbon-13, with 6 protons and 7 neutrons,
is stable (non-radioactive) and rare
– Carbon-14, with 6 protons and 8 neutrons,
is unstable (radioactive) and rare
B.
The Periodic Table
In the periodic table
– Elements are listed in order of their atomic numbers
– Elements are designated by standard one or twoletter abbreviations
– Elements in the same vertical column often have
very similar chemical bonding properties
C.
Chemical Bonding
Chemical bonding occurs when two or more atoms
combine
Atoms combine by exchanging or sharing electrons in
their outermost electron shell
Chemical compound
– Formed when the atoms of two or more different elements
combine by chemical bonding
– Properties of a compound are usually very different than
those of its elements
C.
Chemical Bonding
Ionic bonds
– Formed when electrons are completely transferred
from one atom to another
– The atom that gains electrons becomes a negative
ion (anion)
– The atom that loses electrons becomes a positive
ion (cation)
– Example: Sodium chloride
Na + Cl  Na+ Cl–
C.
Chemical Bonding
Covalent bonds
– Form when two atoms share one or more pairs of
electrons
– Molecule: consists of two or more atoms that are
joined by covalent bonding
– Covalent bonds are generally more stable than ionic
bonds in aqueous (water) solution
C.
Chemical Bonding
Other types of atomic & molecular interactions
– Polar interactions
• Attraction between partially charged (polar) molecules
and other polar or charged molecules
• Similar to ionic bonding
– Hydrogen bonding
• Interaction between a hydrogen atom and two strong
electronegative groups
– Hydrophobic interactions
• Attraction between molecules that are insoluble in water
D.
Important Elements
See table in the textbook
Major covalent constituents of biomolecules:
CHNOPS