Download Ch. 2 Chemical Basis of Life

Ch. 2
Chemical Basis of Life
Atomic Structure
!  Nucleus
!  Protons (p+)
!  Neutrons (n0)
!  Outside of
nucleus
!  Electrons (e-)
Figure 2.1
Atomic Structure of
Smallest Atoms
Figure 2.2
Identifying Elements
!  Atomic number- equal to the number
of protons that the atom contains
!  Atomic mass number- sum of the
protons and neutrons
Isotopes and Atomic
Weight
!  Isotopes
!  Have the same number of protons
!  Vary in number of neutrons
Figure 2.3
Isotopes and Atomic
Weight
!  Atomic weight
!  Close to mass number of most
abundant isotope
!  Atomic weight reflects natural
isotope variation
Molecules and
Compounds
!  Molecule—two or more like atoms combined
chemically
!  Compound—two or more different atoms
combined chemically
Figure 2.4
Chemical Reactions
!  Atoms are united by chemical bonds
!  Atoms dissociate from other atoms
when chemical bonds are broken
Electrons and Bonding
!  Electrons occupy energy levels called
electron shells
!  Electrons closest to the nucleus are most
strongly attracted
!  Each shell has distinct properties
!  The number of electrons has an upper
limit
!  Shells closest to the nucleus fill first
Bonding
!  Electrons occupy energy levels called
electron shells
!  Bonding involves interactions
between electrons in the valence shell
(outer shell).
!  All atoms want a full outer shell- 8
electrons
Ionic Bonds
!  Ionic bonds: Form when electrons
are completely transferred from one
atom to another
!  Ions: Charged particles
!  Anions: negative
! Cations: positive
Ionic Bonds
Na
Cl
Sodium atom (Na)
(11p+; 12n0; 11e–)
Chlorine atom (Cl)
(17p+; 18n0; 17e–)
+
–
Na
Cl
Sodium ion (Na+)
Chloride ion (Cl–)
Sodium chloride (NaCl)
Figure 2.6
Ionic Bonds
Na
Cl
Sodium atom (Na)
(11p+; 12n0; 11e–)
Chlorine atom (Cl)
(17p+; 18n0; 17e–)
Figure 2.6, step 1
Ionic Bonds
Na
Cl
Sodium atom (Na)
(11p+; 12n0; 11e–)
Chlorine atom (Cl)
(17p+; 18n0; 17e–)
Figure 2.6, step 2
Ionic Bonds
Na
Cl
Sodium atom (Na)
(11p+; 12n0; 11e–)
Chlorine atom (Cl)
(17p+; 18n0; 17e–)
+
–
Na
Cl
Sodium ion (Na+)
Chloride ion (Cl–)
Sodium chloride (NaCl)
Figure 2.6, step 3
Covalent Bonds
!  Covalent bonds: Atoms
get “full” outer shell by
sharing electrons
!  Single covalent bonds
share one pair of
electrons
!  Double covalent
bonds share two pairs
of electrons
Examples of Covalent
Bonds
Figure 2.7a
Examples of Covalent
Bonds
Figure 2.7b
Examples of Covalent
Bonds
Figure 2.7c
Polarity
!  Non-polar
covalently bonded
molecule:
electrically neutral
as a molecule
!  Polar covalently
bonded molecule:
has a positive and
negative side
Figure 2.8
Chemical Bonds
!  Hydrogen bonds: weak chemical bonds in
which hydrogen is attracted to the
negative portion of a polar molecule,
providing attraction between molecules.
Patterns of Chemical
Reactions
!  Synthesis reaction (A + BàAB)
!  Atoms or molecules combine
!  Energy is absorbed for bond formation
!  Decomposition reaction (ABàA + B)
!  Molecule is broken down
!  Chemical energy is released
Synthesis and
Decomposition Reactions
Figure 2.10a
Synthesis and Decomposition
Reactions
Figure 2.10b
Patterns of Chemical
Reactions
!  Exchange reaction (AB + CàAC + B)
!  Involves both synthesis and
decomposition reactions
!  Switch is made between molecule parts
and different molecules are made
Patterns of Chemical
Reactions
Figure 2.10c