Chapter 2
Chemistry Review
Outline
Matter
Elements and compounds
Atoms and Molecules
Atomic structure
Electron configurations and chemical
properties
Molecules
Chemical bonds
Shape and function
Chemical reactions
Matter
Matter: has mass and occupies space
All
matter is composed of atoms
Fundamental
unit of Chemistry
An element is a substance that
cannot be broken down to other substances by chemical reactions.
A
kind of atom.
92
elements occur in nature.
Each
element has a one or two letter symbol.
A compound is a substance made of two or more lements
combind in a fixed ration
Ex.
Sodium chloride (NaCl).
Figure 2.2 The
emergent properties of a compound
Elements essential to
life
25
of the 92 natural elements are essntial to life.
Four
of these, carbon (C), oxygen (O),
hydrogen (H), and nitrogen (N) make up 96% of living matter.
These
make up the macromolecules that are the building block of life.
Phosphorus
(P), sulfur (S), calcium (Ca), and potassium (K), account for most of the
remaining 4%.
Trace
elements are required in minute quantities.
Iron
(Fe) is required for hemoglobin, and some enzymes.
Iodine
(I) is required to produce thyroid hormone,
Mg,
Mn, Zn & Cu help enzymes to function.
Figure 2.4 Goiter
Figure 2.3 Nitrogen
deficiency
Atomic Structure
An atom consists of an atomic
nucleus circle by an orbiting cloud of electrons.
Atomic nucleus consists of protons
and neutrons.
Protons carry a positive charge
Neutrons are uncharged
Electrons carry a negative charge
The number of protons determine the
chemical properties of an atom because it determines the number of electrons
available for chemical activity.
Figure 2.5 Two
simplified models of a helium (He) atom
Atomic Mass and Number
The atomic mass of an atom is the
sum of the masses of its protons and neutrons.
Naturally occurring atoms contain
from 1 92 protons and up to 146 neutrons.
The number of protons is referred to
as the atomic number.
Atoms with the same number of
protons (or same atomic number) have the same chemical properties, and belong
to the same element.
Units of Atomic Mass
Atomic mass is measure in daltons
(6.02 x 1023 daltons per gram)
A proton weighs 1.009 daltons (~ 1)
A neutron weighs 1.007 daltons (~ 1)
An electron weighs 0.0005 daltons (~
0)
Isotopes
Atoms
of an element that posses different number of neutrons are isotopes of that
element.
In
nature, elements may exist as a mixture of elements.
Carbon
contains 6 protons, and has three isotopes in nature . . .
Radioactive Isotopes
Radioactive
isotopes have unstable nuclei that emit energy in the form of subatomic
particles.
Ex.
14C with 6 protons and 8 neutrons.
Each
isotope has a constant rate of decay.
Rate
of decay is expressed as the half-life or the time it takes for ½ the atoms
in a sample to decay.
Example of half-life
14C has a
half-life of 5600 years.
A
sample contain 1 gram of 14C today would contain
0.5
gram after 5600 years
0.25
gram after 11,200 years
0.125
gram after 16,800 years,
Etc.
Uses of Radioactive Isotopes
Radiometric
dating of biological samples, rocks, etc.
Used
in basic research to follow molecules through biological processes.
Used
in medicine to selectively destroy cells.
Figure 2.6 Using
radioactive isotopes to study cell chemistry
Figure 2.7 A PET
scan, a medical use for radioactive isotopes
Dangers of Radioactive Isotopes
Energetic
subatomic particle emitted by radioactive substance can mutate genes and
severely damage or kill living cells.
Figure 2.8 The
Tokaimura nuclear accident
Electron configurations
Electrons determine the chemical
behavior of atoms.
Electrons do not simply circle the
atomic nucleus, but can be anywhere at a given instant.
The areas where atoms are more
likely to be are called orbitals that have a variety of shapes, depending on the
distance from the nucleus.
However, simplified models of the
atomic energy levels allow us to predict
how atoms will interact.
Only electrons are directly involved
in chemical reactions between atoms.
Figure 2.11 Electron
orbitals
Energy
Energy: the capacity to do work.
Potential
energy: Energy that can be used for
work.
Stored
energy.
Ex.
ball on the top of a slide
Figure 2.9 Energy
levels of an atoms electrons
Energy in Atoms
Atoms
can store in release energy that is held in their electrons.
Energy
absorbed by an atom causes electrons to move further from the nucleus.
If
energy is released from an atom, the electron falls closer to the nucleus.
The
different state of potential energy that electron have in an atom are called
energy levels, or electron shells.
Atomic Energy Levels (shells)
An
electron can only move to discrete energy levels
and
an atom can only store and release discrete amounts of energy.
Potential Energy in Atoms
Electrons
that are further from the nucleus have greater potential energy.
Electron Configurations and Chemical Properties
The
chemical behavior of an atom is determined by its electron configuration.
The
electron configuration is the distribution of electrons in each of the shells.
The
first shell contains up to two electrons. Subsequent shells contain up to eight
electrons. Shells are filled in order.
The
chemical behavior of an atom depends mostly on the number of electrons in its
outermost shell.
Valence
electrons.
Figure 2.10 Electron
configurations of the first 18 elements
The Periodic Table
92
naturally occurring elements
1
92 protons
Electron
arranged according to protons
Elements
have a periodicity of eight in regard to their chemical properties.
Dmitri
Mendeleev discovered this and developed the periodic table.
The Periodic Table, cont
The
outer shell of electrons are known the valence electrons.
Elements
with 8 electron in the outer level are inert.
Ex.
He, Ne, AR, Kr, Xe, Rn
Those
with unfilled outer shells are reactive.
Ex.
F, Cl, Br, I have 7 in outer shell and are highly reactive.
Forming Molecules
Molecule: a group of 2 more more atoms held together in
a stable association.
Has
particular chemical properties.
Ex.
O2, C6H12O6.
Types of chemical bonds that form molecules:
Ionic
Bonds
Covalent
Bonds
Covalent Bonds
Very
strong form stable molecules.
Form
when two atoms share one or more pairs of valence electrons.
Ex.
H2.
Figure 2.12 Covalent
bonding in four molecules
Why are Covalent Bonds Stable?
No
net charge
Octet
rule is satisfied
No
free electrons
Types of Covalent Bonds
Number
of shared electron pairs
Single
bond share 1 electron pair.
Double
bonds share 2 electron pairs.
Triple
bonds share 3 electron pairs.
Non-polar
and Polar Covalent bonds
Polar Covalent Bonds
Non-polar covalent bond involve
equal sharing of electrons.
Bonds between carbon atoms, and
between carbon and hydrogen are non-polar covalent bonds.
Polar Covalent bonds involve sharing
electrons between an atom with a high degree of electronegativity, such as
oxygen or nitrogen, and hydrogen.
An electronegative atom pulls
electrons toward itself.
Electrons are not equally shared.
The is a partial distribution of
charge.
Figure 2.12x Methane
Figure 2.13 Polar
covalent bonds in a water molecule
Ions and Ionic Bonds
Ion
An
atom that has gain or lost an electron
Has
a net charge
Ex,
Na +, Cl -
An
ionic compound forms by the electrostatic attraction of oppositely charge ions,
ex. NaCl.
Figure 2.14 Electron
transfer and ionic bonding
Figure 2.15 A sodium
chloride crystal
Ionic Bonds in Biology
Ionic
bonds in solids are very strong and form crystals.
Ex.
NaCl crystals
The
cell is an aqueous environment. Ions
dissociate and form weak attractions.
Ex.
Na+ and Cl - ions.
These
weaker attractions are very important in cell biology.
Weak Chemical Bonds play important roles in the chemistry of
life.
When
two molecule make contact, they may temporarily adhere.
Cell
signaling
Turning
on genes
These
weaker attractions are very important in cell biology.
Hydrogen Bonding
A hydrogen atom covalently bonded to one
electronegative atom is also attracted to another electronegative atom.
Figure 2.16 A
hydrogen bond
Chemical Formulae
Structural
formulas
One
line represents a shared pair of electrons:
H-H;
0=0
Molecular
formulas
The
number of each type of atom is indicated in subscript;
H2; O2; C6H12O6.
Shape
A
molecule has a characteristic size and shape.
The
precise shape of a molecule is usually very important to its function in the
cell.
Figure 2.18 Molecular
shape and brain chemistry
Figure 2.19 A
molecular mimic
Chemical Reactions
The
formation and breaking of chemical bonds to rearrange atoms into different
types of molecules.
Reactants
→ Products
A-B
+ C-D → A-C + B + D
Unnumbered Figure (Page 38)
Chemical reaction between hydrogen and oxygen
Figure 2.20
Photosynthesis: a solar-powered rearrangement of matter
Factors Influencing Chemical Reactions
Temperature
Concentration of reactants and
products
Catalysts
The End