Transcript Covalent Bonds

Science, Systems, Matter, and Energy
G. Tyler Miller’s
Living in the Environment
13th Edition
Chapter 3
Key Concepts
Science as a process for understanding
Components and regulation of systems
Matter: forms, quality, and how it
changes; laws of matter
Energy: forms, quality, and how it
changes; laws of energy
Nuclear changes and radioactivity
Frontier Science vs
Consensus Science
• News reports focus on:
– New so-called scientific breakthroughs
– Disputes between scientists over the validity of untested
data
• These preliminary results are called frontier science. They are
controversial because they haven’t been tested or accepted.
Remember, it’s healthy for scientists to disagree
• Consensus science consists of data, theories, and laws that
scientists who are considered to be experts in the field
involved widely accept
• This aspect of science is very reliable, but not considered to be
newsworthy
Models and Behavior of Systems
A system is a set of components that: 1) function and
interact in some regular and predictable manner, 2) can be
isolated for the purposes of study
A system has the following components:
 Inputs- things that flow into the system such as energy
or matter
 Flows (throughputs)-matter or energy within the system
at certain rates
 Stores (storage areas)- where matter or energy can
accumulate before being released
 Outputs- matter or energy that flows out of a system and
sinks into the environment
System Regulation (Feedback Loops)
 Positive Feedback
 Homeostasis
 Negative Feedback
 Time Delay
 Synergy
Fig. 3-3 p. 46
Matter: Forms, Structure, and Quality
Elements
Compounds
Molecules
Mixtures
Elements
• Elements are substances that cannot be broken down into
simpler substances by ordinary chemical reactions
– chemical symbols: usually the first or first and second letter of the
English or Latin name
• oxygen- O
• sodium- Na
• 92 naturally occurring elements ranging from hydrogen to
uranium
• Four elements (C, H, O, N) are responsible for over 96% of
the mass of most organisms
• Trace elements are those that are present, but in small
amounts; equally necessary for organisms to function
– e.g. iodine and copper
Atoms
• Atoms are the fundamental particles of elements
• In order to be seen with the visible eye, the most advanced
microscopes are magnified as high as 5 million times
• Smallest component of an element that retains the chemical
properties of an element
– protons: carry a unit of positive charge
– electrons: carry a unit of negative charge
– neutron: uncharged particle
• An electrically neutral atom contains the same number of
electrons and protons
• Protons and neutrons cluster together to form the atomic
nucleus while electrons occupy empty spaces surrounding the
nucleus
• How do we identify atoms?
– An atom in uniquely identified by its number of
protons, the atomic number
• The periodic table depicts the elements in
order of their atomic number
• The atomic number determines an atom’s
identity and defines the element
• Atomic numbers are denoted in subscript to
the left of the chemical symbol
1
H = 1 proton
26
Fe = 26 protons
• The mass of an atom is very small and cannot be expressed in
grams or micrograms
• Such masses are expressed in terms of the atomic mass unit
(amu) o
• The mass of an atom is referred to atomic mass and is
indicated by the number of protons added to the number of
neutrons
• The atomic mass indicates approximately how much matter it
contains as compared with another atom
• Atomic mass number is denoted by a superscript to the left of
the chemical symbol
atomic mass
16
8
atomic number
o
Electron Orbitals
• Electrons move through regions 3-D space around the
nucleus, called orbitals
• Each orbital contains different energy levels
– electrons most distant from the nucleus have more energy
because less energy is required for attraction to a positive
charge
• Valence electrons are those that contain the most
energy
– occupy valence shells
• Electrons can move between orbitals as long as
certain energy requirements are met
Isotopes
• Most elements consist of a mixture of atoms
with different numbers of neutrons, thus
having different masses
• Isotopes of the same element have the same
number of protons and electrons; only the
number of neutrons vary
12
14
– e.g. C and
C
6
6
Chemical Bonds
Chemical formulas
Ionic bonds
Covalent bonds
Hydrogen bonds
Chemical Reactions
• Atoms of different elements combine to form
chemical compounds
– atoms must be in fixed ratio
• H2O: 2 atoms hydrogen to 1 atom oxygen
• Two or more atoms can become very strongly
joined to form a molecule
– molecules are created by covalent bonds only
• O2 or N2 not NaCl
Chemical Bonds
• Forces of attraction that hold atoms of a compound
together
• Energy required to break chemical bonds is the bond
energy
• Three types of bonds differing by the mechanism in
which they form and their relative bond strength:
– covalent bonds
– ionic bonds
– hydrogen bonds
Covalent Bonds
• Covalent bonds share electrons in such a way that
each atom has a full valence shell
– refer specifically to bonding of non-metals
• Atoms tend to be reactive if the valence shell is not
full
• Lewis structures are simple ways of representing the
electrons in the valence shell of an atom and how
they are shared
e.g. methane, CH4
carbon has 4 valence electrons all
available for covalent bonding
C
hydrogen has 1 valence electron
available for covalent bonding
H
H
H
H
methane, CH4
H
C
methane, CH4
H
H
C
methane, CH4
H
H
C
H
methane, CH4
H
H
C
H
H
Special Covalent Bonds
• Atoms of different elements vary in their affinity for
electrons
• Electronegativity is the measure of an atom’s
attraction for electrons that are shared
• When covalently bonded atoms have similar
electronegativities, the electrons are shared equally.
This state is described as nonpolar
• If the electronegativities are different, the electrons
are pulled closer to the atom with the greater electron
affinity. This results in a polar covalent bond
– has 2 dissimilar ends, or poles, one partially positive and
one partially negative
Ionic Bonds
• Some atoms are not electrically neutral and will have
more or less charge than another
• A particle with one or more units of electrical charge
is an ion which is formed by the addition or loss of 1
or more electrons
– cations: a positively charged atom that has lost 1 or more
electron from it’s valence shell
– anions: a negatively charged atom that has gained 1 or
more electron
• Ionic bonds result from the attraction of a cation to an
anion
Ionic bonding
Na has 1
valence
electron and
acts as a
donor
Cl has 7
valence
electrons and
acts as an
acceptor
• Compounds joined by
ionic bonds tend to
dissociate in water
• Water acts as a solvent
and dissovles many
substances that are polar
or ionic
• NaCl, or any dissolved
substance is referred to
as a solute
hydration
Hydrogen Bonds
• Hydrogen bonds are weak attractions
involving partially charged hydrogen atoms
• In a water molecule hydrogen is partially
positively charged because the electron spends
more time closer to the electronegative oxygen
atom
• Individually, hydrogen bonds are weak, but are
collectively strong in large numbers
– e.g. DNA
Organic Compounds
 Organic vs. inorganic compounds: Organic
compounds are those that contain carbon
combined with another element
 Hydrocarbons- compounds of carbon and
hydrogen, methane, for example
 Chlorinated hydrocarbons-compounds
of carbon, hydrogen, and chlorine, DDT for
example
Organic Compounds
 Chlorofluorocarbons- compounds containing carbon,
chlorine, and fluorine, Freon-12 for example
Simple carbohydrates- certain compounds of carbon,
hydrogen, and oxygen, glucose for example---C6H12O6
 Complex carbohydrates- consist of two or more simple
carbohydrates linked together
Genetic Material
Nucleic acids
Genes
Chromosomes
Gene mutations
Fig. 3-6 p. 50
The Four States of Matter
Solid
Liquid
Gas
Fig. 3-7 p. 50
Energy: Forms
Kinetic energy Potential energy
Heat
Fig. 3-9 p. 52
The Law of Conservation of Matter
Matter is not consumed
Matter only changes form
There is no “away”
Matter and Pollution: How severe are
pollutants?
 Chemical nature of pollutants
 Concentration
 Persistence
 Degradable (nonpersistent) pollutants: have broken down
completely or reduced to acceptable levels
 Biodegradable pollutants- complex chemical pollutants that
living organisms break down
 Slowly degradable (persistent) pollutants-take decades to
degrade
 Nondegradable pollutants- cannot be broken down by
natural processes
Nuclear Changes: nuclei of isotopes
change into a different isotope
Natural radioactive decay
Radioactive isotopes (radioisotopes)
Gamma rays
Alpha particles
Beta particles
Half life (See Table 3-2 p. 56)
Fig. 3-13 p. 56
Ionizing radiation
Nuclear Reactions
Fission
Fig. 3-16 p. 57
Fusion
Fig. 3-17 p. 58
Effects of atomic bomb at Hiroshima
Laws Governing Energy Changes
First Law of Thermodynamics (Energy)
 Energy is neither created nor destroyed
 Energy only changes form
 You can’t get something for nothing
ENERGY IN = ENERGY OUT
Laws Governing Energy Changes
Second Law of Thermodynamics
 In every transformation, some energy is
converted to heat
 You cannot break even in terms of
energy quality