A. Chapter 2: Science, Matter, Energy, and Systems

AP Environmental Science Review

2-1: What do Scientist Do?
Science – an attempt to discover how nature works and use that knowledge to describe what is likely to happen in nature.
Scientific Method:
Identify a Problem
Find out what is known about the problem
Ask a question to investigate
Perform and experiment and collect and analyze data to answer the question
Propose a hypothesis to explain the data
A possible and testable answer to a scientific question or explanation of what scientist observe in nature
Use the hypothesis to make projections that can be tested
Test the projections with further experiments or observations
Model – an approximate representation or simulation of a system
Accept or revise the hypothesis
Scientific Theory – a well-tested and widely accepted scientific hypothesis or a group of related hypothesis
Four important features of the scientific process are curiosity, skepticism, reproducibility, and peer review
Thinking critically involves:
Be skeptical about everything you read or hear
Look at the evidence and evalutate it
Be open to many viewpoints
Identify and evaluate your personal assumptions, biases, and beliefs
Scientific Law (Law of Nature) – a well-tested and widely accepted description of what we find happening repeatedly and in the same way in nature.
Example: Law of gravity
We CANNOT break a scientific law
Tentative Science (Frontier Science) - Preliminary scientific results that capture news headlines have not been widely tested and accepted by peer review.
Reliable Science – consists of data, hypothesis, models, theories, and laws that are widely accepted by all or most of the scientist who are considered experts in the field under study.
Unreliable Science - scientific hypothesis and results that are presented as reliable without having undergone the rigors of widespread peer review, or that have been discarded as a result of peer review.
Science has 4 important limitations:
Scientist cannot prove or disprove anything absolutely instead they try to establish a theory or law that has a high probability or certainty of being useful
Scientist are human and thus are not totally free of bias about their own results and hypothesis
Many systems in the natural world involve a huge number of variables with complex interactions
The use of statistical tools
Example: No way to measure accurately how many metric tons of soil are eroded annually worldwide

2-2: What is Matter and What Happens When It Undergoes Change?
Matter – anything that has mass and takes up space
Exists in three physical states: Solid, Liquid, Gas
Two chemical forms: Elements and Compounds
Element – a fundamental type of matter that has a unique set of properties and cannot be broken down into simpler substances by chemical means.
Compounds –combinations of tow or more different elements held together in fixed proportions
Atom – the most basic building block of matter
The idea that all elements are made up of atoms is called the atomic theory
3 subatomic particles:
Neutrons (n) – no electrical charge
Protons (p) – has a positive charge (+)
Electrons (e) – has a negative charge (-)
Extremely small center called the nucleus
Electron Probability Cloud – we do not know the exact locations, but the cloud represents an area in which there is a high probability of finding them
An atom in its basic form has no net electrical charge
Atomic Number – equal to the number of protons in the nucleus of its atom
Mass Number – the total number of neutrons and protons in its nucleus
Most of the atom’s mass is concentrated in its nucleus
Isotopes - Forms of an element having the same atomic number but different mass numbers
Molecule – a combination of two or more atoms of the same or different elements held together by forces called chemical bonds (Ex. H2O)
Ion – an atom or a group of atoms with one or more net positive or negative electrical charges (Ex. NO3-)
Important for measuring a substance’s acidity in a water solution.
A chemical characteristic that helps determine how a substance dissolved in water will interact with and affect its environment
Hydrogen (H+) and Hydroxide (OH-)
pH is a measure of acidity
Neutral Solution – has a pH of 7
Acidic Solution – has a pH less than 7
Basic Solution – has a pH greater than 7
Chemical Formula – is written to show the number of each type of atom or ion in a compound.
Organic Compounds – because they contain at least two carbon atoms
Methane (CH4) – has only one carbon atom but is considered an organic compound
Hydrocarbons – compounds of carbon and hydrogen
Chlorinated Hydrocarbons – compounds of carbon, hydrogen, and chlorine
Simple Carbohydrates (simple sugars) – certain types of compounds of carbon, hydrogen, and oxygen atoms
Large and more complex organic compounds, essential to life, are composed of macromolecules
Some of these are called polymers – formed when a number of simple organic molecules (monomers) are linked together by chemical bonds
Complex Carbohydrates – cellulose and starch
Proteins – amino acids
Nucleic Acids – nucleotides
Lipids – fats, waxes, that are not made of monomers but are a fourth type of macromolecule essential for life
Inorganic Compounds – all other compounds without the carbon bond
Cells – the fundamental structural and functional units of life
Cell Theory - The idea that all living things are composed of cells
Genes – contains instructions, or codes, called genetic information, for making specific proteins
Trait – or characteristic, passed on from parents to offspring during reproduction in an animal or plant
Chromosome – thousands of genes make up a single chromosome
Physical Change – when there is no change in the chemical composition
Chemical Change (Chemical Reaction) – there is a change in the chemical composition of the substances involved.
Matter can undergo three types of change or nuclear change – change in the nuclei of its atom
Radioactive Decay: spontaneously emit fast-moving chunks of matter
Nuclear Fission – occurs when the nuclei split apart
Nuclear Fusion – two nuclei are forced together
Law of Conservation of Matter: whenever matter undergoes a physical or chemical change, no atoms are created or destroyed.
We can change elements and compounds from one physical or chemical form to another, but we cannot create or destroy any of the atoms involved in any physical or chemical change.
2-3: What is Energy and What Happens When it Undergoes Change?
Work – done when any object is moved to a certain distance
Work = Force X Distance
Energy – the capacity to do work or to transfer heat
Kinetic Energy – matter in motion
Heat/Thermal Energy – a form of kinetic energy, the total kinetic energy of all moving atoms, ions, or molecules of an object
Molecules move faster, it will become warmer
Heat flows from the warmer object to the cooler object
Electromagnetic radiation – a form of kinetic energy, many different forms of electromagnetic radiation, each form having a different wavelength and energy content
Potential Energy – stored and potentially available for use
We can change potential to kinetic
Divide energy resources into 2 categories:
Renewable Resources – energy gained from resources that are replenished by natural processes in a relatively short time
Indirect forms of renewable solar energy:
Wind, Hydropower, Biomass
Nonrenewable Resources – energy from resources that can be depleted and are not replenished by natural processes within a human time scale.
Fossil Fuels – oil, coal, and natural gas
Commercial Energy – energy that is sold in the marketplace
Energy Quality – a measure of the capacity of a type of energy to do useful work
High Quality Energy – concentrated energy that has a high capacity to do useful work
Low Quality Energy – energy that is so dispersed that it has little capacity to do useful work
Laws of Thermodynamics:
1st Law of Thermodynamics – Law of Conservation of Energy – whenever energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed.
2nd Law of Thermodynamics – whenever energy is converted from one form to another in a physical or chemical change, we end up with lower-quality or less useable energy than we started with – usually this loss takes the form of heat that flows into the environment
To improve our energy efficiency – which means getting more work out of the energy we use – we need to stop wasting ½ the energy we use
2-4: What are Systems and How Do They Respond to Change?
System – a set of components that function and interact in some regular way
Inputs – matter and energy from the environment
Flows/Throughputs – matter and energy within the system
Outputs – matter and energy to the environment
Feedback – any process that increases (positive feedback) or decreases (negative feedback) a change to a system
Feedback Loop – occurs when an output of matter, energy, or information is fed back into the system as an input and leads to changes in that system
Positive Feedback Loop – causes a system to change further in the same direction
Example: the melting of the polar ice caps
Negative/Corrective Feedback Loops – causes a system to change in the opposite direction from which it is moving
Example: A thermostat or recycling and reuse
Time Delay – or lack of response during a period of time between the input of a feedback stimulus and the system’s response to it
Can allow an environmental problem to build up slowly until it reaches a threshold level (tipping point – the point at which a fundamental shift in the behavior of a system occurs)
Prolonged Delays – dampen the negative feedback mechanisms that might slow, prevent, or halt environmental problems
Synergistic Interaction (Synergy) – can be positive or negative, occurs when two or more processes interact so that the combined effect is greater than the sum of their separate effects