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Introduction to Chemistry & Properties of Matter
Transcript of Introduction to Chemistry & Properties of Matter
Matter - anything that has mass and occupies space.
What are the areas of chemistry?
Organic- study of all chemicals containing carbon
2.1 Classifying Matter
Pure vs. Applied Chemistry
Pure Chemistry - pursuit of chemical knowledge for its own sake
*chemists do not expect there to be any immediate practical use of knowledge
Why Study Chemistry
Chemistry can be useful in explaining the natural world, preparing people for career opportunities & producing informed citizens
Chemistry & Materials
Key role in the production of new materials to fit specific needs
Medicine & Biotechnology
Chemistry supplies the medicines, materials and technology that doctors use to treat their patients
Introduction to Chemistry
Properties of Matter
What is Chemistry?
Chemistry- the study of the composition of matter and the changes that matter undergoes
What kind of changes are we talking about?
Because living and nonliving things are made of matter, chemistry effects all aspects of life
Inorganic - study of chemicals that, in general, do not contain carbon. (mainly in non-living things)
Biochemistry - study of the processes that take place in all organisms (digestion, muscle contraction)
Analytical - focuses on the composition of matter (measuring lead in drinking water)
Physical- area of study that deals with the mechanism, the rate, and the energy transfer that occurs when matter undergoes a change
Applied-research that is directed toward a practical goal or application
In practice applied and pure chemistry are linked
*Can help you understand how things work
why does water expand when it freezes
why does sugar dissolve in hot water
Can help you prepare for a career
firefighters need to know which chemical to use
reporters may be asked to interview a chemist to gather background information on a story
Be an informed citizen
industry, private foundations and federal government all provide funds for scientific research
Wouldn't you want to understand and have a say regarding where you money is going?
Should we spend more money on space research or cancer research?
knowledge of chemistry can help you evaluate the data given so you can be an informed voter.
velcro used as a fastener
plant fibers used to create soft cloth
Essential in finding new ways to conserve energy, produce energy & store energy.
marcellus shale ` whats in there?
production of biodiesel from soybeans to be used as fuel
XL pipeline... what is it?
chemist knowledge of the structure and function of chemicals in your cells helps them design safe and effective drugs
probiotics for plants too!
chemistry can supply materials to repair or replace body parts such as skin, arteries and joints
chemists are working on many projects to alter DNA to cure diseases like diabetes and cancer
Chemistry & Agriculture
Chemistry helps to develop more productive crops and safer, more effective ways to protect crops.
testing of soil to see if it contains the right chemicals and recommend ways to improve it
develop plants that are more likely to survive a drought
inserting a gene of a jellyfish into a potato plant. glows when it needs watered
design chemicals to treat specific insect pests only and not the useful insects
Chemistry and the Environment
Chemists help to identify pollutants and prevent pollution, an unintended consequence of new technologies.
lead paint studies showed that the level of lead that is harmful to humans is much lower than had been thought, especially for children.
testing of children's blood for lead
Chemistry and the Universe
to study the universe, chemists gather data from afar and analyze matter that is brought back to Earth
study the composition of stars by analyzing the light they transmit to Earth
discovery of a gas on the sun's surface that was not known on Earth. It was named helium.
analyzed more than 850pounds of moon rocks brought back to Earth, suggesting that vast oceans of molten lava once covered the moon's surface.
space vehicles analyze the chemical composition of rocks & soil on mars, indicating that it was once drenched with water.
The word Chemistry comes from Alchemy
Alchemy was practiced in China & India as early as 400 BC
Had a practical side and mythical side
Alchemists developed the tools & techniques for working with chemicals.
Practical alchemy focused on concepts like perfection
developed processes for separating mixtures and purifying chemicals
designing equipment that is still used today
2.2 Physical Properties
What are some examples of physical properties?
2.3 Chemical Properties
Ch 2. Properties of Matter
Each piece of your clothing has a label that recommends cleaning methods. A 100%-cotton shirt may need to be ironed after washing. A cotton and polyester blend fabric may come out of the dryer wrinkle free. There is no cleaning process that works for all materials.
Why are elements and compounds classified as pure substances?
A pure substance is matter that always has exactly the same composition.
• Table salt and sugar are two examples of pure substances.
Substances can be classified into two categories—elements and compounds
Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.
2.1 Pure substances
* How do mixtures differ from pure substances?
B. Examples of Elements
• Some elements are solids at room temperature. Most soft drink cans are made from aluminum. Carbon is the main element in the marks you make with a pencil.
• The elements oxygen and nitrogen are the main gases in the air you breathe.
• Two elements are liquids at room temperature–bromine and mercury.
C. Symbols for Elements
Chemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is a second letter, it is not capitalized.
• C represents carbon.
• Al represents aluminum.
• Au represents gold. (The Latin name for gold is aurum.)
Symbols allow scientists who speak different languages to communicate without confusion.
For example, nitrogen is azote in France, stickstoff in Germany, and nitrógeno in Mexico.
But all scientists use N as the symbol for the element nitrogen.
Aluminum, carbon, and gold are elements that you can see in common objects, such as cans, pencils, and rings.
Mixtures containing iodine are used to prevent and treat infections.
• A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances.
A compound always contains two or more elements joined in a fixed proportion.
The properties of a compound differ from those of the substances from which it is made.
• Water is composed of the elements hydrogen and oxygen.
Oxygen and hydrogen are gases at room temperature, but water is a liquid.
• Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.
• Silicon dioxide is a compound found in most light-colored grains of sand and in crystals of quartz. It is a colorless, transparent solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a gray solid (silicon). In silicon dioxide, there are always two oxygen atoms for each silicon atom.
How do mixtures differ from pure substances?
• If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a mixture.
Each batch may be slightly different.
The properties of a mixture can vary because the composition of a mixture is not fixed.
• Mixtures can retain some of the properties of their individual substances.
• The properties of a mixture are less constant than the properties of a substance.
Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.
F. Heterogeneous Mixtures
• In a heterogeneous mixture, the parts of the mixture are noticeably different from one another
G. Homogeneous Mixtures
• In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.
• Sand is a heterogeneous mixture of different kinds of grains. The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel.
1. Which of these substances is a compound?
2. Which of these groups of letters could be used as a symbol for an element?
3. Which of the following statements does not apply to a compound?
a. It is made of two or more elements.
b. It has components that are joined in fixed proportions.
c. It can be separated into components by physical methods.
d. It can be broken down into elements or other compounds.
4. How does a compound differ from a mixture?
a. A compound cannot be broken down into simpler substances.
b. Compounds can be separated by physical processes and mixtures cannot.
c. The composition of a mixture cannot vary.
d. A compound is made of two or more elements in fixed proportion
5. Which of these materials is a heterogeneous mixture?
6. Which of the following can be separated with a filter?
Making Sodium Chloride (NaCl)
Sodium in water
H. Solutions, Suspensions and Colloids
What is the main difference among solutions, suspensions, and colloids?
• The size of the particles in a mixture has an effect on the properties of the mixture
Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.
When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution.
A suspension is a heterogeneous mixture that separates into layers over time.
A colloid contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension.
• Like solutions, colloids do not separate into layers.
• You cannot use a filter to separate the parts of a colloid.
These liquids represent three categories of mixtures.
• Windshield wiper fluid is a solution.
• Muddy water collected from a swamp is a suspension.
• Milk is a colloid.
Milk is a colloid -
what is homogenized milk?
There are pitchers of ice water and lemonade on a picnic table. How do you know which liquid is in each pitcher? It’s easy! Lemonade is yellow and has a tart taste that is hard to miss. A yellow color and a tart taste are two properties of lemonade
A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material.
Viscosity, conductivity, malleability, hardness, melting point, boiling point, and density are examples of physical properties.
The tendency of a liquid to
flowing is called its viscosity.
• Thick liquids, such as corn syrup and honey, have a
• Thin liquids, such as vinegar and water, have a
A material’s ability to allow heat to flow is called conductivity.
• Materials that have a high conductivity, such as metals, are called conductors.
• Good conductors of heat are usually also good conductors of electricity.
The ability of a solid to be hammered without shattering is malleability.
• Most metals, such as gold, are malleable.
• An ice cube or piece of glass breaks into small pieces when struck with a hammer. Solids that shatter when struck are brittle, not malleable.
One material can scratch another material if it is harder than the other material.
• A kitchen knife can scratch a copper sheet because stainless steel is harder than copper.
• The material used to sharpen the knife blade must be harder than stainless steel.
Diamond is the hardest known material.
E. Melting and Boiling Points
The temperature at which a material changes state is a physical property.
• The temperature at which a substance changes from solid to liquid (melts) is its melting point.
• The temperature at which a substance changes from liquid to gas (boils) is its boiling point
Which of these substances are liquids at room temperature (20°C, or 68°F)?
The ratio of the mass of a substance to its volume is its density.
• Density can be used to test the purity of a substance.
• Silver has a density of 10.5 g/cm3. A coin with a density of 9.9 g/cm3 is not made from silver, or it contains substances in addition to silver.
G. Using Properties to Identify Materials
How can knowing the physical properties of matter be useful?
Physical properties are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture.
A material can be identified by its properties.
• Decide which properties to test.
• Do tests on a sample of the unknown material.
• Compare the results with the data reported for known materials.
• Properties determine which materials are chosen for which uses.
For example, shoelaces must be flexible, that is they must be able to bend without breaking.
They must also be durable, that is, they must be able to withstand repeated use.
H. Using Properties to Separate Mixtures
What processes are used to separate mixtures?
Filtration and distillation are two common separation methods.
• You can separate hot tea from loose tea leaves by pouring the mixture through a strainer. Filtration is a process that separates materials based on the size of their particles
• People filter (sift) dirt through a wire screen to locate small objects. Particles of dirt are small enough to pass through the holes, but objects such as broken bits of pottery are too large.
• Sometimes all the particles in a solution are small enough to pass through a filter. Distillation is a process that separates the substances in a solution based on their boiling points.
K. Recognizing Physical Changes
• The change of water from a liquid to a gas during boiling is a physical change. A physical change occurs when some of the properties of a material change, but the substances in the material remain the same.
During a physical change, the size and shape of a material can change but not the composition. Some examples include
• melting butter in a pan
• crumpling a piece of paper
• slicing a tomato
Some but not all physical changes can be reversed. Braiding hair is a reversible change. Cutting hair cannot be reversed.
1. Which of the following is not a physical property?
b. boiling point
2. Which of these materials is not malleable?
3. In choosing a material for use as a wire to carry electric current, which physical property would be most important?
d. boiling point
4. Which of these statements best describes a physical change in a pure substance?
a. The substance changes into one or more new substances.
b. Some of the properties of the substance change, but the material remains the same.
c. The properties of the material do not change, and the material remains the same.
d. The substance is separated into two or more simpler substances.
5. The process of filtration uses the difference in boiling points of substances to separate a mixture.
How would you describe candles? Color, hardness, and density are physical properties that you can use in the description. You can also say that the candles are burning. The ability to burn is not a physical property. As a candle burns, new substances form.
Observing Chemical Properties
When can chemical properties be observed
As a candle burns, its compounds combine with oxygen in the air to form water and carbon dioxide.
A chemical property is any ability to produce a change in the composition of matter. Flammability and reactivity are two examples of chemical properties
Chemical properties can be observed only when the substances in a sample of matter are changing into different substances
• Materials that burn can be used as fuel. Flammability is a material’s ability to burn in the presence of oxygen
• The property that describes how readily a substance combines chemically with other substances is reactivity.
• Rust forms when oxygen reacts with iron and water. Rust is a brittle, reddish-brown compound. Because iron is highly reactive, you would not choose iron to make jewelry or coins
What observations might indicate that a chemical change has occurred?
Three common types of evidence for a chemical change are
1. a change in color
2. the production of a gas
3. the formation of a precipitate.
C. A Change in Color
A change in color is a clue that a chemical change has produced at least one new substance.
• A shiny silver bracelet that is exposed to air will darken.
• As a match burns, it shrivels up and turns black.
• A new copper roof and an old copper roof have different colors
• A new copper roof has a reddish color.
The green patina on an old copper roof is a mixture of copper compounds.
D. Production of a Gas
When you mix vinegar with baking soda, bubbles of carbon dioxide form immediately. A similar chemical change happens when you use baking powder as an ingredient in a cake recipe. Bubble of carbon dioxide expand and cause the cake to rise.
E. Formation of a Precipitate
Any solid that forms and separates from a liquid mixture is called a precipitate.
When an acid is added to milk, proteins in the milk undergo a chemical change that causes them to stick together in clumps and form a precipitate–cottage cheese.
Is a Change Chemical or Physical?
What is the difference between chemical and physical changes?
Are different substances present after a change takes place? If not, then the change is physical, not chemical
When matter undergoes a chemical change, the composition of the matter changes.
Even if you observe a color change, a gas, or a precipitate, you cannot be sure that a chemical change has taken place. When an iron horseshoe is heated, its color changes from gray to red, but the iron is still iron. That means the change is physical, not chemical.
1. Which of these properties is a chemical property of sulfur?
2. Which of the following is not a common type of evidence for a chemical change?
a. a change of state
b. a color change
c. a gas produced
d. a precipitate formed
3. You can be certain that a chemical change has occurred when
a. there is a visible change.
b. the change is irreversible.
c. the temperature changes.
d. a new substance is formed.
the medieval forerunner of chemistry, based on the supposed transformation of matter. It was concerned particularly with attempts to convert base metals into gold or to find a universal elixir
* An element has a fixed composition because it contains only one type of atom.
No two elements contain the same type of atom.
An element is a substance that cannot be broken down into simpler substances.
• Nitrogen has many uses that depend on its low reactivity.
• Researchers in Japan pump nitrogen gas into the steel tanks that hold seawater in ships. The nitrogen displaces the oxygen dissolved in the water and prevents rusting
The color change in a banana peel is caused by chemical changes that are taking place in the cells of the banana. A chemical change occurs when a substance reacts and forms one or more new substances