Topic 1 Topic 1 Topic 1 Topic 1 Topic 1: Chemistry and Matter Table of Contents Basic Concepts...

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Topic 1Topic 1 Topic 1: Chemistry and Matter

Table of ContentsTable of Contents

Basic Concepts

Additional Concepts

• Chemistry is the science that investigates and explains the structure and properties of matter.

Composition, Structure, and Behavior

Chemistry and Matter: Basic ConceptsChemistry and Matter: Basic Concepts Chemistry and Matter: Basic ConceptsChemistry and Matter: Basic Concepts

• Matter is the stuff that’s all around you: the metal and plastic of a telephone, the paper and ink of a book, the glass and liquid of a bottle of soda, the air you breathe, and the materials that make up your body.

• A more formal definition of matter is anything that takes up space and has mass.

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• Mass is the measure of the amount of matter that an object contains.

Composition, Structure, and Behavior

• The structure of matter refers to its composition—what matter is made of—as well as how matter is organized.

• The properties of matter describe the characteristics and behavior of matter, including the changes that matter undergoes.

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• Matter that is large enough to be seen is called macroscopic, so all of your observations in chemistry, and everywhere else, start from this perspective.

Macroscopic View of Matter

• You may get hints of the actual structure from a macroscopic view. You must go to a submicroscopic perspective to understand how the hidden structure of matter influences its behavior.

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• The submicroscopic view gives you a glimpse into the world of atoms.

Submicroscopic View of Matter

• It is a world so small that you cannot see it even with the most powerful microscope, hence the term submicroscopic.

• You learned in earlier science courses that matter is made up of atoms.

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• In your study of chemistry, you will use both macroscopic and submicroscopic perspectives.

Using Models in Chemistry

• For example, sucrose and aspirin are both composed of carbon, hydrogen, and oxygen atoms, but they have different behaviors and functions.

• These differences must come about because of differences in the submicroscopic arrangement of their atoms.

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aspirin sucrose

Comparing the Structures of Aspirin and Sucrose

• The different submicroscopic arrangements of the atoms in aspirin and sucrose cause the differences in their behavior.

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Using Models in Chemistry Topic 1Topic 1


• A scientific model is a thinking device that helps you understand and explain macroscopic observations. Scientific models are built on experimentation.

• A powerful way to classify matter is by its composition. This is the broadest type of classification.

Classification by Composition

• A qualitative observation is one that can be made without measurement.

• When you examine an unknown piece of stuff, you first ask, “What is it made of?”

• Sucrose is composed of the elements carbon, hydrogen, and oxygen. This is a qualitative expression of composition.

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• After a qualitative analysis, the next question that you might ask is how much of each of the elements is present.

Classification by Composition

• A quantitative observation is one that uses measurement.

• For sucrose, the answer to that question is that 100 g of sucrose contains 42.1 g of carbon, 51.4 g of oxygen, and 6.5 g of hydrogen. This is a quantitative expression of composition.

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Pure substance or a mixture? Topic 1Topic 1


• A substance is matter, either an element or compound, with the same fixed composition and properties.

• A sample of matter is either pure—made up ofonly one kind of matter— or it is a mixture of different kinds of matter.

• A mixture is a combination of two or more substances in which the basic identity of eachsubstance is not changed.

• Unlike pure substances, mixtures do not have specific compositions.

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Pure substance or a mixture?

• A physical change is a change in matter that does not involve a change in the chemical identity of individual substances.

• Examples of physical changes include:

• boiling,

• freezing,

• melting,

• evaporating,

• dissolving,

• and crystallizing.

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• Physical properties are characteristics that a sample of matter exhibits without any change in its identity.

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• Examples of the physical properties of a chunk of matter include its:• solubility,• melting point,• boiling point,• color,• density,• electrical conductivity,• and physical state (solid, liquid, or gas).

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• A heterogeneous mixture is one with different compositions, depending upon where you look.

• The components of the mixture exist as distinct regions, often called phases.

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• Homogeneous mixtures are the same throughout.

• Another name for a homogeneous mixture is solution.

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• Some solutions are gases. Air, for example, is a homogeneous mixture of several gases.

• Some solutions are solid.

• Liquid solutions do not have to be liquid or contain water.

• Alloys are solid solutions that contain different metals and sometimes nonmetallic substances.

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• When you dissolve sugar in water, sugar is the solute—the substance being dissolved.

• The substance that dissolves the solute, in this case water, is the solvent.

• When the solvent is water, the solution is called an aqueous solution.

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• Many of the solutions you encounter are aqueous solutions, for example, soda, tea, contact-lens cleaner, and other clear cleaning liquids.

• In addition, most of the processes of life occur in aqueous solutions.

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Two Types of Substances

• One type of pure substance can be broken down into simpler substances. This type of substance is called a compound.

• Another type of substance cannot be broken down into simpler substances. Such a substance is called an element.

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• All the substances of the universe are either elements, compounds formed from elements, or mixtures of elements and compounds.

Two Types of Substances

• Of the known elements, only about 90 occur naturally on Earth. The remainder are synthesized, usually in barely detectable amounts, in high-energy nuclear experiments. • Less than half of the 90 naturally occurring elements are abundant enough to play a significant role in the chemistry of everyday stuff.

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Organizing the Elements

• The periodic table organizes elements in a way that provides a wealth of chemical information—much more than is evident to you now. It shows the chemical symbols for the elements.

• Their symbols usually correspond to their names in Latin.

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Periodic Table of the ElementsTopic 1Topic 1


Compounds Are More Than One Element

• A more complete definition is that a compound is a chemical combination of two or more different elements joined together in a fixed proportion with a unique set of chemical and physical properties.

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• More than 10 million compounds are known and the number keeps growing.

Compounds Are More Than One ElementTopic 1Topic 1


• Some new compounds are discovered and isolated from natural chemical sources such as plants and colonies of bacteria and are synthesized in laboratories for many different uses.


• The properties of the compound are different from the properties of the elements that compose the compound.

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silver + bromine = silver bromide


• More than 10 million compounds are known and the number keeps growing.

• New compounds are discovered and isolated from natural chemical sources such as plants and colonies of bacteria and are synthesized in laboratories for many different uses.

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• A formula is a combination of the chemical symbols that show what elements make up a compound and the number of atoms of each element.

Compound Formula

Caffeine C8H10N4O2

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• Formulas provide a shorthand way of describing a submicroscopic view of a compound.

• You probably already use formulas like H2O and CO2 as a way of talking about water and carbon dioxide.

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States of Matter• Most matter on Earth exists in one of three

physical states: solid, liquid, or gas. A fourth state of matter, called plasma, is less familiar.

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• Changes in state are examples of physical changes because there is no change in the chemical composition identity of the substance.

• Ice can melt back to form liquid water, and steam will condense on a cool surface to form liquid water.

States of Matter

• Some substances are described as volatile, which means that they change to a gas easily at room temperature.

• Alcohol and gasoline are more volatile than water.

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• Density is the amount of matter (mass) contained in a unit of volume.

• Styrofoam has a low density or small mass per unit of volume.

States of Matter

• Stones have a large density or a large mass per unit of volume.

• In science, the density of solids and liquids is usually measured in units of grams (mass) per milliliter (volume) or g/mL.

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Chemical Properties

• Chemical properties are those that can be observed only when there is a change in the composition of the substance.

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• Rusting is a chemical reaction in which iron combines with oxygen to form a new substance, iron oxide.

• Inability to react is also a chemical property.

Chemical Changes

chemical change, the change of one or more substances into other substances.

• A chemical property always relates to a

• Another term for chemical change is chemical reaction.

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Chemical ChangesTopic 1Topic 1


Click box to view movie clip.

Chemical Changes

• All matter is made of atoms, and any chemical change involves only a rearrangement of the atoms. Atoms do not just appear. Atoms do not just disappear.

• This is an example of the law of conservation of mass, which says that in a chemical change, matter is neither created nor destroyed. It would be equally correct to call this the law of conservation of matter.

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Chemical Reactions and Energy

• All chemical changes also involve some sort of energy change.

• Energy is either taken in or given off as the chemical change takes place. Energy is the capacity to do work.

• Work is done whenever something is moved.

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• Many reactions give off energy.

• For example, burning wood is a chemical change in which cellulose, and other substances in the wood, combine with oxygen from the air to produce mainly carbon dioxide and water.

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• Energy is also produced and released in the form of heat and light.

• Chemical reactions that give off heat energy are called exothermic reactions.

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• Chemical reactions that absorb heat energy are called endothermic reactions.


• You can tell that the decomposition of water into oxygen and hydrogen is an endothermic reaction because it doesn’t occur unless energy, in the formof an electric current, is passed through water.

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• Photosynthesis is probably the most important endothermic process on Earth.

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• Green plants, algae, and many kinds of bacteria carry out photosynthesis.

Basic Assessment QuestionsBasic Assessment Questions

Question 1

Identify each of the following as either a compound or a mixture.

A. sand

B. water

C. juice

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Answers

A. sand

B. water

C. juice

mixture

compound

mixture

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Classify each of the following as a chemical or physical property.

Question 2

A. density

B. reactivity

C. color

D. melting point

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Answers

A. density

B. reactivity

C. color

D. melting point

physical property

chemical property

physical property

physical property

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Chemistry and Matter: Additional ConceptsChemistry and Matter: Additional Concepts Chemistry and Matter: Additional ConceptsChemistry and Matter: Additional Concepts Topic 1Topic 1

Additional Concepts

Chemistry and Matter: Additional ConceptsChemistry and Matter: Additional Concepts Chemistry and Matter: Additional ConceptsChemistry and Matter: Additional Concepts

Branches of Chemistry

Branch Area of Emphasis Examples

Organic chemistry

most carbon-containing chemicals pharmaceuticals, plastics

Inorganic chemistry

in general, matter that does not contain carbon

minerals, metals and nonmetals, semi-

conductors

Physical chemistry

the behavior and changes of matter and the related energy changes

reaction rates, reaction mechanisms

Analytical chemistry

components and composition of substances

food nutrients, quality control

Biochemistry matter and processes of living organisms

metabolism, fermentation

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Scientific Methods

• A scientific method is a systematic approach to answer a question or study a situation.

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• It is both an organized way for scientists to doresearch and a way for scientists to verify the work of other scientists.

Scientific Methods

• A typical scientific method includes:

• making observations,

• forming a hypothesis,

• performing an experiment,

• and arriving at a conclusion.

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Scientific Methods

• Often, a scientist will begin with qualitative data—information that describes color, odor, shape, or some other physical characteristic that relates to the five senses.

• Chemists also use numerical quantitative data.

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• A hypothesis is a possible explanation for what has been observed.

• An experiment is a set of controlled observations that test a hypothesis.

Scientific Methods

• The variable that is changed in an experiment is called the independent variable.

• The variable that you watch to see how it changes as a result of your changes to the independent variable is called the dependent variable.

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Scientific Methods

• Many experiments also include a control, which is a standard for comparison.

• A conclusion is a judgment based on the data obtained in the experiment.

• If data support a hypothesis, the hypothesis is tentatively affirmed. Hypotheses are never proven; they are always subject to additional research.

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Scientific Methods

• Over time, data from many experiments can be used to form a visual, verbal, and/or mathematical explanation—called a model—of the phenomenon being studied.

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• A theory is an explanation that has been supported by many experiments.

• Theories are always subject to new experimental data and are modified to include new data.

Scientific Methods

• A scientific law describes a relationship in nature that is supported by many experiments and for which no exception has been found.

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Scientific Research

• Pure research is done to gain knowledge for the sake of knowledge itself.

• Applied research is undertaken to solve a specific problem.

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Additional Assessment QuestionsAdditional Assessment Questions

Identify the dependent variable and the independent variable in the following experiments.

Question 1 Topic 1Topic 1

A student tests the ability of a given chemical to dissolve in water at three different temperatures.

independent variable: temperature; dependent variable: ability to dissolve in water

Answer 1a

Question 1a Topic 1Topic 1


A farmer compares how his crops grow with and without phosphorous fertilizers.

independent variable: presence of phosphorous fertilizer; dependent variable: crop growth

Answer 1b

Question 1b Topic 1Topic 1


Classify each kind of research as either pure or applied.

Question 2Topic 1Topic 1


A scientist studies plants in a rain forest in search of chemicals that might be used to treat AIDS.

applied

Answer 2a

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A researcher studies the effects of hormones on the brain of a worm.

pure

Answer 2b

Question 2b Topic 1Topic 1


A researcher tries to develop cleaner burning fuels to help reduce air pollution.

applied

Answer 2c

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