chemistry is the science that investigates and explains the structure and properties of matter

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

Chemistry and Matter

*Matter –

*Anything that has mass and takes up space

* Matter is the stuff that’s all around you

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

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

What’s the difference between mass & weight?

What's the difference between weight and mass?

As long as you stay on Earth, the difference is more philosophical than practical. Uh...what do you mean by that?

Well, mass is a measurement of how much matter is in an object; weight is a measurement of how hard gravity is pulling on that object. Your mass is the same wherever you are--on Earth, on the moon, floating in space--because the amount of stuff you're made of doesn't change. But your weight depends on how much gravity is acting on you at the moment; you'd weigh less on the moon than on Earth, and in interstellar space you'd weigh almost nothing at all.

But if you stay on Earth, gravity is always the same, so it really doesn't matter whether you talk about weight or mass. That's right...but scientists still like to be careful about distinguishing between the two. If you talk about the mass of an atom--as I will do from now on--you're always talking about the same thing; if you talk about its weight, what you mean depends on where the atom is.

Mass is a measurement of how much matter is in an object; weight is a measurement of how hard gravity is pulling on that object.

Your mass is the same wherever you are--on Earth, on the moon, floating in space--because the amount of stuff you're made of doesn't change. But your weight depends on how much gravity is acting on you at the moment. You'd weigh less on the moon than on Earth, and in interstellar space you'd weigh almost nothing at all. But if you stay on Earth, gravity is always the same, so it really doesn't matter whether you talk about weight or mass.

• Macroscopic refers to matter that is large enough to be seen

• All of your observations in chemistry, and everywhere else, start from this perspective.

Macroscopic View of Matter

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

• The term submicroscopic describes matter that is so small that you cannot see it even with the most powerful microscope.

Submicroscopic View of Matter

• This gives you a glance into the world of atoms.

• You should know by now that matter is made up of atoms!

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

Using Models in Chemistry

Using Submicroscopic Models in Chemistry

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

Comparing the Structures of Aspirin and Sucrose

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

aspirin sucrose

Qualitative vs Quantitative

• A qualitative observation is one that can be made without measurement. You use your senses.

•A quantitative observation is one that utilizes measurement. You use a tool to get a number.

Pure substance or a mixture?

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

• Ex: water = H2O2 hydrogen atoms + one

oxygen

• 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.

• Ex: salt water – can have different amounts of salt in different areas


• A physical change is a change in matter that does not involve a change in its chemical identity.

• Examples of physical changes include:

• boiling, • freezing, • melting,

• evaporating, • dissolving, • and crystallizing.

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

Matter can be separated based on its physical properties. A sand/ water mixture can be filtered. A salt water mixture can be separated by evaporation.

• 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).

SolutionA mixture that looks the same

throughout.

Another name for “solution” isHomogeneous mixture

Solutions

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

• Ex: brass, stainless steel

• 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 (as in the sugar/water mixture), the solution is called an aqueous solution.

Solutions

• 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.

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

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

• There are two types of heterogeneous mixtures.

• A suspension is when tiny particles remain suspended in a liquid and may not be visible to the eye.

• A colloid is when the particles can be seen.

Heterogeneous mixtures

• Homogeneous mixtures are the same throughout.

• Another name for a homogeneous mixture is solution.

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

• Some solutions are solid. Alloys like brass is a solid solution.

• Solutions do not have to be liquid or contain water.

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Elements and Compounds

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Chemistry and Matter: Basic Concepts


Elements and Compounds

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

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

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

Elements & Compounds

• 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.

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 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 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 FormulaCaffeine C8H10N4O2

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Compounds Are More Than One Element• 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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*The END of Section 1.

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 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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Chemical Reactions and Energy• 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 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 is the science that investigates and explains the structure and properties of matter

Documents

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space matter

doesnt matter

mass weight

behavior of matter

properties of matter

submicroscopic view

object weight