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Chapter 2 T HE CHEMICAL VIEW OF MATTER. Chapter Learning Objectives. By the end of the chapter, you will recognize that The different types of atoms are called elements, which are arranged systematically in the periodic table.
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Chapter Learning Objectives By the end of the chapter, you will recognize that The different types of atoms are called elements, which are arranged systematically in the periodic table. The building blocks of matter are atoms, which combine to form compounds. Matter can exist as mixtures or pure substances. Changes in matter can either be a physical or a chemical change and energy is the ability to do work
Chapter Learning Objectives (cont) Matter can be classified once elements have combined into compounds where only chemical reactions can separate them. All atoms of one element are identical to each other but different than the atoms of other elements. Combinations of chemical symbols for elements are used to represent stable combinations of atoms into molecules. Scientific facts and laws are established through accurate observations and measurements.
Chapter Outline • The Chemical View of Matter • Elements are the simplest kind of matter. • Most materials you handle are pretty complex in their structure, and many are mixtures. • Hydrogen is the 1st element in the periodic table. • The chemical model of matter starts with the following: a pure substance, an element, and an atom. • Comparing the element of helium and mercury.
Definitions A pure substance is something with a uniform and fixed composition at the micro/nanoscopic level. Pure substances can be recognized by the unchanged nature of their properties. Ex. Fresh air (N and O), water (H and O) or brass alloys, (Cu and Zn) An element is a pure substance composed of only one kind of atom. Ex. H, He, O, Br, Kr, etc… An atom is the smallest particle of an element, and the atoms of different elements are different. Ex. Helium atom vs. Mercury atom
The element hydrogen on theperiodic table: atomic number and mass
Comparison between Helium and Mercury What does that mean from a chemical point of view? First, neither helium or mercury cannot be broken down or separated down into any other kind of matter, still recognized as helium or mercury. Second, both contains very, very small particles known as helium or mercury atoms. Ex. Helium in a balloon and mercury in a thermometer and some thermostats Third, helium and mercury each have a unique and consistent set of properties by which they can be identified. Ex. Helium exists as a gas and mercury a liquid, helium is light while mercury is heavy, mercury conducts electricity and helium does not, and size.
Comparison between Helium and Mercury, cont. Fourth, helium and mercury have in common that they are both elements and each is composed of a single kind atom.
Lead paint can threaten children's health Credit: Getty Images
Napoleon: victim of arsenic poisoning? Credit: Bridgeman Art Library
The Chemical View of Matter • The combination of atoms are the building blocks for making a chemical compound. • Pure substances are not elements but rather a compound. • Different atoms linked together make a compound. • Water, carbon monoxide, and carbon dioxide are examples of a chemical compounds. • All matter consists of tiny particles called a molecule. • Experimentally, pure substance can be classified into two categories: chemical compounds or elements.
Pile of unorganized Legos Credit: Courtesy of Julie Millard
Molecules, like these Legos, can be combined in different ways Credit: Courtesy of Julie Millard
Molecules, like these Legos, can be combined in different ways Credit: Courtesy of Julie Millard
Definitions Chemical compounds are pure substances made of atoms of different elements combined in a definite, fixed ratios. Ex. Water will have the same property no matter where it comes from. A molecule is the smallest chemical unit of a compound that retains the composition and properties of the compound and can exist independently. Ex. 2H’s and 1O
Experimentally, pure substances are classified into 2 categories: • Chemical compounds, which can be broken down into simpler substances called elements. • Elements, which cannot be broken down into any smaller particle still recognizable as that element.
The Chemical View of Matter • Mixtures and Pure Substances. • Most samples of matter as they occur in nature are mixtures. • There are two types of mixtures that exists as heterogeneous or homogeneous mixtures. • Mixtures can be one of the three common states of matter. • Homogenous mixtures are referred to as solutions. • No amount of optical magnification will reveal a solution to be heterogeneous, because it is a uniform mixture of particles that are too small to be seen with regular light.
Mixtures and Pure Substances • Heterogeneous • Composed of particles that do not completely mix • Homogeneous • Have the same composition throughout the entire solution • Three types: solutions, colloids, and suspensions
Definitions Heterogeneous mixtures are not uniform in composition and clearly visible, such as chocolate chip cookies or the different kinds of crystals in many rocks.
Order of Ice, trapping water molecules at the microscopic level. Homogeneous mixtures are uniform in composition and are referred to as solutions. Ex. Also, clean air, freshly brewed ice tea, brass alloys, sugar, or table salt Solutions are homogenous mixtures which may be in the solid, liquid, or gaseous state. Ex. Mixing sugar in water, salt in water or freshly brewed ice tea
Heterogeneous mixture at the microscopic level What about blood, hetero or homogeneous mixture? Homogeneous at the macroscopic level Mixtures may appear to be homogeneous even if they are not, just like in blood, or the air in this room using a beam of light would show floating dust particles in the air. When a mixture is separated into its components, the components are said to be purified, just like in filtered drinking water! Fig. 2-7c, p. 24
The Chemical View of Matter Physical Changes versus Chemical Changes Physical changes involve changes in appearance and reversible (i.e., changes in state such as melting, mass, color, density, odor, etc…). Chemical changes result in new substances usually by an explosion, reaction, and non-reversible. Physical properties of substances are pinpointed by making numerical measurements (i.e., density) A chemical change or commonly a chemical reaction reactants (starting substances) and is converted into products (new and different substances.
The Chemical View of Matter • Physical Changes versus Chemical Changes cont. • Some physical and all chemical reactions are accompanied by changes in energy. • Energy is the ability to cause change or do work. • There are two types of energy: potential (stored) and kinetic (energy of motion )
Definitions In chemistry, the word physical is used to refer to processes that do not change chemical identities. Properties that can be observed without changing the identity of a substance are classified as physical properties. Iron vs. Sulfur Sulfur is yellow and iron is magnetic each have different properties of matter, but we can make the following observations: sulfur has color, pick up iron with a magnet, or measure its boiling point without changing its mass. Mass is a measure of the quantity of matter in an object. Density is mass per unit volume. The units are grams for mass (weight) and cubic centimeter (cm3) for volume of solids or milliliters (ml) for volume of liquids Ex. Density of lead is 11.3 g/cm3 and aluminum is 2.7 g/cm3 The mass of lead is heavier 11.3 g than aluminum that weighs 2.7 g but both solids can be compared to pieces of equal size, equal volume 1 cm3. Don’t get mass and density confused!
Definitions cont’ Processes that do result in chemical reactions and changes in the identity of one or more reactant are referred as chemical properties. For ex. Gasoline burning is converted to a mixture of CO2, CO, and H2O or the combination of H2 and O2 to form H2O are classified as a chemical property. The word chemical is used to describe processes that result in a change in identity.
Run the following web animations/movies. 2.1: Water Vaporization and Air Pressure 2.2: A Chemical Reaction Between Hydrogen and Oxygen
Is it a physical or chemical change? Are water molecules undergoing a physical or chemical change? Physical change because regardless if it undergoes changes from the solid, to liquid, to gas, it is reversible and still water. Is a stick of dynamite a physical or chemical change? Chemical change because it is due to an explosion, caused by a reaction and is irreversible. Turning on your car to go to school a physical or chemical change? Chemical change because it is due to an explosion, caused by a combustion reaction and is irreversible. Raking up leaves into a pile during a Fall day in October a physical of chemical change? Physical change because after raking the leaves the leaves didn’t change form.
Reactants Products D Ex. H2 + O2 H2O D All chemical reactions have the following in a reaction: Definitions Chemical Reaction is a process in which one or more pure substances are converted to one or more different pure substance and producing a new rearrangement of atoms. Reactants are substances that undergo chemical changes in a chemical reaction. Products are substances that are formed in a chemical reaction.
Observables indications of chemical reactions: (a) a flame, (b) mixing substances produces a glow, (c) a solid is formed after mixing, (d) there is a color change after mixing Fig. 2-5, p. 22
Some physical and almost all chemical reactions are accompanied by changes in energy. Energy is the capacity for doing work or causing change. Energy can either be absorbed or released in the form of heat! Heat is released during combustion or burning of chemical reactions but many chemical reactions such as photosynthesis requires energy to be absorbed from their surroundings. Two types of Energy to know: Potential Energy is stored energy, waiting to be used. Kinetic Energy is energy of objects in motion, which is converted from potential energy. p. 22
Run the following web animations/movies. 2.4: Energy Transfer
The Chemical View of Matter Classification of Matter. Types of Matter Pure substances (elements or compounds) Mixtures (homogeneous or heterogeneous) States of Matter Solids, liquids, gases are the common states of matter. The fourth state, plasmas, occurs in flames, stars, and the outer atmosphere of Earth The kinds of matter described – elements, compounds, and mixtures– can be classified according to their composition and how they can be separated into other substances.
Why Study Pure Substances? There are 3 basic reasons: 1. Only by studying matter can we understand how to truly utilize its properties, design new kinds of matter, and make desirable changes in the nature of everyday life. Ex. Swallowing extracts from the willow tree could relieve pain, although there were some unpleasant side effects. Once chemist identified the pain-relieving substance in the mixtures of extracts, they were able to create a molecule that was similar enough to relieve pain but with fewer side effects. This molecule is known as aspirin, represented as C9H8O4.
Synthesis of Derivatives The willow tree, source of the active ingredient of aspirin Aspirin (C9H8O4)
2. Studying the properties of matter helps us to deal intelligently with our environment, both in everyday life and in the social and political arena. Ex. Knowing something about the properties of fertilizers or pesticides helps us decide which ones to use, which ones to avoid, and when their use is or is not necessary or pouring waste down a sewer drain, what happens to it and how much will it cost to upgrade a sewage treatment plant? 3. The 3rd reason for studying the properties of elements and compounds is simple curiosity. Ex. Chemicals and chemical changes are a part of nature that is open to investigation. If we hope to understand matter, the first steps are to discover the simplest forms of matter and study their interactions. This curiosity draws many chemists to basic research.
The Structure of Matter Explains Chemical and Physical Properties An essential part of basic research is investigation into the structure of matter – how atoms of the elements are connected in larger units of matter and how these units are arranged in samples of matter large enough to be seen. Fig. 2-7a, p. 24
Run the following web animations/movies. 2.5: Separation of a Mixture
The Chemical View of Matter • The Chemical Elements • The elements range widely in their properties, such as gases, liquids, and solids. • Symbols for the elements is another language that must be learned, just as in music or a football play. • Denoting the 1 alpha or 2 alpha character symbol for shorthand notation of the elements. • Knowing both the chemical symbol and naming elements is how chemist communicate with one another.
The symbols and language in the margin are equally mysterious to anyone who has never been a musician or played football. Chemistry, just like music or football, needs special symbols and language. Without them, communication would be impossible. Some symbols are single letters that are the first letter of the name. Others are two letters from the name, always with the first letter capitalized and the second lowercase. Ex. Hydrogen is represented by H and indium is represented by In; nitrogen for N and nickel, by Ni; magnesium is represented by Mg and manganese, by Mn.
