Matter Chapter 2
Section 1: What is Matter?Objectives • Explain the relationship between matter, atoms, and elements. • Distinguish between elements and compounds. • Describe molecules, and explain how they are formed. • Interpret and write some common chemical formulas. • Categorize materials as pure substances or mixtures.
What is Chemistry? • Chemistry is about: what things are made of, what their properties are, and how they interact and change. • Chemistry is an important part of your daily life. Everything you use, from soaps to foods to carbonated drinks to books, you choose because of chemistry- what those items are made of, their properties, and the way they change and interact with other substances. • Why do you think pop is better in an aluminum can than a paper bag?
Composition of Matter • Matter is anything that has mass and occupies space (or has volume). • All the materials you hold, touch, wear, eat, and breathe are matter. Matter is made of molecules, which are made of compounds, which are made of elements, which are made of atoms. Matter <- molecules <- compounds <- elements <- atoms
Atoms • An atom is the smallest unit of an element that has all the properties of that element. • Atoms are the building blocks of matter.
Elements • Elements are substances that cannot be broken down or separated into simpler substances by chemical or physical means.
Compounds • Compounds are substances made of atoms of two or more different elements that are chemically combined.
Molecules • A molecule is the word used to describe the smallest unit of a substance that keeps all its original properties; it can consist of two or more atoms of the same element, or two or more different elements.
Elements and Symbols • Each element is designated by a one- or two-letter symbol that is used worldwide. • Symbols for elements are always a single capital letter or a capital letter and a lower-case letter.
Elements and Compounds • Since compounds are made of elements that each have unique properties and interactions, it makes sense that the compounds would have unique properties and interactions. • When elements combine to make specific compounds, the elements always combine in the same proportions. (2 H, 1 O) • The properties of the compound may differ from the properties of the elements involved. Table salt is a toxic green gas and an explosive metal.
Elements and Molecules • Atoms can join to make millions of molecules, just like letters of the alphabet can make millions of words. • Most molecules are made of atoms of different elements, such as water. A molecule may also be made of atoms of the same element, such as hydrogen gas (H2).
Chemical Formulas • A combination of chemical symbols and numbers used to represent a substance is a chemical formula. C16 H10 N2 O2 16 carbon atoms 10 hydrogen atoms 2 oxygen atoms 2 nitrogen atoms
Pure Substances • A pure substance is a sample of matter, either a single element or a single compound, that has definite chemical and physical properties. • A pure substance has only molecules of ONE substance in it. For example, a lakeful of water with one drop of salt in it is not a pure substance.
Mixtures • A mixture is a combination of two or more substances that are not chemically combined. • The amounts of substances in a mixture do not have to be the same every time. • A mixture can be separated into its individual components, unlike pure substances. • Most of the foods we eat, the things we drink, and the air we breathe are mixtures.
Types of Mixtures • Heterogeneous Mixture - the substances aren’t mixed uniformly and are not evenly distributed, therefore, easily separated. • Homogeneous Mixture - the components are evenly distributed, the mixture is the same throughout, and it is not easily separated.
Mixtures v. Compounds • While a compound is different from the elements that it is composed of, a mixture may have properties that are similar to the pure substances that form it. • For example, although you cannot see the parts of grape juice, you can observe properties of its two main ingredients: water and sugar. How?
Section 1 Summary • Matter has mass and occupies space. • An element is a substance that cannot be broken down into simpler substances. • An atom is the smallest unit of a element that has the properties of the element. • Atoms can combine to form molecules or compounds. • Chemical formulas represent the atoms in compounds and molecules. • A mixture is a combination of two or more pure substances. Mixtures can be heterogeneous or homogeneous.
Section 2: Properties of MatterObjectives • Distinguish between the physical and chemical properties of matter, and give examples of each. • Perform calculations involving density. • Explain how materials are suited for different uses based on their chemical properties, and give examples of each. • Describe characteristic properties, and give examples.
Physical Properties • Physical properties are often easy to observe, and easy to change. • Properties such as color, size, shape, and state of matter are physical. • You typically use physical properties to identify substances: for example, you recognize people by their hair color, height, eye color, etc. When playing football, you don’t use a tennis ball because it’s the wrong shape, size, color. • Mass, volume, weight, and density are also physical properties of matter.
Using Physical Properties to Describe Matter • You can use your senses to observe most properties of matter: shape, color, odor, and texture. • Other physical properties, such as melting point, boiling point, strength, hardness, and the ability to conduct electricity, magnetism, or heat, can be measured.
State of Matter • State of matter, or phase, tells the physical form in which a substance exists. • The main three are: solid, liquid, and gas. • The picture shows the solid, liquid, and gas states of water at the molecular level.
Density • Density is a measurement of how much matter is contained in a certain volume of a substance. A substance that has low density is “light” in comparison with something that has a the same volume.
Density Equation • Density = mass / volume or d = m / v • Density is measured in g/ml or g/cm3 • If you are measuring the density of a liquid, you would use g/ml • If you were measuring the density of a solid, you would use g/cm3 • A cm3 contains the same volume as a ml.
Practice Problems • If 10.0 cm3 of ice has a mass of 9.17 g, what is the density of ice? • Mass = 9.17g • volume = 10.0 cm3 • D = m/v • Density = 9.17g/10.0 cm3 • Density = 0.917 g/cm3 • If a 10 g block of wood has a volume of 2 cm3 , its density is 5 g/cm3. What happens to the density of the block if you cut it in half?
A piece of tin has a mass of 16.52 g and a volume of 2.26 cm3. What is the density of tin? • A piece of metal has a density of 11.3 g/cm3 and a volume of 6.7 cm3. What is the mass of this piece of metal?
Chemical Properties • Chemical properties are generally not as easy to observe as physical properties. • They are related to the specific elements that make up substances. • A chemical property describes how a substance changes into a new substance, either by combining with other substances or by breaking apart into new substances. • Chemical properties include flammability and the reactivity with water, oxygen, acid, or other substances.
Characteristic Properties • The properties that are most useful in identifying a substance, such as density, solubility, and reactivity with acids, are its characteristic properties. • Characteristic properties can be physical or chemical. The characteristic properties of a substance are the same whether you are observing a large sample or a small sample.
Section 2 Summary • Physical properties can be observed or measured without changing the composition of matter. • Physical properties help determine how substances are used. • They density of a substance is equal to its mass divided by its volume. • Chemical properties describe how a substance reacts; they can be observed when one substance reacts with another. • Scientists use characteristic properties to identify and classify substances.
Section 3: Changes of MatterObjectives • Explain physical change, and give examples of physical changes. • Explain chemical change, and give examples of chemical changes. • Compare and contrast physical and chemical changes. • Describe how to detect whether a chemical change has occurred.
Physical Changes • A physical change occurs when one or more physical properties are affected without changing its identity. For example, ripping a piece of paper has changed the size of the paper, but it’s still paper. • Some examples of physical changes are dissolving sugar, melting ice, sanding a piece of wood, crushing a can, mixing oil and vinegar, and getting a hair cut.
Key Things About Physical Changes • Physical changes do not change a substance’s identity. After a physical change, a substance may look different, but the arrangement of atoms that make up the substance are not changed. • Dissolving IS a physical change. The molecules of sugar dissolved in water have not changed, they have simply changed states of matter.
Mixtures and Physical Changes • Because the substances in a mixture are not chemically combined, separating them is a physical change. • Each substance in the mixture keeps its identity, and each component has the same chemical makeup it had before the mixture was formed. • Unlike mixtures, compounds can only be broken down through chemical changes. • Some ways to separate mixtures include heating to evaporate, using a magnet, centrifuging, and distillation or filtration.
Chemical Changes • A chemical change occurs when one or more substances are changed into entirely new substances that have different properties. • Milk turning sour, alka-seltzer reacting in water, and the rusting of metal are all chemical changes.
Key Things About Chemical Changes • Chemical changes form new substances that have different properties. For example, when you bake a cake, you combine eggs, flour, butter, water, oil, sugar, milk, baking powder, and other ingredients. When baking powder reacts with water, it produces carbon dioxide, causing the cake to rise. When you mix the other ingredients, you end up with something entirely different from what you started with.
Chemical changes can be detected by looking for certain clues. A change in odor or color is a good clue. When food burns, you can often smell the gases given off. When bubbles form, that’s usually a good clue as well. Fizzing, foaming, or the production of sound, heat, light, or odor are all good clues.
Because new substance are formed during a chemical change, you cannot reverse the process using physical changes. • Some chemical changes can be “undone” using chemical changes. Usually, electricity is involved. To change water into its individual components, it can be shocked to form hydrogen and oxygen. • Compounds can be broken down through chemical changes. When you open a bottle of pop, you are observing the breakdown of carbonic acid into carbon dioxide and water.
Physical v. ChemicalSection 3 Summary • Physical changes are often easily reversed. • Physical changes usually result in a change in a physical property. • Dissolving is a physical change. • Physical changes do not change the identities of the original substances. • Chemical changes require another chemical change in order to reverse. • Chemical changes result in a change in color, odor, light, heat, or sound. • Production of bubbles is a chemical change. • Chemical changes produce -new substances with new properties.