Lesson 4: Molecular Structure PDF

LESSON 4 Classification and States of Matter Molecular Structure Key Conecpt How do atomic structures determine the properties What do you think? Read the two...

LESSON 4 Classification and States of Matter Molecular Structure Key Conecpt How do atomic structures determine the properties What do you think? Read the two statements below and decide of a substance? whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After A  ll compounds have high melting and boiling points. Metal and nonmetals have the same properties. Study Coach Make an Outline Outline How do elements differ? the information in this An element is a substance made of only one type of atom. lesson. Use the headings as the main divisions of Each element’s name is found on the periodic table of elements. your outline. Include Types of Elemental Substances Elements are made of important details under individual atoms, but those atoms can be arranged into different each heading. Use your kinds of structures. Some substances, such as helium and neon, outline to review the lesson. are made up of individual atoms that are not attracted to one another. Some substances are molecules, a group of atoms that are held together by chemical bonds and act as a unit. Examples Scientific Vocabulary Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. include hydrogen, oxygen, and chlorine. The figure below shows chemical bond (noun) a force that holds hydrogen molecules. A third type of substance is individual two or more atoms atoms of the same type connected to form extended structures. together Academic Vocabulary individual (adjective) existing separately from others 20 Classification and States of Matter Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED. RE_P312_416A_NGMSS-BANK  Properties of Metal and Nonmetals The properties and behaviors of a substance can be observed. These observed properties are due to the structure of the atoms and molecules in the substance, which cannot be observed because atoms are too small to be seen with light microscopes. Elements can be classified into groups based on their structures and their properties. Nonmetal Gases Many nonmetals are gases at room temperature. These gases are usually either individual atoms, shown below on the left, or they are diatomic molecules, shown below on the right. When a molecule is diatomic, it is made of two atoms that are the same. Individual atoms Molecules Atoms or molecules of nonmetal gases have low attraction to each other. This means they have high potential energy and high kinetic energy. In turn, this means that these gases boil at very RE_P312_435A_NGMSS-BANK low temperatures. It is easy for these gas particles to escape attractions to their neighboring particles. Due to the large Scientific Vocabulary Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. amount of space between particles, these gases do not conduct conduct electricity or thermal energy. The gas particles cannot easily (verb) to serve as a transfer charge or energy to other gas particles. medium through which something can flow Nonmetal Solids The nonmetal solids are individual atoms of the same type that are connected. They form an extended structure. The attraction between the atoms is low. This makes the substance brittle and dull. Nonmetal solids, like nonmetal Scientific Vocabulary gases, are poor conductors of electricity or thermal energy, conductor because they have a low attraction between atoms. These (noun) a material that substances have low potential and kinetic energy as compared to allows heat, light, sound, or electric charge to flow gases. Most nonmetal solids have low melting points compared from one thing to another with solid metals. Reading Essentials Classification and States of Matter 21 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Metals Almost all metals are solid at room temperature. This is because metal atoms are attracted to one another and form extended structures. Many metals are shiny. Most are malleable. That means the closeness of the atoms allows them to slide past each other instead of breaking when the substance is bent or hammered. For example, you can bend a metal paperclip without breaking it. The closeness of the atoms also means that electric charges and thermal energy can easily pass from one atom to the next. Metals have low potential and kinetic energy. That means a greater amount of thermal energy must be added to change the solid to a liquid. This is why metals have very high melting and boiling points. How do compounds differ? You have read that the properties of elements differ. What happens when elements combine? Compounds make up most of the matter around you, including living and nonliving things. How do the properties of compounds differ from the properties Scientific Vocabulary of elements and from one another? compound Types of Compounds Atoms can form complex molecules. (noun) matter that is Some molecules contain a few atoms and some have thousands made up of two or more of atoms. Individual atoms of different types can repeat to form different kinds of atoms extended structures. The sodium chloride shown below is an joined together by chemical bonds example of a compound that can form an extended structure. Sodium chloride is also known as table salt. This type of structure usually forms between atoms of a metal and a nonmetal of opposite charges. This is true for table salt. Sodium is a metal. Chlorine is a nonmetal. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. RE_P312_420A_NGMSS-BANK 22 Classification and States of Matter Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Molecules Recall that some elements are molecules. They are made up of two of the same type of atom. Some compounds are also molecules. Compound molecules are made up of different types of atoms. Some molecules are not attracted to one another. Carbon dioxide, shown below on the left, is an example of this type of molecule. Other compound molecules are attracted to each other. These molecules come together to form extended structures. The sugar shown below on the right is one example of this type of molecule. These different structures give compounds different properties that can be observed. Properties of Ionic and Covalent Compounds The RE_P312_410A_NGMSS-BANK properties of compounds are related to their atomic structures. RE_P312_408A_NGMSS-BANK Just like elements, compounds can be classified into groups based on their structures and their properties. Ionic Compounds Ionic compounds are formed from atoms that have opposite charges. The atoms have a strong force of attraction to each other, due to their charges. Because of this, ionic compounds form extended structures as solids. These Scientific Vocabulary Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. structures can form crystals. The strong attractive forces give crystal ionic compounds their properties. Ionic compounds have high (noun) a solid, with an melting and boiling points. Ionic compounds are brittle because orderly, repeating pattern when they are hit with a force, the atoms separate from each other. Many ionic compounds will dissolve when placed in Scientific Vocabulary water. Water with an ionic compound dissolved in it is a good brittle (adjective) easily broken conductor of electricity. or cracked Extended Structures Extended structures made of the same atoms are elements. Extended structures made of two or more Scientific Vocabulary different atoms are compounds. dissolve (verb) to blend two or more substances together to make a solution Reading Essentials Classification and States of Matter 23 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Properties of Covalent Compounds Covalent compounds form molecules. Recall that a molecule is a group of atoms that are held together by bonds and act as a unit. Covalent compounds usually have low melting and boiling points. They are usually gases or liquids at room temperature. They are poor conductors of electricity and thermal energy. Polar Covalent Compounds Atoms of the elements carbon, hydrogen, and oxygen have strong attraction to one another. They form many different molecules. One molecule they form is sucrose, also known as table sugar. The chemical formula for sugar is C12H22O11. Every sugar molecule has these atoms in the same pattern, as shown below. A molecule of sugar is attracted to other molecules of sugar. The groups of molecules make a crystal structure. These molecules attract each other strongly. They have high melting and boiling points. These molecules dissolve in water. Nonpolar Covalent Compounds Another type of compound is a nonpolar covalent compound. Nonpolar covalent P312_434A_NGMSS-BANK compounds, such as carbon dioxide, are not attracted to like molecules. They have very low melting and boiling points. Most are a gas at room temperature, but some can be solids or liquids. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. These molecular substances are dull and melt or evaporate at low temperatures. They do not dissolve in water. Nonpolar covalent compounds also do not conduct electricity. To Dissolve or Not to Dissolve A nonpolar covalent Academic Vocabulary compound will not easily dissolve in a polar compound. It will simplify dissolve in other nonpolar compounds. This idea is simplified to (verb) to make easier to the phrase “like dissolves like.” This means that polar covalent understand compounds can dissolve other polar compounds. Similarly, nonpolar compounds can dissolve in other nonpolar compounds. Sugar and water are both polar compounds. Water easily dissolves sugar. Oils are nonpolar compounds. Oil does not dissolve in water. The atomic structure of these substances explains why sugar will dissolve in water but oil will not. 24 Classification and States of Matter Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. Reading Essentials Classification and States of Matter 25 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.