Introduction (p23) Vitamin C No, that's not your friend's latest art project. In fact, it's a ball-and-stick model of vitamin C. You have eaten vitamin C in some form or another. You may have eaten it in oranges, drunk it in lemonade, or even chewed and swallowed it in your vitamins! But it didn't look at all like this model. That is because the model represents the shape and chemical makeup of just one tiny unit of vitamin C. This unit is a particle called a molecule. A molecule of vitamin C is made up of 20 atoms. That may sound like it is a pretty large molecule, however, it is actually millions of times smaller than the period at the end of this sentence. In fact, it is actually one of the smaller molecules in the world! Each molecule of vitamin C consists of atoms of carbon, hydrogen, and oxygen. The specific numbers of each type of atom and the particular ways they are attached to one another make vitamin C an important part of a nutritious diet. In this lesson, you will use models to explore how atoms of elements group together to form the many different materials and objects in the world around you. Though they occur on the atomic scale, by using proportional models, you will visualize how atoms combine. Lesson 2 How are atoms combined to form different molecules and extended structures? 1. Molecules and Chemical Bonds (p24-25) There are only 92 elements that occur in nature. Yet, there are millions of materials on Earth. If there are only 92 unique elements in the world, how is it possible to have the many different materials that occur naturally? 1. Molecules and Chemical Bonds (p24-25) Atoms of elements can come together to form more complex particles. Ex: oxygen and hydrogen are each made up of only one kind of atom. Atoms of hydrogen and oxygen can be joined together to form more complex particles. The connections between atoms in these more complex particles are called chemical bonds. The new bonded particle is called a molecule and is made of two or more atoms that are connected by chemical bonds. There is a chemical bond holding each You, your classmates, and even many of the materials in your classroom are made hydrogen atom to the oxygen atom. of atoms bonded together to form molecules. 1. Molecules and Chemical Bonds (p24-25) • Not all atoms make chemical bonds. • The noble gases—such as helium, neon, and argon—do not form bonds with other atoms. (Inert) • But most atoms are not stable unless they are bonded with at least one other atom to form a molecule, or a group of two or more atoms held together by chemical bonds. Valence electrons are in the outmost shell of electrons and these are the electrons that hold molecules together 1. Molecules and Chemical Bonds (p24-25) Molecules are also too small to be seen. To portray molecules, scientists use models. A model is a representation of an object that makes important aspects easier to see. Scientists use models to show the different atoms in a molecule and how the atoms are bonded together. By using models, they can quickly depict (show) molecules in a visual way that everyone can see. 1. Molecules and Chemical Bonds (p24-25) Hydrogen - white or gray spheres. 2D & 3D Models Oxygen - red spheres. Carbon -black spheres. Since atoms appear as round spheres in models, regardless of what element they are, scientists often use different colors to represent different elements. Scientists can: 1) Quickly identify elements in a molecule 2) Quickly identify shape of a molecule 3) Easily visualize what the model looks like (with out using other tools) 1. Molecules and Chemical Bonds Review 1. Look closely at this model. Circle all of the chemical bonds in red. Then, put a blue triangle around each atom. 1. Molecules and Chemical Bonds Review 2. Explain why the above model is a good representation of a molecule. Be sure to include the following terms in your answer: atom and chemical bond. The model is a good representation of a molecule because it shows the atoms and chemical bonds that make up that molecule. It allows for a person to "see" a molecule, even though it is too small to be seen without special tools. 3. Different models have benefits and drawbacks. What is a drawback of the above model? Explain how you would improve the above model. The model is a picture of a 3D model, so you cannot rotate it. It would be better to build with spheres and connections so you can rotate it. Investigation: Modeling Chemical Bonds, You will use your Molecular Molecules and Extended Structures Modeling Set to create models of molecules. Examine your kit. •What are some things you notice about each of the colored objects? •What do you think the colored objects represent? •Are they all the same size? •What do you think the white rods represent? Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Chemical Bonds When atoms connect with other atoms, the result is a chemical bond. Chemical bonds are responsible for the large number of molecules found in nature or created in laboratories. Look at the model atoms in your Molecular Modeling Set. Then, complete the chart in your notebook. Atom Type Model Color Bonds Possible Hydrogen White 1 Oxygen Red 2 Nitrogen Blue 3-4 depends on temp Carbon Black 4 2) In your notebook, work with a partner to: Investigation: Modeling Chemical Bonds, •Identify the number of elements in each molecule. Molecules and Extended Structures •Identify the number of atoms in each molecule. •Identify the number of bonds occurring in each molecule. •Create a model of each molecule using your Molecular Modeling Set. 1 2 1 1 2 2 1 2 3 2 2 2 3) In your notebook, work with a partner to: Investigation: Modeling Chemical Bonds, •Identify the number of elements in each molecule. Molecules and Extended Structures •Identify the number of atoms in each molecule. •Identify the number of bonds occurring in each molecule. •Create a model of each molecule using your Molecular Modeling Set. 2 4 3 2 3 2 2 4 3 2 3 4 Analyze this video, then turn and Investigation: Modeling Chemical Bonds, discuss the following questions Molecules and Extended Structures with your partner: •How many carbon atoms are in this molecule? 5 •How many hydrogen atoms are in this molecule? 9 •How many nitrogen atoms are in this molecule? 1 •How many oxygen atoms are in this molecule? 4 What might be the chemical formula for this complex molecule? C5H9NO4 Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Analyze Videos 1 and 2, then turn to discuss the following questions with your partner: What features are shared by both of these molecules? Both molecules contain carbon and hydrogen and have a chain-like structure. What features make these molecules different? Different atomic composition. The molecule in Video 2 has Oxygen atoms. Investigation: Modeling Chemical Bonds, Molecules and Extended Structures 2 5 4 4) In your notebook, work with a partner to: •Identify the number of elements in each molecule. •Identify the number of atoms in 2 8 7 each molecule. •Identify the number of bonds occurring in each molecule. •Create a model of each 11 molecule using your Molecular 2 10 Modeling Set. Do not disassemble the propane and propyne 2 9 9 models you created. 2 7 8 Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Consider the propane and propyne models you created. Propane Are there any similarities in the structure of each molecule? Both have 3 carbon atoms in a chain shape. Both contain hydrogen Consider both as hydrocarbons Are there any differences you notice? Propane - 8 hydrogens Propyne - 4 hydrogens. Propyne What differences in these two molecules might account for their different properties? Their different chemical compositions. They would have different properties/characteristics 2. Composition and Structure of Molecules (p26-27) Molecules come in all sorts of shapes and sizes. Simple Molecules The simplest molecules are composed of only two atoms, which can either be of the same element or of different elements. Scientists often use chemical symbols to write the names of molecules and substances as a chemical formula. Subscripts are used for more than one type of atom. For example: •Hydrogen gas → H2 •Oxygen gas → O2 •Nitrogen gas → N2 • Carbon dioxide → CO2 2. Composition and Structure of Molecules (p26-27) Molecules come in all sorts of shapes and sizes. ammonia caffeine A unique molecule always has a unique composition methanol and structure. C8H10N4O2 2. Composition and Structure of Molecules (p26-27) Atomic composition refers to the number and type of composition atoms in a molecule. The atomic composition of a substance includes both the types of elements that make it up, as well as the specific number or ratio of atoms of each kind of element that make it up. Both aspects of composition affect substances characteristics and what it looks like. Molecules can differ in the elements that compose them and the ratio of those elements. Both water and hydrogen peroxide are made up of only the elements hydrogen and oxygen. These two compounds have different characteristics because they have different numbers of these two elements. disinfectant drink and bathe 2. Composition and Structure of Molecules (p26-27) structure Another factor that affects the characteristics of a substance, and can even determine its identity, is the chemical structure of its molecules. Chemical structure of a molecule refers to the specific arrangement of its atoms.