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. 2. Composition and Structure of Molecules (p26-27) structure Butane and Isobutane both contain the same number of carbon and hydrogen atoms. However, their molecular structure is different. 2. Composition and Structure of Molecules (p26-27) structure Butane and isobutane both contain the same number of carbon and hydrogen atoms. However, their molecular structure is different. As a result, they have different properties, and people use them for different purposes. 2. Composition and Structure of Molecules (p26-27)
Carbon 8 Two ring-like Nitrogen 4 structures with two chain- Oxygen 2 like structures Hydrogen 10 and tripod-like structures attached to the Caffeine rings
Chemical Formula = C8H10N4O2 We did this part already
Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Extended Structures How large can molecules get? Look closely at this model of polyester. How many carbon atoms are there in this model? 59 Carbon atoms (in the image) How many hydrogen atoms? 49 Hydrogen atoms (in the image) How many oxygen atoms? 23 Oxygen atoms (in the image)
What is the atomic composition of polyester? It isn’t C59H46O23! It is C10H8O4 (subunit of C10H8O4 repeats.) Polyester has a structure that forms as a result of repeated patterns of molecules. These structures are called extended structures. Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Extended Structures Can you build polyester using your Molecular Modeling Set? If every group in the class combines their model components together, how large of a polyester chain can you make? Extended structures are made of smaller subunits that repeat. In polyester, the subunit is called an “ester”. Can you identify the ester in the photo? Build an ester.
C10H8O4 repeats. Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Extended Structures Explain how the visible patterns and physical properties polyester fabric are related to its chemical structures. Polyester is a thread-like (chain-like) structure. This makes it good to use in fabrics. Fabric stretchiness is due to its molecules being in a long linear shape Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Not all extended structures form chains. Many extended structures extend not just in 1 dimension, but in all 3 dimensions. A crystal is formed when atoms or molecules are arranged in a repeating, ordered pattern. Some crystals may be very small – like a grain of salt. Other crystals may form over many thousands of years to form large structures. Observe this image of a salt crystal. Investigation: Modeling Chemical Bonds, Molecules and Extended Structures What atoms are repeated to form a crystal of salt? Na, Cl What is the ratio of these atoms? 1:1 How would you describe the shape made by these atoms? It looks like a box, or cube. Investigation: Modeling Chemical Bonds, Molecules and Extended Structures Can you build a 3D model of salt? What materials would you use? In your groups, try to build a 3D model of salt. **** Explain how the visible patterns and physical properties table salt is related to its chemical structures. Table Salt’s hardness and grain- like appearance is due to its atoms being tightly packed in a cube shape
3. Crystals and Polymers p28-29 Crystals A crystal is a solid structure whose atoms or molecules are arranged in repeating, three-dimensional subunits. • formed with only one element or with multiple elements. • structures that could go on forever in all three dimensions. • Can observe patterns in the arrangement of atoms in simple geometric patterns like squares, cubes, pyramids or pentagons or hexagons.
Diamond is a crystal made of one element, carbon. The subunits that makes up a diamond crystal look like a cage made of carbon atoms. The atoms are held tightly in place, which makes diamonds good cutting tools for materials 3. Crystals and Polymers p28-29 Crystals Solid sodium chloride, also known as table salt, is another crystal made of repeating subunits. Each subunit is four sodium atoms and four chlorine atoms alternating to form a cube Table salt is also called NaCl because the sodium and chlorine atoms are in a 1 : 1 ratio. Table Salt’s hardness and grain-like appearance is due to its atoms being tightly packed in a cube shape 3. Crystals and Polymers p28-29 Crystals Graphite is made of thin sheets of carbon atoms bonded in hexagons. When you write with a pencil, the friction between the pencil and the paper cause the layers to scrape off of the rod of graphite and then stick to the paper. 3. Crystals and Polymers p28-29 Crystals Water is also a molecule that forms crystals when liquid water freezes to form ice. What molecules are repeated to form a crystal of ice? H₂O molecules How would you describe the shape made by the water molecules in this ice crystal? a hexagon
Crystals are molecules are arranged in a regular, repeating pattern. 3. Crystals and Polymers p28-29 Polymer A polymer is a structure that is made of smaller, repeating subunits in a chain.
In polymers the subunit is always a molecule. Polyester is made of repeating smaller molecules called “ester” molecules.
Polyester is a thread-like structure. This makes it good to use in fabrics. Fabric stretchiness is due to its molecules being in a long linear shape 3. Crystals and Polymers p28-29 Polymer A polymer is a structure that is made of smaller, repeating subunits in a chain. In polymers the subunit is always a molecule Polyester is made of repeating smaller molecules called ester molecules.
polyvinyl chloride, or PVC. polyethylene terephthalate, or PET 3. Crystals and Polymers p28-29 Polymer
The proteins that make up your muscles and the DNA that gives you your traits are all polymers.
All polymers made of many smaller molecule subunits that are bonded to each other in a chain. 3. Crystals and Polymers p28-29 Extended Structures
Crystals and polymers are considered extended structures Both have regular repeating subunits Crystal subunits are made of atoms and molecules – 3D Polymer subunits are made of only molecules - chain Modeling Molecules and Extended Structures Key Science Concept p30 Everything in the world is made of atoms of elements, and these atoms can combine to form molecules and extended structures. Scientists can use ball-and-stick models to describe the molecules and extended structures that make up the millions of different materials in the world around you. Modeling Molecules and Extended Structures Key Science Concept p30 Everything in the world is made of atoms of elements, and these atoms can combine to form molecules and extended structures. Scientists can use ball-and-stick models to describe the molecules and extended structures that make up the millions of different materials in the world around you.