Modeling the Atoms in the Chemical Reactions with the Element Cards Model the Atoms in the Chemical Reactions You Just Performed
Total Page:16
File Type:pdf, Size:1020Kb
UNIT 3 CHEMICAL REACTIONS L7ATOMS IN CHEMICAL REACTIONS What happens to atoms during chemical reactions? OBSERVING PHENOMENA Carefully observe as your teacher places a piece of steel wool on a ceramic plate and places both on the digital balance so you can observe the mass of the steel wool. Your teacher lights the steel wool on fire. Note any patterns of change in mass as the steel wool burns. Consider if this could be related to structural changes at an atomic level. OBSERVING PHENOMENA Phenomenon: Burning steel wool causes the mass of the steel wool to increase. What questions do you have about this phenomenon? Introduction A car sits in a field, rusting. Over time, the rust builds up thickly on the once-smooth steel parts of the car, parts containing iron. It seems to grow, as the rust gets thicker and thicker. The iron- containing parts get heavier and heavier, until the rust crumbles away, leaving jagged holes. What is happening here? Is matter disappearing or appearing? Although it may seem like matter is appearing out of nowhere as the rust grows, the extra mass comes from oxygen in the air. A chemical reaction has occurred in which atoms of iron and oxygen come together to form a new substance: iron oxide, or rust. You have already learned about substances and their properties. You also learned about chemical reactions and how to identify whether they have occurred by testing the properties of the substances. Now, you will explore what happens at the atomic level during chemical reactions. In this lesson, you will learn how atoms in chemical reactions regroup to form new substances. You will learn that the total number of atoms involved in a chemical reaction does not change. Thus, their total mass does not change either. Finally, you will learn how engineers use chemical reactions to make products in more environmentally friendly ways by analyzing the results of chemical reactions. Sec 1. Atoms Regroup in Chemical Reactions p106-107 Thinking of Atoms in Chemical Reactions • Chemical reactions occur when the bonds between atoms in the reactants break and reform to make new substances – the Products • The atoms that made up the molecules and extended structures of the reactants can form new molecules and extended structures in the products. Sec 1. Atoms Regroup in Chemical Reactions p106-107 A chemical reaction occurs when the bonds between the atoms of oxygen and hydrogen break within a water molecule. These atoms then form new bonds to produce oxygen gas and hydrogen gas. Atoms that are regrouping in this chemical reaction. Sec 1. Atoms Regroup in Chemical Reactions p106-107 When electric current passes through water, a reaction called electrolysis can take place. During the reaction, the bonds between the atoms of water molecules break and reform between pairs of hydrogen atoms or pairs of oxygen atoms. The chemical reaction has produced the molecules of two different substances: O2 and H2. Since there are twice as many atoms of hydrogen as there are atoms of oxygen, the tube on the left, which contains hydrogen gas, contains twice as much gas as the tube on the right. Sec 1. Atoms Regroup in Chemical Reactions p106-107 Writing Chemical Reactions To describe how atoms regroup during reactions, scientists write equations using chemical formulas and element symbols. Chemical equations are shorthand notations that describe chemical reactions. Sec 1. Atoms Regroup in Chemical Reactions p106-107 Annotate the image with the following labels: • Reactants • Products • Chemical bond Then, in red, circle the chemical bonds that break. In blue, circle the chemical bonds that formed. This is not really “your choice” I would like you to draw pictures of the atoms in the reaction and chemical Equation You may use examples in book or online Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Molecules Break Apart Decomposition Reaction In some reactions, groups of atoms that make up one substance break apart. These atoms form new groups of atoms that make up two or more other substances. Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Molecules Break Apart Decomposition Reaction In some reactions, groups of atoms that make up one substance break apart. These atoms form new groups of atoms that make up two or more other substances. Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Atoms of Multiple Substances Combine Synthesis Reaction In some chemical reactions, the molecules or extended structures that make up two or more substances join together to form new groups of atoms that make up a single substance. When atoms New chemical of iron and bonds form molecules of between the oxygen react, oxygen atoms the bonds and the iron between the atoms to make molecules of the extended oxygen structure iron break. oxide. Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Atoms Switch Places Displacement Reaction In some chemical reactions, atoms within one group swap places with atoms within another group. The lead atom swaps places with the potassium atoms to produce lead iodide and potassium nitrate. 3. Conservation of Matter Scientists describe this idea in the law of conservation of matter, a scientific law that states that matter cannot be created or destroyed. This law means that matter is not created or destroyed during state changes, chemical reactions, or any other changes in matter. A scientific law is a verbal or mathematical description of a natural phenomenon. For example, conservation of matter can be stated as: matter before reaction = matter after reaction why the mass does not change in a chemical reaction between acetic acid (vinegar) and sodium bicarbonate (baking soda). Since the atoms are neither created nor destroyed, the overall mass remains the same. The atoms have simply rearranged to form new substances. 3. Conservation of Matter 3. Conservation of Matter Equations Model Conservation of Matter in Chemical Reactions In all chemical reactions, the atoms of the reactants regroup to form new combinations in the products. No matter how atoms rearrange, the number of atoms does not change. In most chemical reactions, atoms break apart and then join together, swapping places. This diagram shows the chemical reaction that occurs when someone takes an antacid for digestive pains. 3. Conservation of Matter No matter which way atoms regroup during a chemical reaction, atoms never appear out of or disappear into thin air. The law of conservation of matter states that matter cannot be created or destroyed during a chemical reaction. For example, when baking soda and vinegar are mixed, the reaction forms water, sodium acetate, and carbon dioxide. If you count the number of atoms in the reactants and the products, you will notice that they are the same before and after the reaction. Fill out the following table with the number of each element in the chemical reaction. Reactants Products Acetic acid Sodium Sodium acetate Water Carbon dioxide bicarbonate H (hydrogen) C (Carbon) O (Oxygen) Na (Sodium) Use the information in the table to explain why the mass does not change in a chemical reaction between acetic acid (vinegar) and sodium bicarbonate (baking soda). 3. Conservation of Matter C2H4O2 + NaHCO3 → NaC2H3O3 + H2O + CO2 If you count all of the atoms, you will find that the number of atoms in the reactants (14) equals the number of atoms in the products (14). INVESTIGATION 1 MODELING CHEMICAL REACTIONS Think about what you observed when steel wool was burned. What patterns can you use to identify whether or not a chemical reaction has happened? The properties of the substances change since a new substance has formed. You could measure the properties of the substance each time it changes colors. INVESTIGATION 1 MODELING CHEMICAL REACTIONS What is happening to the atoms during a chemical reaction? Atoms are so small that you cannot see how they interact using a conventional microscope. How can you possibly know what is going on if you cannot see it? You can use models. INVESTIGATION 1 MODELING CHEMICAL REACTIONS For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS Now, use your model to answer the following questions: Count the atoms before and after a chemical reaction. What do you notice? There is the same number of atoms & same types of elements before and after a chemical reaction. – They are just rearranged What do you notice happens to the chemical bonds between the atoms? Chemical bonds are broken and then reform between different atoms form different molecules and extended structures. What do you notice about the molecule size before and after a reaction? Molecules can get bigger or smaller depends on the number of atoms in the molecule INVESTIGATION 1 MODELING CHEMICAL REACTIONS Think back to the PhET simulation you worked with. What are the similarities and differences between the simulation and the Element Card model you used.