Section III: A World of Particles Lesson 11 Atomic Pudding Lesson 12 Atoms By Numbers Lesson 13 Subatomic Heavyweights Lesson 14 Isotopia Lesson 15 Nuclear Quest Lesson 16 Old Gold

Lesson 11: Atomic Pudding Models of the Atom

Alchemy Lesson 11: Atomic Pudding ChemCatalyst The drawing shown here is a model of a very tiny cube of gold. 1. What do you think a scientific model is? 2. The spheres in this model represent atoms. What do you think atoms are? 3. How could you draw a model of the element copper to show that it is different from the element gold? meter

Key Question How are the smallest bits of matter described?

You will be able to: describe the historical development of the current atomic model describe and draw an atomic model and explain the evidence that supports the existence of atomic structures describe the dynamic nature of scientific models

Prepare for the Activity Work in groups. Model: simplified representation of something more complex facilitates understanding certain aspects of a real object or process. Atoms: smallest unit of an element that retains the chemical properties of that element

Discussion Notes The Atomic Model Through Time

Discussion Notes (cont.) Discovering Subatomic Particles: Electrons (e-) Cathode ray tube experiments = discovered a stream of negatively charged particles Thompson discovers tiny mass of particle = concludes particles smaller than atoms exist (plum pudding model) Nucleus Gold foil experiment = positively charged alpha particles shot at gold foil, most pass through, some rebound –Rutherford concludes rebounders hit the dense nucleus (also positively charged) –Nucleus is so dense that a nucleus the size of a. has the mass of 70 cars!

Rutherford’s Gold Foil Experiment Discovery of nucleus

Thompson and Cathode Ray Tube Discovery of electrons

Discussion Notes (cont.) An atom is mostly empty space. The rest consists of a nucleus, which is located in center of the atom, and electrons, which are located around the nucleus. The nucleus is very small if the diameter of the atom was 2 football fields the nucleus would be the diameter of a nickel

Discussion Notes (cont.) ParticleSymbolLocationCharge Relative Mass amu Mass (g) electrone-Outside nucleus x protonp+p+ In nucleus x Neutronn0n0 In nucleus x10 -24

Discussion Notes (cont.) Scientists have created models to describe atoms. Scientific evidence is a collection of observations that everyone agrees on.

Wrap Up How are the smallest bits of matter described? All matter is made up of extremely small particles called atoms. These particles are too small to be seen directly, even under a microscope. The atom is composed of even smaller particles called protons, neutrons, and electrons. The protons and neutrons are located in the dense nucleus of the atom. The electrons surround the nucleus. Protons are positively charged, neutrons have no charge, and electrons are negatively charged.

Wrap Up (cont.) Science is theoretical and dynamic. Models and theories are continually being revised or replaced with new models and theories as new evidence is gathered.

Check-in Here is a model of a carbon atom. 1. List two things this model tells you about the carbon atom. 2. List something this model does not tell you about the carbon atom.

Lesson 12: Atoms By Numbers Atomic Number and Atomic Mass

Lesson 12: Atoms By Numbers ChemCatalyst Models of a helium atom and a beryllium atom are shown. The nucleus of each contains protons and neutrons. The electrons orbit the nucleus. 1. Compare the two models. List three similarities and three differences. 2. Based on the models, why do you think helium is number 2 (the second element) and beryllium number 4 (the fourth element) on the periodic table?

Key Question How are the atoms of one element different from those of another element?

You will be able to: distinguish between atomic number, mass of an atom, and average atomic mass describe the structure of an atom and draw a simple atomic model of an atom extract information from the periodic table related to atomic structure and atomic mass

Prepare for the Activity Work in groups.

Discussion Notes The atomic number of an element is the same as the number of protons in the nucleus of that element. Atomic number = number of protons and electrons in neutral atom (big blue #) Protons and neutrons make up most of the mass of atom. mass of proton and neutron =1 atomic mass unit = 1 amu. Mass number = # of protons + # of neutrons Mass of e- considered negligible

Discussion Notes (cont.) Each successive element has one more proton than the element preceding it. # of neutrons = atomic mass - # of protons (round to whole #) If the # of protons changes, the identity of the atom changes.

Discussion Notes (cont.) The atomic mass of an atom determined by summing the number of protons and neutrons is not identical to the average atomic mass of the element given in the periodic table.

Wrap Up How are the atoms of one element different from those of another element? Each element in the periodic table has one more proton than the element preceding it. The atomic number of an element is the same as the number of protons in the nucleus of each of its atoms.

Wrap Up (cont.) In a neutral atom, the number of electrons is equal to the number of protons. The mass of a proton is 1 atomic mass unit (1 amu). The mass of a neutron is also 1 amu. The mass of an electron is so small it is considered negligible. So the mass of an atom in atomic mass units is simply the sum of the number of protons and the number of neutrons.

Check-in Use your periodic table to identify these elements. 1.Atomic number is Has three electrons when atoms are neutral. 3.Atomic mass is 16.0.

Lesson 13: Subatomic Heavyweights Isotopes

Lesson 13: Subatomic Heavyweights ChemCatalyst A chemist investigating a sample of lithium found that some lithium atoms have a lower mass than other lithium atoms. The chemist drew models of the two different types of lithium atoms, as shown on the following slide.

Lesson 13: Subatomic Heavyweights ChemCatalyst (cont.) 1.What is different about the two atoms? 2.What is the atomic number of each atom? 3.What is the atomic mass of each atom?

Key Question How can atoms of the same element be different?

You will be able to: define isotope and write and interpret the symbol for a specific isotope determine the average atomic mass of an element based on the natural abundance of isotopes of that element predict the number of protons, neutrons, and electrons in the most abundant isotope of an atom, based on average atomic mass

Prepare for the Activity Work in pairs.

Discussion Notes isotopes = atoms of the same element that have different numbers of neutrons Atomic mass units (amu) = “invented” measurement units of atomic mass. The weights of parts of the atom in grams are: Proton = 1.67x Neutron = 1.67x Electron = 9.05x The weights of parts of the atom in amu are: p + = 1.0 amu n 0 = 1.0 amu e - = 0.0 amu

boron atom # protons # neutrons # electrons

Discussion Notes (cont.) Symbols Associated with Isotopes

Discussion Notes (cont.) Isotopes are referred to by their mass numbers. Example: argon-40 (# 40 = mass number) The percentage of each isotope of an element that occurs in nature is called the natural percent abundance of the isotope.

Discussion Notes (cont.) Calculate the Atomic Mass of Neon

Discussion Notes (cont.) Atomic Weight is the average mass of all of the element’s isotopes There is a specific way to symbolize isotopes. Superscript # (on top) = mass # Mass # = protons + neutrons Subscript # (on bottom) = atomic # Atomic # = protons, electrons

Examples Find the # of protons, neutrons, and electrons in each isotope C Cu 3.hydrogen – 2 4.neon - 20

Wrap Up How can atoms of the same element be different? Isotopes of an element have the same number of protons and electrons but different numbers of neutrons. The average atomic mass of an element listed in the periodic table is the weighted average mass of the naturally occurring isotopes of that element. Isotopes are referred to by their mass numbers, as in carbon-12.

Check-in Nitrogen has two naturally occurring isotopes. Predict the number of neutrons in the two isotopes of nitrogen, N. Which isotope do you predict to be more abundant? How do you know?

Lesson 14: Isotopia Stable and Radioactive Isotopes

Lesson 14: Isotopia ChemCatalyst Which of the following are isotopes of copper, Cu? Explain your reasoning. A. CuB. Au C. Cu D. CuE. CuF. Cu

Key Question What types of isotopes do the various elements have?

You will be able to: interpret a graph of naturally occurring isotopes describe the general nuclear composition of a stable nucleus differentiate between a stable isotope and a radioactive isotope

Prepare for the Activity Work in pairs. You should each have a copy of the periodic table.

Discussion Notes The graph of naturally occurring isotopes gives us an idea of how many different isotopes of the elements are found in nature. The words atom, isotope, and element are interrelated. Nearly all atoms have at least one neutron for every proton in the nucleus.

Discussion Notes (cont.) Many isotopes have more neutrons than protons. A handful of the isotopes on the chart are unstable - nucleus breaks apart over time or decays = radioactive Some elements have a naturally occurring radioactive isotope. The isotopes of the elements after bismuth (84 and up) are all radioactive. Radioactive elements emit radiation = rays and particles that break off of nucleus

Discussion Notes (cont.) Radioactive isotope: Any isotope that has an unstable nucleus and decays over time.

Wrap Up What types of isotopes do the various elements have? elements found in nature have between 1-10 isotopes. The neutron-to-proton ratio is an important factor in determining the stability of an isotope. Atoms with small masses have neutron-to-proton ratios of about 1:1. The most massive atoms have neutron-to-proton ratios of about 3:2. Strong nuclear force: force holding positive protons in nucleus Some elements have isotopes that are radioactive. The nuclei of radioactive isotopes are unstable and decay over time.

Check-in 1.Use the chart to determine how many neutrons you would need to make a stable element with 79 protons. 2. What element is this? Write its isotope symbol.

Lesson 15: Nuclear Quest Nuclear Reactions

Lesson 15: Nuclear Quest ChemCatalyst Using the Nuclear Quest game, find the ten kinds of cards shown below. Which cards cause the nucleus of one element to change into the nucleus of a different element?

Key Question What are nuclear reactions?

You will be able to: explain the different processes involved in nuclear changes and the conditions required for those processes explain the connection between nuclear changes and changes in atomic identity

Prepare for the Activity Work in groups of four. The goal of the game is to discover element 112 and name it. This is accomplished by moving the nucleus through the entire periodic table.

Discussion Notes Alpha Decay

Discussion Notes (cont.) Beta Decay

Discussion Notes (cont.) Nuclear chemistry = study of changes to the nucleus. Nuclear reaction: process that involves changes to nucleus. Radioactive decay: spontaneous process - atom emits radiation or particle from nucleus to become more stable Fusion: joining of two nuclei to form larger nucleus and a release of energy Fission: splitting apart of an atomic nucleus into two smaller nuclei and a release of energy (gamma ray)

Discussion Notes (cont.) Nuclear changes frequently involve the transfer of large amounts of energy Alpha decay: nuclear reaction - atom emits an alpha particle ( 4 2 He) atomic number decreases by 2, and mass number decreases by 4 Beta decay: nuclear reaction - neutron changes into a proton, and atom emits beta particle ( 0 -1 e) atomic number increases by 1 Gamma ray: high-energy electromagnetic radiation emitted during nuclear reactions

Wrap Up What are nuclear reactions? Alpha decay results in a decrease in the atomic number by 2. Beta decay results in an increase in the atomic number by 1. Gamma radiation usually accompanies alpha and beta decay and also fission. Gamma radiation can be quite harmful to humans.

Wrap Up (cont.) Nuclear fission involves a single nucleus breaking apart into two smaller nuclei. Nuclear fusion involves two nuclei combining to form a nucleus with a larger atomic number. Nuclear fusion takes place in extremely hot environments, such as the cores of stars.

Lesson 16: Old Gold Formation of Elements

Lesson 16: Old Gold ChemCatalyst 1. What patterns do you notice in the fusion reactions? 2. Do you think gold can be created on Earth by a fusion reaction? Explain your thinking.

Key Question How are new elements formed?

You will be able to: explain how different elements are formed through nuclear reactions write a balanced nuclear equation describe the mechanism behind a nuclear chain reaction

Prepare for the Activity Work individually. You will need a copy of the periodic table and the isotope chart from Lesson 14.

Nuclear processes can be written as nuclear equations. Ca Sc   + U Th  +  Beta particle Alpha particle Discussion Notes

Discussion Notes (cont.) Fission = nucleus breaking up into smaller nuclei. Nuclear reactions change the identity of an element. Starting isotope = parent isotope Resulting isotope = daughter isotope Nuclear fusion = produces bigger (heavier) elements from smaller (lighter) ones.

NameParticleI. D.Charge Penetrating Ability alpha beta gamma

Examples 1.Write the nuclear equation for the alpha decay of bismuth Write the nuclear equation for the beta decay of actinium-227

Discussion Notes (cont.) Nuclear fission releases enormous amounts of energy. Nuclear fission can result in a nuclear chain reaction that produces a great deal of energy. The energy released can be calculated using the equation: E = mc 2

Discussion Notes (cont.) Nuclear Chain Reactions

Wrap Up How are new elements formed? Radioactive decay, fusion, and fission all result in the creation of new elements. The mass of a nucleus changes when neutrons or protons are added or lost. The identity of an element changes when its nucleus gains or loses protons.

Wrap Up (cont.) Radioactive decay happens in the natural world around us. Fission can be spontaneous for unstable nuclei, or it can be provoked using nuclear bombardment and other methods. Fusion of nuclei to form different isotopes happens in the stars.

Check-in In a paragraph, defend this statement: If you want to find gold, your best bet is to dig “old” gold out of the ground. Your chances of making “new” gold are slim.