C HAPTER
5 TE Atoms
Chapter Outline
5.1 CHAPTER5: ATOMS
5.1. Chapter 5: Atoms www.ck12.org
5.1 Chapter 5: Atoms
Chapter Overview
An atom consists of protons, neutrons, and electrons; and protons and neutrons consist of quarks. The strong force and electric force hold the atom together. An atom can be characterized by its atomic number and mass number. The history of the atom began with Democritus and included major contributions by Dalton, Thomson, Rutherford, and Bohr. Modern ideas about the atom include energy levels, orbitals, and electron clouds.
Online Resources
See the following Web sites for appropriate laboratory activities:
This active lab is an entertaining way for students to explore atomic structure and other concepts introduced in Lesson 5.1. It uses simple materials such as laundry baskets and colored balls and does not require a science lab.
You can divide the class into two teams and have them compete to do the activity with the fewest mistakes in the least amount of time. The URL provides complete instructions, extensions, assessments, diagrams, and an answer key.
• http://www.middleschoolscience.com/atomicmusicalchairs.pdf
The lab “Electron Probability” at the URL below is a creative way to help students understand probability distribu- tions of electrons in the electron cloud model of the atom (Lesson 5.3).
• [mrsj.exofire.net/chem/docs/eprob_lab.doc mrsj.exofire.net/chem/docs/eprob_lab.doc]
These Web sites may also be helpful:
The URL below has links to several sites that offer information, lesson plans, simulations, hands-on activities, and online quizzes about atoms.
• http://ethemes.missouri.edu/themes/574
When you teach Lesson 5.2, students may benefit from the overview of atomic history at the following URL. It includes review questions, a summary, and exercises so students can check their comprehension.
• http://www.absorblearning.com/chemistry/demo/units/LR301.html#Exercises
For background information on modern atomic theory in Lesson 5.3, these URLs may be useful:
• http://en.wikipedia.org/wiki/Atomic_orbital
• http://www.chemguide.co.uk/atoms/properties/atomorbs.html
• http://www.chem.purdue.edu/gchelp/aos/whatis.html
• http://www.chm.davidson.edu/vce/atomicorbitals/index.html
Pacing the Lessons
T
ABLE5.1:
Pacing the LessonsLesson Class Period(s) (60 min)
5.1 Inside the Atom 2.0
5.2 History of the Atom 2.0
5.3 Modern Atomic Theory 2.0
5.2. Lesson 5.1 Inside the Atom www.ck12.org
5.2 Lesson 5.1 Inside the Atom
Key Concept
The nucleus of an atom contains positive protons and neutral neutrons, which are held together by the strong force.
Protons and neutrons consist of even smaller particles called quarks, which are held together by gluons. Negative electrons constantly move around the nucleus because of the attraction of opposite electric charges. The number of protons in an atom is the atomic number, which is unique for each element. The number of protons plus neutrons is the mass number, which equals the atom’s mass in atomic mass units.
Standards
• SCI.CA.8.PS.3.a; SCI.CA.8.PS.7.b; SCI.AC.8.IE.9.f
• MCR.6-8.SCI.8.1; MCR.6-8.SCI.9.1
• AAAS.6-8.4.D.1, 2; AAAS.6-8.4.G.5; AAAS.6-8.11.B.1, 3; AAAS.6-8.11.D.3
Lesson Objectives
• Compare and contrast protons, neutrons, and electrons.
• Describe the forces that hold the particles of atoms together.
• Define atomic number and mass number.
• Describe ions and isotopes
• Identify the particles called quarks.
Lesson Vocabulary
• atomic mass unit (amu): SI unit for the mass of an atom, where 1 amu equals the mass of a proton (about 1.7 x 10-24 grams)
• atomic number: number of protons in an atom
• electron: negatively charged atomic particle that moves around the nucleus of the atom
• ion: positively or negatively charged particle that forms when an atom gains or loses electrons
• isotope: atom that differs in the number of its neutrons from other atoms of the same element
• mass number: number of protons plus neutrons in an atom; equal to the atom’s mass in atomic mass units (amu)
• neutron: electrically neutral atomic particle inside the nucleus of an atom
• nucleus: tiny region at the center of an atom that contains protons and neutrons and makes up almost all of the atom’s mass
• proton: positively charged atomic particle inside the nucleus of an atom
• quark: type of fundamental particle of matter that makes up protons and neutrons
Teaching Strategies
Introducing the Lesson
Play a word association game with the class to introduce the lesson. Tell students to say whatever word first comes to mind when they hear the word “atom.” (Sample responses might include “matter,” “tiny,” “nucleus,” “molecule,”
“electron,” and “particle.”) The activity will help students recall what they already know about atoms.
Activity
Help students learn the parts of the atom with the Atoms Family worksheet and song at the first URL below. Divide the class into small groups and have each group complete the worksheet. Encourage students to sing the Atoms Family song. Finally, have groups complete the Atoms Family math challenge at the second URL.
• http://sciencespot.net/Media/atomsfam.pdf
• http://sciencespot.net/Media/atomicmath.pdf
Building Science Skills
Stress the importance of using models to study atoms because they are so small. Then have students create models of the atom using one or more ideas suggested at the following URL.
• http://www.proteacher.org/c/457_Atoms_and_Molecules.html
Demonstration
Have students examine the periodic table .You can use the interactive periodic table at the following URL with a projector or TV screen. Focus on one element in the table, such as carbon. Point out its atomic number and atomic mass (atomic weight). Based on these two numbers, have students calculate the number of neutrons in the atom.
• http://www.ptable.com/
Differentiated Instruction
Pair English language learners and native English speakers, and have partners make a cluster diagram centered on the atom. They should add surrounding circles for parts of the atom, atomic forces, atomic number and mass number, ions and isotopes, and quarks. Tell them to add important details to each circle.
Enrichment
Ask students to make a word-search or criss-cross puzzle using lesson vocabulary terms. They can make the puzzle by hand or use the free puzzle maker at the URL below. Distribute copies of their puzzles for other students to solve.
• http://www.discoveryeducation.com/free-puzzlemaker/?CFID=3512110&CFTOKEN=69625103
5.2. Lesson 5.1 Inside the Atom www.ck12.org Science Inquiry
Divide the class into pairs and have partners explore the interactive “Build an Atom” simulation at the URL below.
Students will build an atom with subatomic particles and observe how the element, charge, and mass of the atom change as they add the different particles.
• http://phet.colorado.edu/en/simulation/build-an-atom Common Misconceptions
The URL below lists several common misconceptions that middle schoolers may have about atoms. Use some or all of the misconceptions to create a true-or-false quiz. For any misconceptions that students think are true, explain why they are false.
• http://departments.weber.edu/sciencecenter/7th%20misconceptions.htm
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 5.1 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this lesson, you saw several simple models of atoms. Models are useful for representing things that are very small.
Scientists have used models to represent atoms for more than 200 years. In the next lesson, you’ll read about some of the earlier models.
• How might scientists have modeled atoms before the particles inside atoms were discovered?
• How do you think earlier models might have differed from the models in this lesson?
5.3 Lesson 5.2 History of the Atom
Key Concept
The ancient Greek philosopher Democritus first introduced the idea of the atom. The idea was re-introduced by John Dalton in 1800. He provided evidence for atoms and developed atomic theory. J.J. Thomson discovered electrons and proposed the plum pudding model of the atom. Ernest Rutherford discovered the nucleus and protons and proposed the planetary model of the atom.
Standards
• MCR.6-8.SCI.11.1, 3, 4; MCR.6-8.SCI.13.5
• NSES.5-8.A.2.5, 7; NSES.5-8.G.2.1; NSES.5-8.G.3.3
• AAAS.6-8.1.A.3, 4; AAAS.6-8.1.B.2; AAAS.6-8.4.D.1, 2; AAAS.6-8.10.F.1, 2; AAAS.6-8.11.B.1, 3, 5;
AAAS.6-8.12.D.9
Lesson Objectives
• State Democritus’s ideas about the atom.
• Outline Dalton’s atomic theory.
• Explain how Thomson discovered electrons.
• Describe how Rutherford found the nucleus.
Lesson Vocabulary
No new vocabulary terms are introduced in this lesson.
Teaching Strategies
Introducing the Lesson
Before you teach this lesson, demonstrate to students the thinking behind Democritus’s idea of the atom. As students watch, cut an apple in half. Then cut one of the halves in half. Continue cutting the pieces in half until they are too small to cut into smaller pieces. Relate the demonstration to Democritus’s idea of “uncuttable” pieces, or atomos.
He proposed that matter is made up of tiny particles that cannot be reduced to smaller pieces. Tell students they will learn in this lesson more about Democritus’s idea as well as other early ideas about the atom.
5.3. Lesson 5.2 History of the Atom www.ck12.org Demonstrate
You can demonstrate Dalton’s, Thomson’s, and Rutherford’s atomic models using bowls of gelatin with and without fruit such as berries. Dalton’s model can be represented by a bowl of plain gelatin, Thomson’s by a bowl of gelatin with berries scattered throughout it, and Rutherford’s by a bowl of gelatin with a single berry in the middle. Have students match the bowls of gelatin with the scientists’ models of the atom.
Activity
Have students do the “Rutherford Roller” activity at the following URL. The activity simulates Rutherford’s famous gold-foil experiments in which he deduced the existence of the atomic nucleus from indirect evidence. At the end of the activity, relate it to Rutherford’s experiments.
• http://www.exo.net/~emuller/activities/Rutherford%20Roller.pdf#search=%22Rutherford%20experiment%20w ith%20marbles%22
Discussion
Discuss Dalton’s atomic theory and how well it has withstood the test of time. List the parts of the theory on the board, and ask students which part or parts they think may no longer be accepted (atoms are the smallest particles of matter, which cannot be divided into small particles). Remind students that scientists now know there are particles smaller than the atom, including extremely small particles called quarks.
Differentiated Instruction
Assign the two questions below for students to think about. Then pair any English language learners or less proficient readers with other students, and have partners discuss the questions. Finally, have the students work together to write answers to the questions.
1. Atoms are too small to be seen without special microscopes that were invented in the 1980s, but scientists had already learned a lot about atoms before then. How could scientists learn about atoms without being able to see them?
2. What did early scientists think atoms were like? How did early ideas differ from today’s ideas about atoms?
Enrichment
Students with an interest in history might enjoy researching and creating a timeline of the history of the atom. Tell them to include modern discoveries and ideas as well as the events described in this lesson. They can start with the URLs below. Display their timeline in the classroom and refer to it as you teach this lesson and the next.
• http://www.nobeliefs.com/atom.htm
• http://atomictimeline.net/index.php
• http://www.timetoast.com/timelines/28969
• http://www.visionlearning.com/library/module_viewer.php?mid=50 Science Inquiry
Have students do one or more of the hands-on simulation activities described at the URL below. The simulations will allow them to model how subatomic particles were discovered on the basis of indirect evidence.
• http://mypages.iit.edu/~smile/ch9211.html History Connection
Place the achievements of Ernest Rutherford in historical context. Have students read about the life and discoveries of Ernest Rutherford at one or more of the URLs below. Based on their reading, ask them to identify what they think is Rutherford’s most important scientific contribution. Also ask whether they agree or disagree with a Rutherford biographer’s claim that “Rutherford was one of the most illustrious scientists of all time.”
• http://www.bbc.co.uk/history/historic_figures/rutherford_ernest.shtml
• http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html
• http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structu re/rutherford.aspx
• http://www.aboutnuclear.org/view.cgi?fC=History,Hall_of_Fame,Ernest_Rutherford
• http://www.blupete.com/Literature/Biographies/Science/Rutherford.htm
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 5.2 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this lesson, you read how models of the atom changed as scientists discovered the particles that make up atoms. In the next lesson, you will read how Rutherford’s model was revised as scientists learned even more about electrons.
For example, they discovered that electrons do not travel around the nucleus in random orbits as Rutherford thought.
• Can you predict how electrons might move around the nucleus?
• How might Rutherford’s model be changed to show this?
5.4. Lesson 5.3 Modern Atomic Theory www.ck12.org
5.4 Lesson 5.3 Modern Atomic Theory
Key Concept
Bohr introduced the idea of energy levels, which confine electrons to certain fixed distances from the nucleus.
Today, electrons are represented by an electron cloud model. Denser regions of the cloud, called orbitals, show where electrons are most likely to be.
Standards
• MCR.6-8.SCI.11.3, 4
• NSES.5-8.A.2.5; NSES.5-8.G.2.1
• AAAS.6-8.1.A.3; AAAS.6-8.1.B.2; AAAS.6-8.11.B.1, 3, 5; AAAS.6-8.12.D.9
Lesson Objectives
• Define energy levels.
• Describe the electron cloud and orbitals.
Lesson Vocabulary
• electron cloud: area surrounding the nucleus of an atom where electrons are likely to be
• energy level: area located at a fixed distance from the nucleus of an atom where electrons can orbit the nucleus
• orbital: dense region in the electron cloud around the nucleus of an atom where electrons are most likely to be
Teaching Strategies
Introducing the Lesson
Start a simple sketch of a hydrogen atom on the board by drawing a small circle labeled “nucleus.” Add a smaller circle labeled “proton” inside the nucleus. Call on a student to come to the board and add the electron and its orbit to the sketch. (The student is likely to draw a circle around the nucleus and add a symbol such as a dot for the electron.) Point out that this is how electrons are usually represented but it’s misleading. Explain that if the nucleus were the size of the nucleus in the sketch, then the electron orbit would actually be about half a mile away with nothing but empty space in between. Tell students they will learn more about electrons and where they are located in the atom when they read this lesson.
Using Visuals
Students may confuse energy levels and orbitals. Relate the energy levels in Figure 5.15 to the number of orbitals per energy level in Table 5.1.
Question: If an atom has electrons only in the first energy level, how many orbitals and electrons can it have?
Answer: It can have a maximum of one orbital and two electrons.
Question: If an atom has electrons in just the first two energy levels, how many orbitals and electrons can it have?
Answer: It can have a maximum of six orbitals (one in energy level 1 and four in energy level 2) and a maximum of 12 electrons (2 per orbital).
Discussion
Differentiated Instruction
Have students make a KWL chart for the position of electrons in atoms. Tell them to divide a sheet of paper into three columns and label them from left to right “Know,” “Want to Know,” and “Learned.” Before they start reading, they should fill in the first column with what they already know (e.g., electrons are located outside the nucleus). They should also fill in the second column with questions they still have (e.g., How far from the nucleus are the electrons?).
Tell students to try to find answers to their questions when they read the lesson. Respond to any questions that remain unanswered after they finish reading.
Enrichment
Interested students can dig deeper into orbitals and learn about s, f, p, and other specific orbitals. The URLs below are good sources of information and images. You might want to have them teach the topic to the class. If so, have them use visuals in their presentation.
• http://en.wikipedia.org/wiki/Atomic_orbital
• http://www.chemguide.co.uk/atoms/properties/atomorbs.html
• http://www.d.umn.edu/~pkiprof/ChemWebV2/AOs/index.html
Science Inquiry
Challenge the class to brainstorm how they might create a two- or three-dimensional representation of the electron cloud model. How could they represent the nucleus? The electron cloud? For ideas, students can see animated two-dimensional representations of the electron cloud model at these URLs:
• http://www.regentsprep.org/regents/physics/phys05/catomodel/cloud.htm
• http://www.lionden.com/chemistry_models.htm
Real-World Connection
Relate energy levels to the real world. Virtually all students will be familiar with fluorescent lights. Tell them that the light is energy emitted by electrons jumping from higher to lower energy levels. They can learn more at this URL:http://home.howstuffworks.com/fluorescent-lamp.htm .
5.4. Lesson 5.3 Modern Atomic Theory www.ck12.org
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in theCK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 5.3 Quiz inCK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this chapter, you learned that atoms of each element have a unique number of protons. This is one way that each element differs from all other elements.
• How could the number of protons be used to organize elements?
• If one element has more protons than another element, how do their numbers of electrons compare?
C HAPTER
6 TE Periodic Table
Chapter Outline
6.1 CHAPTER6: PERIODICTABLE