Professor Lynn Cominsky Joanne del Corral Al Janulaw Michelle Curtis July 3, 2003 The Atom’s...

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Professor Lynn CominskyJoanne del Corral

Al JanulawMichelle Curtis

July 3, 2003

The Atom’s Family

NBSP Physical Science Leadership Institute

7/3/2003 Prof. Lynn Cominsky 2

Standard Connections Students know that all matter is made of

small particles called atoms, too small to see with the naked eye (3)

Students know that all matter is made of atoms…(5)

Students know that each element is made of one kind of atom… (5)

Some questions about the atom What is an atom? What are the parts of an atom? How do we “see” the parts of the atom? What is the structure of the atom? Students know the structure of the atom,

and know it is composed of protons, neutrons and electrons (8)

Atoms – the historical view Students know people once thought that earth,

wind, fire and water were the basic elements that made up all matter (3)

The Greek Empedocle (around 492-432 BC.) divided matter into four elements, that he also called "roots": earth, air, fire and water

The word "atom" comes from the greek "a-tomos" and signifies "indivisible". This notion was invented by Leucippe of Milet in 420 BC

Atoms – the historical view

From 1000-1869, about 50 additional elements were discovered, many by alchemists, including As, Zn, P, Pt, Ni, N, O, Cl and Al.

In ancient times, many elements were known, including C, S, Cu, Ag, Au, Fe, Sn, Sb and Pb. The names of most of these are from the Latin words.

History (continued) Mendeleyev’s periodic table (1869)

classified and sorted elements based on common chemical properties. His table had 62 known elements, and left space for 20 elements that were not yet discovered. The elements were arranged in order of atomic number.

History (continued) The electron was discovered in 1897 by

Thomson. He imagined the atom as a “raisin pudding” with electrons stuck in a cake of positive charge

In 1912, Rutherford discovered the nucleus by doing scattering experiments. He concluded the atom was mostly empty space, with a large dense body at the center, and electrons which orbited the nucleus like planets orbit the Sun

History (continued) Rutherford also realized that the nucleus must

contain both neutral and positively charged particles. The neutron was then discovered in 1932 by Chadwick.

First activity – Rutherford revisited Given: a large wooden board, a mystery shape and

marbles Try to identify the shape that is hiding under the

wooden board. You can only roll marbles against the hidden object and observe the deflected paths that the marbles take. Take at least five minutes to "observe" a shape. Then do a second shape.

Place a piece of paper under the board for sketching the paths of the marbles. Then analyze this information to determine the object's actual shape.

Rutherford activity analysis Black vertical line shows

path of incoming marble Red line shows path of

outgoing marble Green dotted line bisects

the angle made by the incoming and outgoing lines

Reflecting surface is perpendicular to bisecting line

Questions about Rutherford activity Draw a small picture of each shape you studied in

your lab notebook. Can you tell the size of the object as well as its

shape? How could you find out whether the shape has

features that are small compared to the size of your marbles?

Without looking, how can you be sure of your conclusions?

What Rutherford really did Rutherford shot alpha-particles (Helium nuclei) at

a thin gold foil. He found that most went right through. However, some were deflected, and a percentage of those bounced right back at him! He said that “it was like firing a cannonball at tissue paper, and having it ricochet off!”

Can you see how he concluded that the nucleus was a hard small sphere, and that most of the atom was empty space? (As opposed to a plum pudding?)

Vocabulary Electron: negatively charged fundamental

particle Proton: positively charged fundamental

particle Neutron: uncharged fundamental particle Nucleus: small, central unit in the atom that

contains neutrons and protons Atom: smallest unit of an

element

ELD Activities: Analogies, Imagery and Student Involvement

Rutherford simplified -- Have a small group of students (5-6) represent an atomic nucleus, by standing in a circle facing outward.

Have the rest of the students stand around at random spots, to represent the alpha particles.

Assign these students a straight path - either toward the circle or missing it.

If they bump into the circle, they should turn around and the children in the circle gently push them back to where they came from.

Some will bounce back and some will keep going.

Publisher’s Materials

Take some time to look through the state-adopted texts to find activities relating to atoms that could be used in your classroom.

Break – some things to think about

We all know that “opposites attract” and “like charges repel” –SO:

If electrons are negatively charged and protons are positively charged, why don’t the electrons fall into the nucleus?

Standard connections Science experiments show that there are

more than 100 different types of atoms, which are presented in the periodic table of the elements (3)

Students know that the elements are organized in the periodic table by their chemical properties (5)

Students know how to use the periodic table to identify elements in simple compounds (8)

Some questions: What is an element? Why are nuclei and atoms stable? What is a molecule?

http://www.caffeinearchive.com/images/molecule.gif

Key Concepts and Vocabulary: Atoms, Elements and Molecules Atom: smallest unit of an element Element: any of more than 100 fundamental

substances that consist of atoms of only one kind Molecule: a collection of atoms, bound together.

Molecules can be made from only one element, such as H2 or O2

Molecules can be made from different elements, such as H2O or CO2

Parts of an Atom

Each element in the Periodic Table has a different number of protons in its nucleus Protons have positive charge Change the number of protons change elements This is called nuclear physics

The element also has the same number of electrons Electrons have negative charge Change the number of electrons ionize the element This is called chemistry

Some elements also have neutrons Neutrons have no charge They are in the nuclei of atoms

The Hydrogen Atom

• One electron orbiting a nucleus

• 1 proton = Z = atomic number

• 0 neutrons = N

• Total mass = A = Z+N =1

• Singly ionized Hydrogen is missing one electron = 1H+

• Add a neutron and you have Deuterium = 2H = D

The Helium Atom

• Two electrons orbiting a nucleus

• 2 protons = Z = atomic number

• 2 neutrons = N

• Total mass = A = Z+N =4

• Singly ionized Helium is missing one electron = 4He+

• Doubly ionized Helium is missing both electrons = particle = 4He++

If Helium loses one of its protons (and one of its electrons), it becomes a different element

Isotopes and Elements

If Helium loses one of its neutrons, it becomes an isotope

e3H (Tritium)

History of the atom (Part 2) Following Rutherford’s planetary model of the

atom, it was realized that the attraction between the electrons and the protons should make the atom unstable

Bohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special quantized locations

History of the atom (continued) In the Bohr model, the electron can

change orbits, accompanied by the absorption or emission of a photon of a specific color of light.

History of the atom (continued) Modern quantum theories lead to stable

locations of electrons, which are not exact planetary orbits, but are characterized by specific quantum numbers.

Each electron shell is characterized by a different principle quantum number, usually called n.

History of the atom (continued) In quantum theory, the

electron shells are not fixed orbits, but clouds of probability. You can’t measure the exact location of the electron.

Each electron orbital has a different shape, and no two electrons can be in the same orbital (unless they have opposite spins.)

History of the atom (continued) The quantum rules for

the electron orbitals in an atom determine the row structure in the periodic table.

The geometry of the electron orbitals determines the structure of an atom

History of the atom (continued): The spin of the electron is another quantum

property. In the planetary model, it is similar to the spin of the Earth on its axis. There are two choices for the orientation of the electron’s spin axis: up or down.

Some further questions: What is periodic about the periodic table? What types of chemical properties are used

to classify the elements?

ELD Activity: Visual Imagery and Identifying elements Make a list of all the element names that

you know (e.g., Carbon, Oxygen, Silicon) What are some of the common household

items that contain these elements? Draw a picture of the items

Element Item Drawing

Lunch puzzler How do nuclei stay together when they are

filled with positive charges?

Periodic Table of the ElementsReview: What are the numbers in each box?

Navigating the Periodic Table The rows are the “periods”

Each period starts a new shell of electrons The periods are numbered starting with 1 at

the top

The columns are the “groups” Each group has similar chemical properties The groups are numbered starting with 1 at

the left Elements with similar properties have the

same number of electrons in the outermost shell

Electron shells and atomic structure

The first shell will hold up to two electrons. The orbital is spherical, and called 1s. The first row of the periodic table consists of 2 elements with 1s electrons.

The second (and third) rows each add eight electrons. The shells that are filled are made of a spherical orbital that holds 2 electrons, called 2s or 3s, and 3 non-spherical orbitals that hold a total 6 electrons, called 2p or 3p.

In the fourth row of the periodic table, the 4s orbital fills first, then a new orbital, 3d, begins to be filled. It can hold 10 electrons.

p-orbitals

What orbital is being filled in row 4 after 3d is filled?

What is the pattern that repeats in row 5?

d-orbitals

Electron shells and atomic structure In row 6, a new type of orbital, 4f, appears in between elements 57 and 72. All the

elements with 4f electrons have very similar chemical properties. They are known as the Lanthanides (after element Z=57, Lanthanum) or rare earths.

A similar pattern repeats in row 7, with the 5f orbitals filling between elements 89 and 104. These elements also have similar chemical properties, and are called the Actinide elements (after element Z=89, Actinium).

There are 7 different f-orbitals: each can hold 2 electrons for a total of 14 in the 4f or 5f orbitals.

Third activity: Shell structure Carbon=C Sodium=Na Neon=Ne Chlorine=Cl

How many protons and electrons do these elements have?

Draw the electron shell structure for each.

Review: what is this element?

Shell structure: thinking deeper Where are the elements with very stable outer

shells in the periodic table? What do we call them?

Where are the elements with one electron outside a filled shell?

Where are the elements that need one electron to fill their shells?

What happens when these two types of elements are combined chemically?

So, what are some rules for making molecules?

Key concepts: Periodic Table The number of elements in each of the horizontal

rows (periods) in the periodic table, are due to the quantum rules that govern the electron orbitals.

In vertical columns (groups) in the periodic table, similar chemical properties are due to the number of electrons in filled or unfilled shells.

Completely filled shells make an atom very stable Elements with 1 or 2 electrons outside of filled

shells or with 1 or 2 missing electrons are very chemically reactive. They always try to combine with other elements that can fill their shells.

Vocabulary Atomic number: the number of protons in

the nucleus of an element Atomic mass: the total mass in one atom of

an element Ionization: removal of electrons from an

atom Quantum: a very small discrete unit of light

or energy

ELD Activities:Academic Language What is meant by the phrase quantum leap? Is this phrase consistent with the scientific

definition of the word quantum?

ELD Activities:Visual Imagery Use modeling clay to represent atomic

structure. Use different colors for protons, neutrons and electrons. Have the students try different combinations for different elements

Publisher’s Materials

Take some time to look through the state-adopted texts to find activities relating to the periodic table that could be used in your classroom.

Examples: HC p. C46

Thinking deeper: The forces in the atom Electrons are bound to nucleus by

the Coulomb (electromagnetic) force

Protons in nucleus are held together by the strong nuclear force

Neutrons can decay into protons by weak nuclear force, emitting an electron and an anti-neutrino. The weak force is also responsible for radioactivity.

F = k q1 q2

n = p + e +

Thinking deeper: The forces in the atom

Gravity and the electromagnetic forces both have infinite range but gravity is 1036 times weaker at a given distance

The strong and weak forces are both short range forces (<10-14 m)

The weak force is 10-8 times weaker than the strong force within the nucleus

There are four fundamental forces in physics.

Standard connections Students know metals have properties in

common, such as high electrical conductivity (5)

The organization of the periodic table is based on the properties of the elements and reflects the structure of atoms. Students know how to identify regions corresponding to metals, nonmetals and inert gases (8)

Fourth Activity: Electrical conduction

How can we tell which elements are good electrical conductors?

Are all metals good conductors? Are all good conductors metals? How can we tell which materials are good

electrical insulators? How do you think the electrons in

conductors differ from those in insulators?

Equipment for Electrical Conduction activity

Insulated wires Batteries Bulbs Other things like rubber, wood, glass,

plastic, aluminum, paper clips, etc. Masking tape

More questions for Electrical Conduction activity

Were you surprised by the some of the items that were conductors?

Were you surprised by some of the items that were insulators?

What did the conductors have in common? What did the insulators have in common?

Electrical Conductors: A deeper look The best conductors are Copper (Cu), Silver

(Ag) and Gold (Au) Cu has Z=29, Ag has Z=47 and Au has Z=79 How are these electrons arranged?

29 = 2+8+8+10+1

47 = 2+8+8+18+10+1

So, why are these elements good conductors?

79 = 2+8+8+18 + 18+14+10 +1

Key concepts: Electrical Conductors Conductors are usually (but not always) metals – they

have electrons that move easily, as they are outside filled shells

Insulators are materials that block the flow of electrons. They do not have easily removed electrons.

Metals occur where the d-orbitals are being filled in the periodic table.

When you flip the switch, individual electrons do not instantaneously move through the entire length of the wire. Rather, they quickly bump into the metal nuclei, as they slowly drift down the wire (at about 0.5 mm/sec)

Vocabulary Conductor: material that allows the flow of

electricity

Insulator: material that blocks the flow of electricity

ELD Activities: Academic Language Writing and talking aloud help the students to

better process information: The person who leads an orchestra or a band is

called a conductor. How is an orchestra conductor similar to an electrical conductor?

Buildings stay warm because of insulation material. How is insulation material similar to electrical insulators?

Share your ideas and opinion with a partner and write it in your journals in your own words.

Reading connections Read this article for students about the

discovery of the electron. Read the longer article at home over the

weekend. Reading strategy:

Text to text Text to self Text to world

Takeaway – fireworks puzzler What is the science behind the different

colors that you see when you watch the July 4 fireworks?

Lesson Study Activities

Identify a key concept from today’s lecture for further development

Review the publisher’s materials about this key concept

Think about the best way to present this key concept in your classroom

Resources

http://chemicool.com/ http://www.ill.fr/dif/3D-crystals/magnets.html http://perso.club-internet.fr/molaire1/e_histoire.html http://www.shodor.org/chemviz/ orbitals/sorbital.gif http://members.aol.com/ChangChem/porbital.gif http://members.aol.com/ChangChem/dorbital.gif Physics by Inquiry – L. McDermott and the PEG at U

Washington http://www.slac.stanford.edu/pubs/beamline/27/1/27-1-pais.pdf http://www.cc.oulu.fi/~kempmp/colours.html

Professor Lynn Cominsky Joanne del Corral Al Janulaw Michelle Curtis July 3, 2003 The Atom’s...

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