Chapter 18: Properties of Atoms and the Periodic Table

Section 1: Structure of the Atom

http://61.19.145.8/student/m5year2006-2/502/group11/periodic_table.gif

http://www.privatehand.com/flash/elements.html

http://www.youtube.com/watch?v=d0zION8xjbM

Atoms and Elements• Elements are abbreviated in scientific

shorthand – first letter or two of element’s name

• Atom – smallest piece of matter that still has the properties of the element– Protons have an electrical charge of 1+.– Neutrons do not have an electrical charge.– Electrons have an electrical charge of 1-– Protons and neutrons are in the nucleus of an

atom; electrons surround the nucleus

Model of the Atom

http://www.csmate.colostate.edu/cltw/cohortpages/viney_off/atom.jpg

Quarks• Protons and neutrons make up most

of the mass in matter

• They are made up of smaller particles called quarks.– Quarks are studied by colliding accelerated

charged particles with protons, which leave tracks in a bubble chamber.

• Six quarks are known to exist, but protons and neutrons are composed of up and down quarks

Meet the Quarks

http://www.jlab.org/~hleiqawi/6quarks.jpg

Up, Down, Top, Bottom, Strange, and Charm

Models: Tools for Scientists• Scientists use scaled-up models to

represent atoms.

• Atoms are so tiny, not even the most powerful microscope can see them--that means we have NEVER seen an atom!

• Current electron cloud model shows electrons traveling in specific energy levels around a nucleus of protons and neutrons. So how do we know this?

• Models have evolved over thousands of years using scientific evidence.

Electron Cloud Model of the Atom

http://www.csmate.colostate.edu/cltw/cohortpages/viney_off/atom.jpg

Models of Atoms: A History

1. Democritus’s Uncuttable Atom

http://web.mit.edu/philos/www/mm/democritus.jpg

• Ancient Greek philosopher (400 B.C.)

• Proposed elements are composed of tiny solid particles that could not be further divided

Models of Atoms: A History

1. Democritus’s Uncuttable Atom• Particles were

called “atomos,” meaning “uncuttable”

http://www.phys.unsw.edu.au/hsc/hsc/pics/1.gif

Models of Atoms: A History

2.John Dalton’s Billiard Ball

http://chemreview.pbwiki.com/f/image.jpg

• English Physicist (1800)

• Proposed elements are composed of tiny solid spheres

http://darkwing.uoregon.edu/~ch111/images/democritus.gif

Models of Atoms: A History

3. J.J. Thomson’s Cookie Dough

http://upload.wikimedia.org/wikipedia/commons/c/c1/J.J_Thomson.jpg

• English Physicist (1904)

• Negatively charged particles are evenly distributed within a positively charged solid sphere

Models of Atoms: A History

3. J.J. Thomson’s Cookie DoughThe + matter is the dough; the – matter

are the chocolate chips

Models of Atoms: A History

4. Ernest Rutherford’s Massive Nucleus

http://www.wpclipart.com/famous/science/Ernest_Rutherford.png

• English Physicist (1911)

• Most of the mass of the atom is in the positive nucleus; electrons surround nucleus; empty space in between

Models of Atoms: A History

4. Rutherford’s Gold Foil Experiment

Models of Atoms: A History

5. Niels Bohr’s Fixed Orbits• Danish Physicist

(1913)

• Electrons travel in fixed orbits, or certain paths, around the nucleus

http://astro.schoolnet.ir/astro%20persian%20ver/images/Niels_Bohr.jpg

Models of Atoms: A History

5. Niels Bohr’s Fixed Orbits• Electrons have

energy levels

• Electrons with more energy are farther from the nucleus

http://www.splung.com/nuclear/images/atoms10.gif

Models of Atoms: A History

6. Electron Cloud Model (1920)• Electrons do not

travel in fixed orbits

• Electrons are randomly found in an area around the nucleus

• Currently accepted model

http://universe-review.ca/I15-53-quantum.jpg

Models of Atoms: A History

7. James Chadwick’s Neutrons• English Physicist

(1932)

• Presence of neutral neutrons in the nucleus, in addition to the protons

http://www.aps.org/publications/apsnews/200705/images/chadwick_web.jpg

Review Questions, p. 549 1-4Answer these questions:

1. Write the chemical symbols for the elements carbon, aluminum, hydrogen, oxygen, and sodium.

2. What are the names, charges, and locations of 3 kinds of particles that make up an atom?

3. What is the smallest particle of matter? How were they discovered?

4. Describe the electron cloud model of the atom.