chapter 18: properties of atoms and the periodic table section 1: structure of the atom
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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.
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