1. Chapter 18: Properties of Atoms and the Periodic Table
Section 1: Structure of the Atom

2. 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

3. Model of the Atom

4. 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

5. Up, Down, Top, Bottom, Strange, and Charm
Meet the Quarks
Up, Down, Top, Bottom, Strange, and Charm

6. 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.

7. Electron Cloud Model of the Atom

8. Models of Atoms: A History 1. Democritus’s Uncuttable Atom
Ancient Greek philosopher (400 B.C.)
Proposed elements are composed of tiny solid particles that could not be further divided

9. Models of Atoms: A History 1. Democritus’s Uncuttable Atom
Particles were called “atomos,” meaning “uncuttable”

10. Models of Atoms: A History John Dalton’s Billiard Ball
English Physicist (1800)
Proposed elements are composed of tiny solid spheres

11. Models of Atoms: A History 3. J.J. Thomson’s Cookie Dough
English Physicist (1904)
Negatively charged particles are evenly distributed within a positively charged solid sphere

12. Models of Atoms: A History 3. J.J. Thomson’s Cookie Dough
The + matter is the dough; the – matter are the chocolate chips

13. Models of Atoms: A History 4. Ernest Rutherford’s Massive Nucleus
English Physicist (1911)
Most of the mass of the atom is in the positive nucleus; electrons surround nucleus; empty space in between

14. Models of Atoms: A History 4. Rutherford’s Gold Foil Experiment

15. 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

16. Models of Atoms: A History 5. Niels Bohr’s Fixed Orbits
Electrons have energy levels
Electrons with more energy are farther from the nucleus

17. 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

18. 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

19. Review Questions, p. 549 1-4 Answer these questions:
Write the chemical symbols for the elements carbon, aluminum, hydrogen, oxygen, and sodium.
What are the names, charges, and locations of 3 kinds of particles that make up an atom?
What is the smallest particle of matter? How were they discovered?
Describe the electron cloud model of the atom.