Introduction to Atoms 8th Grade Science © Fall 2005, Pflugerville ISD, 8th Grade

Who helped Develop the Atomic Theory? What Do You Think? Imagine that you have cut a penny in half. Then, you take one piece and half it again. Will this continue forever, or will you come to a point where no more cutting is possible? Unit A : Chapter 2

*Who helped Develop the Atomic Theory? List one contribution of each scientist. Democritus (400 BC) Dalton (1766- 1844) Thompson (1856- 1940) Rutherford (1871- 1937) Bohr (1885- 1962) Unit A : Chapter 2

Who helped Develop the Atomic Theory? Democritus was a Greek philosopher who theorized that all matter was made of invisible particles called atoms. Democritus of Abdera, about 460-370 BCE Unit A : Chapter 2

Who helped Develop the Atomic Theory? Dalton, a British chemist and teacher, theorized that all elements are made up of the same type of atom and that these atoms combine in specific proportions to form compounds. John Dalton 1766-1844 Unit A : Chapter 2

Who helped Develop the Atomic Theory? Thomson received the Nobel Prize in physics in 1906 for his discovery of the electron. Joseph John “J.J.” Thomson 1856-1940 Unit A : Chapter 2

*Who helped Develop the Atomic Theory? Rutherford, a former student of Thomson’s from New Zealand, discovered that an atom contains mostly space and that it has a small positively charged nucleus. Ernest Rutherford 1871- 1937 Unit A : Chapter 2

Who helped Develop the Atomic Theory? He expected his alpha particles to go straight through the foil, and most of them did. But some of the particles were deflected or bounced straight back! This showed that a nucleus with a positive charge makes up the center of an atom. Rutherford’s Gold Foil Experiment Unit A : Chapter 2

Who helped Develop the Atomic Theory? Bohr described the motion of electrons around the nucleus. Niels Bohr 1885-1962 Unit A : Chapter 2

Who helped Develop the Atomic Theory? Bohr said that electrons orbit the nucleus at specific energy levels, and can move from one level to another. Bohr’s Atomic Model Unit A : Chapter 2

Who helped Develop the Atomic Theory? James Chadwick was awarded the Nobel Prize in Physics in 1932 for his discovery of the neutron. His discovery helped explain the mass of the atom and was instrumental in the development of the atomic bomb. James Chadwick (1932) Unit A : Chapter 2

Development of the Atomic Theory The Modern Atomic Model states that there are regions inside an atom where electrons are likely to be found. These regions are called electron clouds. Electron Cloud Model Unit A : Chapter 2

The Atom What Do You Think? What is the smallest thing you have ever seen? How does it compare to the size of an atom? Unit A : Chapter 2

*What are the parts of the Atom? The nucleus is the small, dense, positively charged center of the atom. Protons are positively charged particles in the nucleus Neutrons are particles in the nucleus that have no charge Electrons are negatively charged particles which orbit the nucleus. Nucleus Unit A : Chapter 2

The Atom What Do You Think? What are some differences you use to tell one of your classmates from another? Unit A : Chapter 2

*What does the information in the box tell me? 2 He 4.008 Atomic Number = # of protons Elemental Symbol Atomic Mass = # of protons plus neutrons 16

Atomic Number- the Number of Protons The Helium atom has two protons in its nucleus. This means that it has the atomic number 2. Helium Atom Unit A : Chapter 2

Atomic Number- the Number of Protons The Lithium atom has three protons in its nucleus. This means that it has the atomic number 3. Lithium Atom Unit A : Chapter 2

Atomic Mass Number- Protons plus Neutrons The Helium atom has two protons and two neutrons in its nucleus. This means that it has the atomic mass number 4. Helium Atom Unit A : Chapter 2

Atomic Mass Number- Protons plus Neutrons The Lithium atom has three protons and four neutrons in its nucleus. This means that it has the atomic mass number 7. Lithium Atom Unit A : Chapter 2

*What are Isotopes? Notice that these isotopes of hydrogen have the same number of protons, but different numbers of neutrons. Isotopes of Hydrogen Unit A : Chapter 2

Atomic Mass Number- Isotopes These isotopes are also known as Hydrogen-1, Hydrogen-2, and Hydrogen-3 Unit A : Chapter 2

3-2-1 Summarize!!! Write 3 facts you wrote in your notes in complete sentences. Write 2 facts given to you verbally that you did NOT write down in complete sentences. Write 1 question that presented itself to you while taking notes.

Let’s Review! - 1 - In the history of science, what are some ways scientists have described the atom? Unit A : Chapter 2

What are the parts of an atom, and how is an atom structured? Let’s Review! 2 - What are the parts of an atom, and how is an atom structured? Unit A : Chapter 2

Let’s Review! 3 - What is the atomic number of an atom? How is this different from the atomic mass number? Unit A : Chapter 2

Atomic Theory Web Sites to Visit http://education.jlab.org/qa/history_02.html http://www.chemheritage.org/EducationalServices/chemach/ppt/jd.html http://www.aip.org/history/electron/jjhome.htm http://www.chemheritage.org/EducationalServices/chemach/ans/er.html http://nobelprize.org/physics/laureates/1922/bohr-bio.html Unit A : Chapter 2