The Atomic Nature of Matter

1. The AtomicNature of Matter An overview of the inner-cosmos Physics 1100, Fall 2011

2. The Search for Basic Constituents Traces Back to Greek Times • Atomic Hypothesis from Democritus • How many “basic” constituents should we expect? • Air • Fire • Earth • Water Say the Greeks Physics 1100, Fall 2011

3. Atoms make up the everyday material world • Everything is made of atoms! • Crystalline arrays – solids • Loose atoms rattling around – gases • Sloppy arrangements of atoms – liquids Physics 1100, Fall 2011

4. Physics 1100, Fall 2011

5. Atoms Are Composite Objects • Protons (+ electric charge), p • Electrons (– electric charge), e • Neutrons (no charge), n • Proton and Neutron have about the same mass • Electron is about 2000 times less massive than proton • Electrical Forces produce attraction between electrons and the protons in the nucleus (they are oppositely charged) Physics 1100, Fall 2011

6. Chemical elements are defined by the number of protons in the atom’s nucleus • Hydrogen: 1 proton & 1 electron Cloud of “electron probability” proton 10-10 m Physics 1100, Fall 2011

7. Carbon has 6 protons Cloud of 6 electrons Nucleus: 6 protons 6 or 7 neutrons Physics 1100, Fall 2011

8. Atomic Number • We distinguish one element from another on the basis of the atomic number, which is the number of protons. • So, an atom of any element can have a variable number of electrons and neutrons, but given the number of protons, the fundamental properties of the element are unchanged. This is the basis for Dmitri Mendeleev’s organization of the Periodic Table of the Elements. The table is a way of organizing elements on physical grounds, but also serves to group elements with consistent chemical properties. Physics 1100, Fall 2011

9. The Periodic Table Elements in columns (groups) have similar outer-electron configurations, and so tend to behave similarly. alkali earths transition metals halogens alkalis rare earths noble gases Physics 1100, Fall 2011 actinides

10. The Periodic Table: the Bulk Earth A small number of elements make up >99% of the solid Earth. O = oxygen Na = sodium Mg = magnesium Al = aluminum Si = silicon S = sulfur Ca = calcium Fe = iron Ni = nickel Physics 1100, Fall 2011

11. Physics 1100, Fall 2011

12. Atomic Weight: It’s all in the Nucleus • Since electrons weigh virtually nothing, the mass of an atom is concentrated in its nucleus. • Each atom can be described by its atomic weight (or mass), which is the sum of the protons and neutrons. BUT... although each element has a defined number of protons, the number of neutrons is not fixed. Atoms with the same atomic number but variable numbers of neutrons are called isotopes. lithium: atomic number = 3 3 protons 4 neutrons atomic weight = 3 + 4 = 7 Physics 1100, Fall 2011

13. But that’s not all! • Antimatter • Each elementary particle has an “antimatter” counterpart Electron – Positron Proton – Antiproton Neutron – Antineutron etc. - anti-etc. • E=mc2 says matter and energy are interchangeable • If they find one another – major fireworks! • Dark Matter • Invisible, but must be there for gravitational attraction • Dark Energy • Invisible, but must be there for repulsion (universe expanding at an increasing rate! Physics 1100, Fall 2011

14. The Standard Model of Particle Physics Basic Ingredients are quarks and the electron-like objects (leptons) Fundamental forces are mediated by photon, gluons, W’s and Z’s (bosons) (Fermilab) Physics 1100, Fall 2011

15. Structure of the Atom Physics 1100, Fall 2011

16. What holds the nucleus together? • Electrical charges interact, and like charges repel • Opposites attract, of course • The closer they get, the more protons in the nucleus should be repelled from each other! • Something must serve as the glue to hold the nucleus together • The “strong” nuclear force: overcomes the electrical “Coulomb” force at short distances • Felt by protons and neutrons, not by electrons or their cousins (collectively called leptons) Physics 1100, Fall 2011

17. The Essence of Matter • Classification of matter? • • Elements, • • compound, • • mixture, ... • Three (actually 4) states of matter. • • Solid-fix shape, fix volume • • Liquid- shape container, fix volume • • Gas- shape container , volume container Physics 1100, Fall 2011

18. Class Problem • Oops! Those "harmless" germanium capsules you just swallowed may have an extra proton in each nucleus.Is this good news or bad news? Why? Physics 1100, Fall 2011

19. Class Problem • Suppose you could add or subtract protons from oxygen nuclei. To turn oxygen into gas that would glow red when an electric current flows through it, would you add or subtract protons? How many? Physics 1100, Fall 2011

20. Class Problem • Suppose you could add or subtract protons from oxygen nuclei. To turn oxygen into gas that would glow red when an electric current flows through it, would you add or subtract protons? How many? • Add two protons to each nucleus of oxygen and you increase the atomic number from 8 to 10. You then have neon, which will glow a very nice red when a current flows through it. Physics 1100, Fall 2011

21. Class Problems • 1. Which of the following statements is true? • A) There are thousands of different kinds of atoms that account for a wide variety of substances. • B) A large atom can be photographed with the aid of an ordinary microscope. • C) An atom is the smallest particle known to exist. • D) There are only about 100 different kinds of atoms that combine to form all substances. • E) None of these statements are true. • 2. What makes an element distinct? • A) the number of electrons • B) the number of protons • C) the number of neutrons • D) the total mass of all the particles • E) none of these Physics 1100, Fall 2011

22. Class Problems • 3. Which of the following is not a compound? • A) air • B) salt • C) ammonia • D) water • E) All are compounds. • 4. Solid matter is mostly empty space. The reason solids don't fall through one another is because • A) of electrical forces. • B) of nuclear forces. • C) atoms are constantly vibrating, even at absolute zero. • D) of gravitational forces. • E) none of these Physics 1100, Fall 2011

23. Class Problems • 5. If an astronaut landed on a planet made of antimatter, there would be an explosion and • A) the astronaut would annihilate. • B) an amount of planet matter equal to that of the astronaut would annihilate. • C) the astronaut and an equal amount of the planet would both annihilate. • D) the planet would annihilate. Physics 1100, Fall 2011