Chapter 4 Atoms

1. Chapter 4Atoms

2. The Development of Atomic Theory • Greek philosopher Democritus suggested that the universe was made of invisible units • He called these units: atoms from the Greek word (atomos) that means “unable to be cut or divided”

5. The Development of Atomic Theory • Dalton’s Atomic Theory • 1808 • Atoms cannot be divided • All atoms of a given element were exactly alike, and atoms of different elements could join to form compounds • Law of definite proportions • A chemical compound always contains the same elements in exactly the same proportions by weight or mass

10. The Development of Atomic Theory • Thomson’s Model of the Atom • 1897 • Cathode-ray tube experiment suggested that cathode rays were made of negatively charged particles that came from inside atoms • This result revealed that atoms could be divided into smaller parts • Discovered electrons, negatively charged particles inside the atom

13. The Development of Atomic Theory • Thomson’s Model of the Atom • Plum-pudding model • Electrons are spread throughout the atom, just as blueberries are spread throughout a muffin

15. The Development of Atomic Theory • Rutherford’s Model of the Atom • Proposed that most of the mass of the atom was concentrated at the atom’s center • Gold-Foil Experiment • Suggested that an atom’s positive charge is concentrated in the center of the atom called the nucleus • Data suggested that compared with the atom, the nucleus was very small

18. The Development of Atomic Theory • Rutherford’s Model of the Atom • New model: negative electrons orbit the positively charged nucleus in much the same way that planets orbit the sun

25. The Structure of Atoms • ATOM • *IS THE FUNDAMENTAL UNIT OF MATTER • *COMPOSED OF SUBATOMIC PARTICLES • *ATOMIC NUCLEUS • *PROTON • *NEUTRON • *ORBIT (OUTSIDE) THE NUCLEUS • *ELECTRON

30. The Structure of Atoms • LOCATION MASS CHARGE • ( in amu) • ____________________________________________ • PROTON nucleus 1 +1 • ____________________________________________ • NEUTRON nucleus 1 0 • ____________________________________________ • ELECTRON outside 1/2000 -1 nucleus • ____________________________________________

31. The Structure of Atoms • The electric force holds the atom together • Positive and negative charges attract each other with a force known as the electric force • Protons and electrons are attracted to one another by the electric force

36. The Structure of Atoms • ATOMIC NUMBER — THE NUMBER OF PROTONS IN THE NUCLEUS OF THE ATOM. • *BEFORE AN ATOM REACTS THE NUMBER OF PROTONS AND ELECTRONS ARE EQUAL

41. The Structure of Atoms • MASS NUMBER (ATOMIC MASS) — IS THE • SUM OF THE PROTONS AND NEUTRONS IN THE NUCLEUS OF THE ATOM. • *amu = 0.000,000,000,000,000,000,000,001,67 g • Equal to 1/12 of the mass of a carbon-12 atom • *Electron mass is so small (negligible) that when calculating MASS NUMBER of an atom the mass of the electron is considered zero ( 0).

44. The Structure of Atoms • ISOTOPES — ATOMS OF THE SAME ELEMENT THAT HAVE THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS.

48. The Structure of Atoms • The mole is useful for counting small particles • Since chemist deal with large numbers of small particles, they use a large counting unit called the mole (mol) • 1 mol=602,213,670,000,000,000,000,000 particles • 6.022 x 1023 • Called Avogadro’s number

49. The Structure of Atoms • Mole: the SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in exactly 12 g of carbon-12 (This is a single isotope) • But, the average atomic mass of carbon is 12.01u when considering the other isotopes