Atoms: The Building Blocks of Matter Chapter 4 Ancient Atomic Theory Ancient Atomic Theory Modern Atomic Theory P.24 Warm up: Has our view of atoms changed over time? Give an example.

Dalton’s Atomic Theory (1808) Dalton’s Atomic Theory (1808)  Atoms cannot be subdivided, created, or destroyed  Atoms combine in simple whole-number ratios to form compounds  In chemical reactions, atoms are combined, separated, or rearranged  All matter is composed of atoms  Atoms of an element are the same; atoms of different elements differ. John Dalton

Dalton’s Acrostic p23 D A L T O N Use your whole left page to write an acrostic explaining Dalton’s atomic theory. Use the letters of his name to come up with a word to describe his theory.

Discovery of the Electron p26 Warm up: What do opposite charged particles do? Similar charged particles? In 1897, JJ Thomson used a cathode ray tube to detect the electron Particles attracted to positive plate, so are negatively charged.

Thomson’s experiment p25 Draw the picture of Thomson’s experiment: Write a letter to someone special explaining how Thomson used a cathode ray tube to discover the electron and its charge.

Some Modern Cathode Ray Tubes

Thomson’s Atomic Model p26 Thomson believed that the electrons randomly scattered in a positively charged “pudding,” the “plum pudding” model.plum pudding

Mass of the Electron Electron 1909 – Robert Millikan determines the mass of the electron. The oil drop apparatus Mass of the electron is 9.109x kg

Plum Pudding Model of Atom p25 Draw a picture representing Thomson’s plum pudding model. Label the electrons and the charges within the atom. Explain why he called it “plum pudding”

Rutherford’s Gold Foil ExperimentRutherford’s Gold Foil Experiment p28 Rutherford’s Gold Foil Experiment  Alpha particles are pos charged  Particles fired at gold foil  Particle hits the detecting screen & are recorded Warm Up: what particles are in the nucleus? What are their charges?

Rutherford’s Findings p28  The nucleus is small and densenucleus  The nucleus is positively charged  The nucleus is in the center with electrons surrounding it  Most of the particles passed right through  A few particles were deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions:

Rutherford’s experiment p 27 Draw the gold foil experiment: How did Rutherford discover a nucleus in the atom? How did he figure out the charge?

Rutherford’s Atomic model p 27 Draw a representation of Rutherford’s model of the atom. Label where the protons and electrons are and their charges.

Modern Atomic Theory p30 Warm up: draw chart and fill in blanks ParticleChargeMass (kg)Location Electron x AMU Proton x AMU Neutron x AMU AMU = Atomic Mass Unit

Mass Number p30 Mass # = protons + neutrons always a whole number NOT on the Periodic Table! 12 6 C © Addison-Wesley Publishing Company, Inc.

Atomic Number Atomic Number p.30 Atomic Number The number of protons in the nucleus. Unique for every element. (found on periodic table) 12 6 C Element# of protons Atomic # (Z) Carbon66 Phosphorus15 Gold79

IONSIONS p30 IONS In neutral atoms, electrons equal the atomic number. Ions are atoms that have gained or lost electrons. They will have a + or – charge Ex) Cl - has 1 extra electron, Cl + has lost 1 electron. Cl -2 has gained 2 electrons, etc.

Practice Practice Elementp+p+ n0n0 e-e- Mass # 18 O 10 As P

Atomic Structure Quiz 39 Ca How many Protons:________ Neutrons:________ Electrons:________

Isotopes atoms of the same element that differ in the number of neutrons Elements occur in nature as mixtures of isotopes. isotopes Isotopes & Atomic Mass p32 Warm up: explain how you find an average

IsotopeSymbolComposition% in nature Carbon C6 protons 6 neutrons 98.89% Carbon C6 protons 7 neutrons 1.11% Carbon C6 protons 8 neutrons <0.01% Atomic mass p32 of an element is the average of all the naturally occurring isotopes and its abundance. Found on the periodic table Ex. Carbon =

Average Atomic Mass Calculation p32 EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O amu

Subatomic Particles Most of the atom’s mass. QUARKS equal in a neutral atom but not in an ION Equal to atomic #

The Quark… Oops…wrong Quark!