Outside nucleus in electron cloud 3 Parts of the Atom: Subatomic Particle Relative Mass Charge Where Found Proton 1 +1 In Nucleus Neutron 0(neutral) Electron -1 Outside nucleus in electron cloud

How many electrons can each energy level hold? 1st—2 2nd—8 3rd—18 4th –32

John Dalton: early 1800’s

Dalton’s 4 Points: All elements are composed of indivisible and indestructible atoms. Atoms of the same element are identical. Atoms of different elements are different. Compounds are formed from the joining of the atoms of 2 or more elements.

JJ Thomson--1897 Plum Pudding Model But the atom is Neutral!!!! While studying electric discharge in Cathode-ray tubes, Thomson discovered the electron!!!

What Rutherford Expected Ernest Rutherford--1908 Rutherford’s Gold Foil Experiment In an attempt to build on Thomson’s model, I discovered some amazing stuff!!! What Rutherford Expected Actual Results Rutherford’s Model

Rutherford’s Atomic Model Notice 2 things: Atom is made up of mostly empty space. Electrons are scattered randomly! Rutherford’s Atomic Model Rutherford discovered the nucleus!!

Nucleus Electrons Neils Bohr--1913

Bohr “Planetary” Model of the Atom The Bohr Model has the following features: There is a nucleus(Rutherford’s Discovery) The electrons move about the nucleus in “stationary, stable states”(later referred to as orbits)!

The Wave Model of the Atom

Atomic Number Chemical Symbol Element Name Average Atomic Mass

Atomic # Mass # # of protons in an atom In a neutral Atom, # of protons=# of electrons Atomic # of a given element will never change, therefore, the # of protons of an element will not change. Mass # Sum of the protons and neutrons Closest whole # to the Avg. Atomic Mass(from periodic table)

Average Atomic Mass Mass of atom in Atomic Mass Units Given on periodic table as average mass of all isotopes of that element.(we’ll discuss isotopes) Atomic Mass Unit—defined as 1/12 the mass of a Carbon-12 atom

Isotopes Atoms of the same element with the same # of protons, but different # of neutrons.

2 ways of writing Isotopes H-1 H-2 H-3 Each of these represents Hydrogen The number represents the mass # Each of these represents Carbon The top # represents the mass # The bottom # represents the Atomic #

Ions + ions 2. - ions Atoms become (+) by losing electrons A “charged” atom. Atoms become charged by gaining or losing electrons. 2 Types of Ions: + ions Atoms become (+) by losing electrons 2. - ions Atoms become (-) by gaining electrons

# p = 11 # e = 11 # n = 12 A # = 11 M # = 23 Atomic # Atomic Mass M # = # p + # n 23 = 11 + #n A # = 11 M # = 23

# p = 19 # e = 19 # n = 20 A # = 19 M # = 39 Atomic # Atomic Mass M # = # p + # n 39 = 19 + #n A # = 19 M # = 39

This is the model of the atom as we know it today!!!! Does anything strike you as odd? Knowing what you have learned at this point, is this what you would expect? Think in terms of electricity!! Does that change your thoughts any???

Forces within the Atom

1. ELECTROMAGNETIC FORCES Holds electrons in orbit around nucleus!! Electrons are kept in the orbit around the nucleus by the electromagnetic force, because the nucleus in the center of the atom is positively charged and attracts the negatively charged electrons.

If all the protons inside the nucleus are the same charge and repel, what keeps them from bursting and exploding the atom? ? ? How do they stay together? ? ?

2. Strong Force The strong forces oppose the electromagnetic force of repulsion between protons. Like ”glue” the strong force keeps the protons together to form the nucleus. The strong forces and electromagnetic forces both hold the atom together.

3. Weak Force Weak forces are important because they are responsible for stabilizing particles through the process of radioactive decay, in which a neutron in the nucleus changes into a proton and an electron.

4. Gravity mentioned last, is it the “weakest”! Inside the tiny nucleus of an atom, the effect of gravity is small compared to the effects of the other three forces.

Which force within the atom keeps the electrons in orbit around the nucleus? Strong Force Weak Force Electromagnetic Force Gravity

Which force within the atom keeps protons glued inside the nucleus? Strong Force Weak Force Electromagnetic Force Gravity

Which force within the atom is responsible for radioactive decay? Strong Force Weak Force Electromagnetic Force Gravity

1. Alpha decay 2. Beta Decay 3. Gamma Decay

In alpha decay, one radioactive nucleus is converted to another with atomic # decreased by 2 and Mass # decreased by 4 An Alpha particle is a Helium nucleus!!

In Beta decay, one radioactive nucleus is converted to another with the atomic # increased by one and the mass # left unchanged! In basic beta decay, a neutron is turned into a proton and an electron. The electron is then emitted. A beta particle is an electron!!

Gamma Decay Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma particle. A gamma particle is a high energy photon(electromagnetic radiation)

Penetrating Power

Which particle has the most penetrating power? Alpha particle Beta particle Gamma particle Zeta particle

Which particle has the least penetrating power? Alpha particle Beta particle Gamma particle Zeta particle

Nuclear Fission vs. Nuclear Fusion Nuclear Fission—big to small Nuclear Fusion—small to big Both release large amounts of energy!!

Nuclear Fission Nuclear fission involves the splitting of one nucleus into 2 smaller nuclei.

Nuclear Fission at work!!!!

Nuclear Fusion Nuclear Fusion involves the joining of 2 smaller nuclei into one larger nucleus

Nuclear Fusion

Discuss Nuclear Waste If you love your Children, Don’t take them to Yucca Mountain on vacation!!

Copy Summary Statements: p. 540, p. 545, p. 550 and p. 556