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Democritus, Greek

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Proposed “atomos” as basic building blocks of matter. Changes in matter came from changes in arrangement of atoms

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Aristotle, Greek

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Disagreed with Democritus. He challenged a basic assumption that these atoms must move through nothingness. Believed in “hyle.” More influential philosopher.

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John Dalton , British

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Revived Democritus’ ideas because they were supported by modern observations including laws of conservation of mass, definite proportions and multiple proportions.

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Dalton's atomic theory?

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1. All matter is composed of extremely small particles (atoms). 2. Atoms of the same element are identical, and different than those of any other element. 3. Atoms cannot be created, divided, or destroyed. 4. Different atoms combine in small whole number ratios to form compounds. 5. In a chemical reaction, atoms are separated, combined, or rearranged.

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Cathode Rays

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Beam of particles traveling from cathode to anode.

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JJ thompson, British

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After studying cathode rays in the presence of different gases, both magnetic and electrical fields he concluded that the particles were part of all matter and negatively charged.

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Discorvery of the first subatomic particle?

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JJ Thompson

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Thompson calcuated a ______/______ ratio. He concluded that the particel was smalled than hydrogen, the smallest atom.

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charge/mass

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_____ ____ experiment establishes charge of particles

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oil drop

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Robert Millikan, American

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Millikan was able to counteract gravity by adjusting the charge on his two plates. Using Thomson’s ratio he also established the mass of the (electron).

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DAltons theory needed its first modification. which was

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Atoms could be divided into subatomic parts. The electron was part of every atom, had a negative charge, and a mass of about 1 /2000 th of hydrogen.

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Dalton's atomic Theory?

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1. All matter is composed of extremely small particles (atoms). 2. Atoms of the same element are identical, and different than those of any other element. 3. Atoms cannot be created, divided, or destroyed. 4. Different atoms combine in small whole number ratios to form compounds. 5. In a chemical reaction, atoms are separated, combined, or rearranged.

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In the absence of data to the contrary, JJ Thomson assumed that

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the light negative particles were spread throughout the atom like “plum pudding” or like a chocolate chip cookie

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Ernest Rutherford, New Zealand

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Gold Foil Experiment
Rutherford sent α particles through gold foil to determine what portion of the atom was positively charged. Very few particles were deflected from target.

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Blow up of gold foil – positive particles would be deflected by the positive part of the atom. Rutherford concluded that the positive part of the atom is a densely packed core (a small volume he called a nucleus). Nucleus accounts for most of the mass o

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[image]

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Henry Moseley British(1887-1915

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Confirmed Rutherford’s theory that the nucleus contained positively charged particles (protons.) Protons carry a charge equal but opposite to that of the electron.

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James Chadwick, British

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Discovered the neutron, also contained in the nucleus. A neutral particle, it carries no charge. The neutron has a mass approximately equal to a proton.

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Electron ....symbol? Location? charge? mass number? mass grams?

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e-
outisde nucleus
1-
1/1840
9.11 *10 (-28)

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proton ....symbol? Location? charge? mass number? mass grams?

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p+
inside nucleaus
1+
1
1.67 * 10 (-24)

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neutron ....symbol? Location? charge? mass number? mass grams?

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n
inside nucleus
0
1
1.67*10(-24)

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Henry Mosley working with Xrays discovered that each atom has a

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unique number of protons in the nucleus.

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Mosley arranged Mendeleev's periodic table according to the number of ___________________________________________________________________________

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protons he found in the nucleus

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Hydrogen ---->_________
1-------->_________
H-------->_________
1.008---->________

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element name
atomic number
symbol
average atomic mass

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# of protons= ___________

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atomic number

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protons also equeals # of

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electrons

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Isotopes

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atoms which have the same number of protons but different numbers of neutrons.

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Daltons Theory needed its second Modification.

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Daltons Atomic Theory – 1. All matter is composed of extremely small particles (atoms). 2. Atoms of the same element are identical, and different than those of any other element. 3. Atoms cannot be created, divided, or destroyed. 4. Different atoms combine in small whole number ratios to form compounds. 5. In a chemical reaction, atoms are separated, combined, or rearranged.

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The weighted average atomic mass depends on the

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isotopes of the element and their relative abundance.

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Radioactivity

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a process in which atoms spontaneously emit radiation (particles and energy) in order to achieve a more stable state.

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Radioactivity is peculiar to certain

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isotopes in which piling protons and neutrons together produce unstable nuclei.

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Radioactive decay

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– unstable nuclei losing energy by emitting radiation.

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Radioactive decay is a

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is a natural nuclear reaction.

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Nuclear reaction

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reactions which involve a change to the atom’s nucleus.

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In a nuclear reaction both the mass and

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charge of the nuclei must balance.

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The beta particle =

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an electron.

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Beta radiation has the effect of

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destroying a neutron to produce a proton and electron. The electron is emitted and the atomic number increases by 1.

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Gamma rays accompany

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α and β particles; account for most of the energy lost during decay.

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Gamma radiation has no

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mass or charge.

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alpha....symbol.?? mass?? charge??

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4
He
2
4
2+

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beta ,,,,,symbol.?? mass?? charge??

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0
B
-1
1/1840
1-

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gamma symbol.?? mass?? charge??

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0
v
0
0
0

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To balance a nuclear reaction

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both the mass numbers and the charge numbers must balance.

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Carbon Dating:

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Isotopes decay in a logarithmic pattern called a half-life.

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atom

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the smallest particle of an element that retains all the properties of that element; is electrically neutral , spherically shaped, and composed of electrons, protons and neutrons

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atomis mass unit

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(amu) one-twefth the mass of a carbon-12 atom

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electron

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a negativly charged fast moving particle with an extremly small mass that is found in all forms of amtter and moves through the empty space surrounding an atoms nucleus

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cathode ray

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a ray of radiation that originates from the cathode and travels to the anode of a cathode ray tube

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proton

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a subatomic particle in an atoms nucleus that has a positive charge of 1+

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nucleus

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the extremly small, positivly charged, dense center of an atom, that contains positivly charged protons, neutral neutrons it is surrounded by empty space through which one or more negativly charged electrons move

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atomic number

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the number of protons in an atom

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isotope

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atoms of the same element with the same number of protons but different number of neutrons

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mass number

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the number after an elements name, represently the sum of its protins and neutrons

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nuclear reaction

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a reaction that involves a change in the nucleus of an atom

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nuclear equation

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a type of equation that shows the atomic number and mass number of particles involved

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radition

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the rays and particles - alpha and beta particles and gamma rays that are emmitted by radioactive materials

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radioactivity

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the process in which some substances spontaneously emit radiation

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radioactive decay

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a spontaneous process in which unstable nuclei loose energy by emmitting radiation

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alpha particle

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a particle with two protons and two neutrons with a 2+ charge is equivilent to a helium -4 nucleus

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alpha radiation

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radiation that is made up of alpha particles ; is deflected toward a negativly charged plate when radiation from a radioactive source is directed bt 2 electrically charged plates

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beta particle

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a high speed electron with a 1- charge that is emitted during radioactive decay

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beta radiation

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radiation that is made up of beta particles; is deflected toward a positivly charged plate when radiation from a radioactive source is directed b/t 2 electrically charged plates

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gamma ray

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high energy radiation that has no electrical charge and no mass , is not deflected by electric or magnetic feilds usually accompanies alpha and beta radiation and accounts for most of the energy lost during radioactive decay

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nuclear equation

answer

a type of equation that shows the atomic number and mass number of particles involved

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nuclear reaction

answer

a reaction that involves a change in the nucleau of an atom

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