The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid,...

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The Atom Pg. 29

Transcript of The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid,...

Page 1: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

The Atom

Pg. 29

Page 2: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Early Theories

• There was no experimentation• Democritus- atoms are solid,

homogeneous, indestructible, and indivisible

• Aristotle- believed everything was made of either fire, water, earth, or air.

• John Dalton- all matter composed of atoms; all atoms of one element are identical; atoms can’t be created or destroyed (actually used experiments)

Page 3: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Evolution of the Atomic Theory• The electron- discovered by JJ Thomson using

a cathode ray tube; Robert Millikan discovered the negative charge

• JJ Thomson came up with the plum pudding model. An atom was a mass ( pudding) with electrons scattered throughout (plums)

• Ernest Rutherford discovered the nucleus using the gold foil experiment; said atom is mostly empty space with dense positive nucleus in the middle

Page 4: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.
Page 5: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Evolution of the atomic theory

• Rutherford did more experiments and concluded the proton was in the nucleus

• James Chadwick- discovered a neutral particle in the nucleus called the neutron

• Atom- smallest particle of an element that still retains that elements properties

Page 6: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

BEHOLD! An atom is born• Atom is spherical with a lot of empty space

where electrons (with little mass) exist. • In the middle, there is a small dense

nucleus (contains most the mass)that contains positively charged protons and neutral neutrons

Page 7: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Atomic Number

• The periodic table can be used to find the number of protons, electrons, and neutrons.

• The atomic number of an element (labeled Z) tells you how many protons there are.

• On the periodic table, the elements are listed as neutral elements so the number of electrons=the number of protons.

Page 8: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Z

Page 9: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Calculating # of neutrons

• The mass number (labeled A) is the number of neutrons + protons.

• Mass number=atomic mass rounded to the nearest whole number

• The atomic mass is located under the element symbol.

• You can find the number of neutron by subtracting the Atomic number (Z) from the Mass number (A)

• A-Z = # of neutrons

Page 10: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

Shorthand notation

• There is a way to represent atomic mass and number

• Steps:– 1-start with the element symbol– 2- place the mass number on the top left side of

the symbol– 3-place the atomic number on the bottom left side of

the symbol

Page 11: The Atom Pg. 29. Early Theories There was no experimentation Democritus- atoms are solid, homogeneous, indestructible, and indivisible Aristotle- believed.

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