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Transcript of Early Ideas About Matter - Home - Lancaster City School ... Theory... · word atom is derived....
Lesson 1-1
Democritus (460–370 BC) believed that matter is made of small, solid objects called atomos, from which the English word atom is derived.
Early Ideas About Matter
Lesson 1-1
Early Ideas About Matter (cont.)
• Aristotle (384–322 BC) did not believe that empty space exists, but instead believed that all matter is made of fire, water, air, and earth.
• Because Aristotle was so influential, his ideas were accepted and Democritus’s ideas about atoms were not studied again for more than 2,000 years.
Lesson 1-2
John Dalton combined data from his own scientific research with data from the research of other scientists to propose a new atomic theory.
Dalton’s Atomic Model
Lesson 1-3
An atom is the smallest piece of an element that still represents that element.
The Atom
What is a copper atom?
Lesson 1-3
• Atoms of different elements are different sizes, but all are very, very small.
• You cannot see atoms with just your eyes or even with most microscopes.
The Atom (cont.)
How would you describe the size of an atom?
Lesson 1-3
• The 1981 invention of a high-powered microscope, called a scanning tunneling microscope (STM), enabled scientists to see individual atoms for the first time.
• Scientists have learned that atoms are not the smallest particles of matter.
The Atom (cont.)
Lesson 1-4
Following his experiments with cathode ray tubes, scientist J.J. Thomson concluded that cathode rays were made of small, negatively charged particles which he called electrons.
Lesson 1-4
An electron is a particle with one negative charge (1–).
Thomson—Discovering Electrons
electron
from Greek electron, means ―amber,‖ the physical force so called because it first was generated by rubbing amber. Amber is a fossilized substance produced by trees.
Lesson 1-4
• Because atoms are neutral, or not electrically charged, Thomson proposed that atoms also must contain a positive charge that balances the negatively charged electrons.
• Thomson’s proposed atom was a sphere with a positive charge evenly spread throughout and negatively charged electrons within it.
Thomson—Discovering Electrons (cont.)
Lesson 1-4
Thomson’s model of the atom contained a sphere of positive charge with negatively charged electrons within it.
Lesson 1-5
Scientist Ernest Rutherford set up experiments to test Thomson’s atomic model and to learn more about what atoms contain.
Rutherford—Discovering
the Nucleus
Lesson 1-5
Rutherford expected the positive alpha particles to travel straight through the foil without changing direction.
Lesson 1-5
Some alpha particles traveled in a straight path, as expected. But some changed direction, and some bounced straight back.
Lesson 1-5
Rutherford—Discovering
the Nucleus (cont.)
Given the results of the gold foil experiment, how do you think an actual atom differs from Thomson’s model?
Lesson 1-5
• Rutherford concluded that most of an atom’s mass and positive charge is concentrated in a small area in the center of the atom called the nucleus.
• Additional research showed that the positive charge in the nucleus was made of positively charged particles called protons.
Rutherford—Discovering
the Nucleus (cont.)
Lesson 1-5
• A proton is an atomic particle that has one positive charge (1+).
• Negatively charged electrons move in the empty space surrounding the nucleus.
Rutherford—Discovering
the Nucleus (cont.)
Lesson 1-5
Rutherford’s model contains a small, dense, positive nucleus. Tiny, negatively charged electrons travel in empty space around the nucleus.
Lesson 1-6
• James Chadwick discovered that, in addition to protons, the nucleus also contained neutrons.
• A neutron is a neutral particle that exists in the nucleus of an atom.
Discovering Neutrons
Lesson 1-6
• Niels Bohr proposed that electrons move in circular orbits, or energy levels, around the nucleus.
• Electrons closer to the nucleus have less energy than electrons farther away from the nucleus.
Bohr’s Atomic Model
Lesson 1-6
• More research showed that, although electrons have specific amounts of energy, energy levels are not arranged in circular orbits.
• When an electron moves from a higher energy level to a lower energy level, energy is released—sometimes as visible light.
Bohr’s Atomic Model (cont.)
Lesson 1-6
In Bohr’s model of the atom, electrons move in circular orbits around the atom.
Lesson 1-6
Bohr’s Atomic Model (cont.)
How did Bohr’s model of the atom differ from Rutherford’s?
Lesson 1-6
• In the modern atomic model, electrons form an electron cloud.
• An electron cloud is an area around an atomic nucleus where an electron is most likely to be.
The Modern Atomic Model
Lesson 1-6
In this atom, electrons are more likely to be found closer to the nucleus than farther away.
Lesson 1-6
The Modern Atomic Model (cont.)
How has the model of the atom changed over time?
Lesson 1-6
• Protons and neutrons are made of smaller particles called quarks.
• Scientists theorize that there are six types of quarks: up, down, charm, strange, top, and bottom.
• Protons are made of two up quarks and one down quark.
Quarks
Lesson 1-6
• Neutrons are made of two down quarks and one up quark.
• The current atomic model might change with the invention of new technology that aids the discovery of new information.
Quarks (cont.)
Lesson 1 – LR1
A. atom
B. electron
C. nucleus
D. proton
Which term describes a particle with one negative charge?
Lesson 1 – LR2
Whose model of the atom contained a sphere of positive charge with negatively charged electrons within it?
A. Dalton
B. Democritus
C. Rutherford
D. Thomson
Lesson 1 – LR3
A. electron cloud
B. neutron
C. nucleus
D. proton
Which term refers to an area around an atomic nucleus where an electron is most likely to be?