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Ch. 4 test

Development of the Atomic Theory

The word Atom comes from what Greek word? And what does it mean? Atoms and it means "Not Able to be divided"
Which is part of Democritus's theory about atoms? A. Atoms are small, soft particles. B. Atoms are always standing still. C. Atoms are made of a single material D. Atoms are small particles that can be cut in half again and again. C Atoms are made of a single material.
Why did people ignore Democritus's ideas for such a long time? Aristotle was more popular than Democritus's so Aristotle was believed more than Democritus. Democritus was right and Aristotle was wrong.
The smallest unit of an element that maintains the properties of that element is a(n)_______ Atom
What was not one of Dalton's theories? A. All substances are made of atoms B. Atoms of the same element are exactly alike. C. Atoms of different elements are alike. D. Atoms join with other atoms to make new substance. C. Atoms of different elements are alike.
Dalton experimented with different substances. What did his results suggest? That elements combine in certain proportions because the are made of single atoms.
In Thompson's experiments with a cathode-ray tube he discovered that a(n)_____ charged plate attracted the beam. He concluded that the beam was made up of particles that have ______ charge. Positively Negative
The negatively charge subatomic particles that Thompson discovered are now called______ Electrons
Before his experiment what did Rutherford expect the particles to do? He expected the particles to pass right through the gold foil.
What were the surprising results of Rutherford's gold-foil experiment? Some of the particles were deflected.
In 1911, Rutherford revised the atomic theory. What was not part of that theory? The nucleus is made up of protons and electrons.
The center of an atom is a dense region consisting of protons and neutrons called the_____. Nucleus
What are electron clouds? There are regions inside the atom where electrons are likely to be found.
Protons are Negative or Positive? Positive P+
Where are the protons located? Inside the nucleus.
Neutrons are ____ charged neutrally charged particles N*
Neutrons are located _______. Inside the nucleus.
Neutrons job is to what? Keep the positively charged protons from repelling each other (act like strong glue)
Electrons are _______ charged Negatively charged E-
Electrons are located _____. Outside the nucleus in the electron cloud.
Electrons are extremely______. TINY!!!!
Today there are______ known elements. 118
The atomic number is.... The number of protons in the nucleus.
What is the Atomic Mass Unit? A unit of mass that describes the mass of an atom or molecule
What is the Atomic Number? The number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element.
What is an isotope? An atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a a different number of neurons (and thus a different atomic mass)
Mass Number? The sum of the numbers of protons and neutrons in the nucleus of an atom.
The atomic mass The mass of an atom expressed in atomic mass units.
how do you find the number of neutrons? mass number - number of protons (atomic Number) _______________________ number of neutrons
Created by: sophiacuttill