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Chem Chapter 4
Terms in this set (42)
What is an atom?
The smallest particle of an element that retains its identity in a chemical reaction
Who was the first to suggest the existence of atoms?
Democritus (400's b.c)
What did Democritus explain about atoms?
They were indivisible and indestructible.
Who was the next man to elaborate on the atom?
John Dalton (1700's)
List the 4 ideas presented in Dalton's Atomic Theory:
1. All elements are composed of tiny indivisible particles called atoms.
2. Atoms in a given element are identical, but different other elements.
3. Atoms are neither created nor destroyed in a chemical reaction.
4. A given compound always has the same formation & types of atoms.
What is the range of the radii of an atom?
What instrument can be used to observe individual atoms?
Scanning Electron Microscope
Who discovered the electron?
What tool did Thomson use to discover the electron? Describe it.
Cathode Ray Tube- A beam of electrons flowing from the positive electrode to negative electrode.
Negative end of a cathode ray
Positive end of a cathode ray
Electrons flow from where to where?
From Cathode to Anode.
What did Thomson originally name electrons?
Describe Thomson's experiment in full.
He sealed low pressure gases within glass tubes fitted with metal electrodes (Cathode Ray Tube). The result was a glowing beam flowing from the cathode to the anode. He knew that like charges repel and opposite attract, so he hypothesized that the glowing beam was full of tiny, fast moving, negatively charged particles, To find the charge to mass ratio of electrons, he conducted the same experiment, but also put magnets on the tops and bottoms of the tube. He found the ratio to be constant, no matter the type of gas or metal. Therefore, he knew that electrons were components to all types of atoms.
Who determined the quantity of an electron's charge?
Describe Millikan's experiment.
He put two negatively charged drops of oil in-between two charged plates. Using his observations on how the plates effected a drop's fall and the charge to mass ratio of an electron, he determined that the charge of an electron was 1.60x1019 coulomb.
What is the mass of an electron?
What is a proton?
A positively charged subatomic particle
What is a neutron?
A neutrally charged subatomic particle
***What is the charge of an electron? Proton?
Both have a charge of 1.
What is the relative mass of a proton? Neutron?
Both have a relative mass of 1
Who discovered the proton?
How did Eugen Goldstein discover protons?
He observed that larger, positively charged objects were traveling from anode to cathode in the cathode ray tube.
Who discovered the neutron?
What do scientists believe make up protons and neutrons?
What model of an atom did JJ Thomson propose? Describe it.
Plum-Pudding Model- Electrons were stuck in positively charged material, like raisins in dough.
Who performed the Gold-Foil experiment? In what year?
Ernest Rutherford (1911)
What are alpha particles?
Helium Ions with 0 electrons (He +2)
Describe the Gold Foil experiment in full.
He aimed a beam of alpha particles at a piece of gold foil surrounded by a fluorescent screen. He expected the particles to be absorbed, since the accepted atom model at the the time was the Plum Pudding Model. However, none of the particles absorbed. Most alpha particles went clean through the foil, some went through deflected a bit, and some were drastically deflected.
Describe the Rutherford atomic model.
The atom is mostly empty space. There is a tiny central core composed of protons and neutrons, while electrons are distributed around the nucleus and occupy most of the volume. This is the modern belief and is also called the nuclear atom.
If an atom were the size of a football field, how large would the nucleus be?
The size of a marble
What makes one element different from another?
The number of protons.
What is the atomic number?
The number of protons in the nucleus of an atom. (H=1, Hg=79)
What is the mass number?
The number of protons and neutrons in the nucleus of an atom. (C-12 = 6p + 6n)
What is an isotope?
An atom that has a regular number of protons do but that has a different number of neutrons.
What is atomic mass? What is the formula?
A weighted-average mass of the atoms in a naturally occurring sample of an element.
What is an atomic mass unit?
1/12 the mass of a Carbon-12 atom. A single unit which describes the relative mass of a proton or neutron.
What is an ion?
Atoms that acquire an electrical charge due to the loss or gain of electrons.
What is the standard reference isotope?
Recommended textbook explanations
Chemistry: The Central Science
Bruce Edward Bursten, Catherine J. Murphy, H. Eugene Lemay, Matthew E. Stoltzfus, Patrick Woodward, Theodore Brown
Chemistry: Structure and Properties
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