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All About Atoms
Transcript of All About Atoms
Dalton’s atomic model just proposed that all substances were made of atoms.
He included five points in his model, which condensed, equal to:
All substances are made of atoms
Atoms cannot be destroyed, divided, or created
Atoms can combine to form compounds
Chemical reactions are made because of atoms being rearranged, separated, or combined.
He did not include any information on electrons or nuclei.
Thompson's atomic model
Thompson’s atomic model expanded upon Dalton’s model due to the discovery of electrons; the nucleus had not been discovered yet.
This model is often called the “Plum Pudding model” because of the way the negative electrons and positive protons “floated” around in the atom similarly to the way plums and raisins “floated” around a fruitcake.
The part of the atom that these floated around in was referred to as the “soup.”
Rutherford's atomic model
Rutherford’s atomic model was developed after the Thompson’s “Plum Pudding model.” He introduced the idea of the nucleus, which was the idea of the atom having a central charge.
However, he did not use the word “nucleus” at the time. Electrons orbit around the nucleus, forming the electron cloud.
Electrons are the negatively charged particles in an atom. They are the subatomic particle with the least amount of mass.
Electrons also determine the chemical properties of the atom they belong to.
The electrons are located in the electron cloud, which is the outer area of the atom.
The electrons are attracted to the protons inside of the nucleus due to electromagnetic force.
Protons are the positively charged particles in an atom’s nucleus. The nucleus is composed of the atom’s protons and neutrons.
Protons are very important; the number of protons determines what element the atom is.
No matter what changes in an atom, as long as the number of protons stays the same, it is still an atom of that element.
The number of protons in an atom is its atomic number; more on that later.
Neutrons are the neutral particles in the nucleus. They do not have a charge.
The number of neutrons inside of an atom determines the isotope of the atom’s element. Neutrons also help to provide a barrier between the many protons in the nucleus.
The atomic number is simply the number that tells you what element an atom is. The number of protons is what the atomic number is; this is visible on the periodic table.
For example, silver has 47 protons; its atomic number on the periodic table is 47.
The atomic mass is the mass of an atomic model, obviously. You can find the atomic mass by finding out the atomic number (the number of protons) and the number of neutrons in an element.
For this example, let’s use silver. Silver’s atomic number is 47, and it usually has 61 neutrons. Add the two together and you get 108; this is the atomic mass.
Isotopes are just atoms of the same element that have the same number of protons and electrons, but the number of neutrons in the atom differs.
This relates to the average atomic mass, which will be explained later.
Isotopes have different atomic mass and some isotopes are more stable than others. Unstable isotopes break down through radioactive decay.
Average Atomic Mass
The average atomic mass is simply the atomic mass calculated using the isotopes of the element.
For example, you would take the two stable isotopes of silver and add together the protons and the neutrons separately for those two.
You would then add the two totals together and divide by 2 to get the average atomic mass.
How to find the average atomic mass
Using silver as an example again, two stable isotopes are 47 protons and 60 neutrons and 47 protons and 62 neutrons.
This means that the totals are 107 and 109; you would refer to these as silver 107 and silver 109.
The average of 107 and 109 is determined by multiplying silver 107 and silver 109's total by the percentage that they make up of silver.
Once you get that, you divide by 100, and you have your answer!
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"Models of the atom." Everything Science. N.p., n.d. Web. 26 Aug. 2013. <http://everythingscience.co.za/grade-10/04-the-atom/04-the-atom-02.cnxmlplus>.
"Rutherford model." Wikipedia. N.p., n.d. Web. 26 Aug. 2013. <http://en.wikipedia.org/wiki/Rutherford_model>.