2. Atoms and the Periodic Table
John Dalton, one of the "Fathers of Chemistry"is credited with modernizing the Atomic Theory.
The Modern Atomic Theory
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in our exploration to understand the atom. We now look at the atomic theory now. It was democratization around 400 BC who first discussed the Adam itself and John Dalton, 18 03 Try to take a more modernized view of the atom. Now Adam comes from the Greek word Ademas, which means undivided. Yes, and Dalton was able to take portions of democracies view of the atom as well as lovers source. Conservation of Mass to help formulate his atomic theory. Now here we're going to compare and contrast. Dalton's atomic theory postulates. Basically, the five principles that he held in terms of the atom versus arm or modern atomic view now realize that Dalton in his time didn't have electron microscopes and some of the technology that we have here. So it's still pretty astonishing that he was able to come with some of these concepts with the atom. The first postulate Dalton had was that all matter is composed of atoms, and they're the smallest particles of matter. We, on the other hand, in modern atomic theory, we agree that matter is composed of atoms, but we could go even further into the atom and look at atoms. Three subatomic particles, the protons, neutrons and electrons. Of course, Dalton didn't have microscopes powerful enough to look inside of the atoms, so it's totally understandable that he didn't know about the presence of these three subatomic particles. Now his second postured, he said that atoms are indivisible and therefore cannot be created or destroyed. This kind of sounds like lava source. Conservation of matter or max matter cannot be created nor destroyed. All that happens is it changes forms Modern chemist agree with this second postulate. Dalton's third postulate is that all atoms of a given element are identical in mass sides and properties. So, for example, all carbon atoms, according to John Dalton, were exactly the same. Modern chemists don't necessarily agree with that. They say that not all atoms of a given element are identical and exist in the same form. Why? Because we know the presence of isotopes. Remember, there's carbon 12, and then there's carbon 13. So here they have the same atomic number. Yes, born, you subtract the mass number by the atomic number, you get the number of neutrons, so Carbon 12 has six neutrons, but Carbon 13 has seven neutrons so they're gonna have differences in Mass. Their mass numbers are not the same, so the same atoms can have different masses and densities. We see that with the examples of our isotopes. They have same number of protons, but different mass numbers. So they're masses are the same. The same atoms can connect in different ways to give rise to different compounds. For example, the most common form of carbon is graphite. Now, in pencils, we no longer use lead in pencils. We use graphite because it's not toxic. But this isn't the only form of carbon that exist. There's also carbon diamond, which is the more valuable form of carbon, as well as other types of carbon that we've created within labs. All of them are carbon, but they come in different forms. Dalton never accounted for these phenomenon. Now different atoms can have identical masses. So, for example, are gone 40 and crossing 40. They both have ah mass number of 40 but they're not the same element now. Postulate four postulate four. John Dalton said that compounds are made up of two or more different types of atoms in fixed, simple whole number ratios. For example, water was composed of two hydrogen, one oxygen carbon dioxide, one carbon to oxygen's ammonia, one nitrogen, three hydrogen. But modern chemists say Adams don't always combined in fixed, simple whole number ratios. They can be complex, so a good example of this is blue co sugar. So it's much more complex than Dalton first postulated, has six carbons 12 hydrogen, six oxygen's Then, finally, Dalton believed that a chemical reaction is a rearrangement of atoms. Why? Because a matter cannot be created or destroyed, it just changes forms. Modern chemists agree with this idea. Matter cannot be created nor destroyed. It's just a rearrangement of those atoms within chemical reactions. So we can see that although some of Dalton's postulates were proven to be not entirely true or wrong, we can see that a great deal of them helped to establish the basis for modern atomic theory. So now that we've seen the contributions by John Dalton and the more modernized modern atomic theory, let's take a look at some practice questions and example questions
Atomic Theory Example 1
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here in this example question, it says which of the following statements are consistent with Dalton's atomic theory, as it was originally stated. So here we're following just Dalton's first five original postulates. We're not taking a look at the modern atomic theory, which chemist today used through the use of further experimentations and instrumentation. So here, for one, nitrogen and phosphorus atoms have the same mass. Remember, Dalton wasn't aware of isotopes. He wasn't aware that different elements could have the same mass number and therefore atomic Mass, So this would not be consistent when his original posturings next all let Adams are identical. This is almost word for word, one of his postulates, he said, that identical elements or identical Adams should possess the same mass size and properties, so this would be consistent to barium and chlorine atoms, combined in a 1 to 2 ratio to form barium chloride. So barren chloride is B a C. L two. There is one barium to two Korans. This is consistent with Dalton's original postulate, or Adams combined in simple whole number ratios. Then, finally, uranium atoms undergo Alfa decayed to become thorium Adams. This is really talking about radioactive processes which do occur. But again, in Dalton's time, he didn't know that this could happen. So this does not go with one of his five original postulates. So out of the choices on Lee Option two and three could be consistent with Dalton's original atomic theory, so that would give us options see as a correct answer.
Which of the following is NOT a component of Dalton's Atomic Theory?
A chemical reaction rearranges the grouping of atoms.
Atoms are composed of protons, neutrons, and electrons.
Atoms of a given element are chemical and physically identical.
Atoms of different elements combine in simple, whole number ratios to form compounds.
Matter is composed of atoms that are unable to divided any further.
Dalton used the lightest element as his standard for atomic mass. What is this element?