Today we learned about the numbers used to describe certain atoms and elements. We once again chanted the phrase "atomic number, number of protons" to make sure everyone understood it, and then we dealt with how to find different quantities within atoms (such as number of protons, number of neutrons, number of electrons, and so on). The atomic mass can be expressed in two ways: as a whole number, which is found by adding the protons and neutrons, and by the decimal listed on the periodic table, which is the element's exact mass in amu units. If you subtract the number of protons from the exact atomic mass, you can determine the number of neutrons in the nucleus, and if this number is a decimal, round it to the nearest whole number. Then you have an isotope! The exact mass on the table is the mass of the element's most common isotope. Protons, neutrons, and electrons will not always be the same as one another, but in a neutrally-charged atom (where neither positive nor negative charges dominate) they are.
Problems for Lesson 12:
2.) What does the atomic mass tell you? The number listed alongside an element in the table is the atomic mass, and it tells you the average mass of the protons and neutrons within the nucleus of an element of that atom. Usually that number is listed as a decimal, which represents the average mass of the most commonly observed isotope of an atom.
4.) If you wanted to identify an element, what one piece of information would you ask for? The only piece of information you would need to identify an element is the atomic number. This identifies the number of protons, and if you change the protons, that means you change the element!
5.) Why does an atom of carbon (C) have a larger atomic mass than an atom of boron (B) if they have the same number (6) of neutrons? Boron and carbon do not have the same atomic number. With one having more or less protons than the other, it doesn't matter if they have the same number of neutrons. Protons carry more mass in the nucleus.
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