VIEW: Atomic Mass & Atom Structure

Atomic Mass & Atom Structure

Periodic table of elements. Image courtesy of Wikimedia. 

You can learn a lot of information from the periodic table of elements! For example, you can learn about the structure of the atoms that make up each element by looking at information such as the atomic number and atomic mass. In other words you can figure out the number of protons, neutrons and electrons from information provided about each element on the periodic table.

The mass of a single proton is equal to one, while the mass of a neutron is very close to 1 (the mass of an electron is negligible). Therefore, the number of protons and neutrons will tell you the atomic mass of an atom of each element on the periodic table. For example. take a look at the element carbon on the periodic table. It has an atomic number of 6. Remember what the atomic number tells you? It tells you the number of protons in 1 atom of that element; therefore, you know carbon has 6 protons. On average, carbon contains 6 neutrons in the atom's nucleus as well. The number of protons plus the number of neutrons gives you the atomic mass of the element. Check the atomic mass of C on the periodic table: you'll notice it is approximately 12. That makes sense since it has 6 protons and 6 neutrons! 

In lighter elements, the number of protons and neutrons is roughly equal. As you move to the heavier elements, the number of neutrons relative to protons increases, causing the mass to be increasingly more than double the atomic number.  

Protons and neutrons form the nucleus of an atom, and electrons swarm around the nucleus. This swarming isn't completely haphazard, though. Electrons inhabit various energy levels, or shells. Very simply, the electron configuration shown in the periodic table indicates how many electrons are found in each shell, from innermost (closest to the nucleus) to outermost. For example, the electron configuration for calcium is 2, 8, 8, 2. How can you figure this out the number of electrons in an atom from the information on the periodic table? Check out the atomic number! Calcium's atomic number is 20. Add up the number of electrons in each shell (2+8+8+2) and what do you get? 20!

The number of electrons in the outermost shell of an atom determines the physical characteristics of an element (for example, how easily it can react with or bond to another element). An element with a full outermost shell does not easily react with other elements; they are located in the far right column on the periodic table of elements (inert gases). Elements with only 1 electron in their outermost shell react easily; they are located in the far left column. 

Here is an example of how to use the periodic table of elements to find information about the number of protons, neutrons and electrons in an atom of a particular element.