All About Atoms (7th)

Our first unit this year is Chemistry and we start by reviewing what they learned in 5th grade. So, we review the parts of an atom! We then add a little more to it and learn all about atomic models and the atoms of different elements.

In our notebooks, we created a timeline (to scale) for developments of different atomic models. They do have to know the different scientists we discussed and the contributions of each. The timeline includes a foldable we filled out to help them remember the different scientists.

We then reviewed the location and charges for protons, neutrons, and electrons. We filled out another foldable. I found the idea on another teacher's site and then used Publisher to make one for us! We went through everything together and they filled it out. We'll get it glued into our notebooks, but they need it for homework right now.

For their homework, they need to know how to calculate the mass number, atomic number, and the number of protons, neutrons, and electrons. Here are the instructions we went over in class:

• Mass number = # protons + # neutrons
• Atomic number = # protons (they are always the same number!)
• Protons = atomic number (see above) OR Protons = mass number - # neutrons 
• Neutrons = mass number - # protons
• Electrons = # protons OR atomic number

For example: Iodine has a mass number of 127 and an atomic number of 53. So, Iodine has 53 protons (atomic number), 53 electrons (# protons), and 74 neutrons (127 - 53).

We also started learning how to draw Bohr diagrams and Lewis dot structures. A Bohr diagram shows all the electrons that an atom has; whereas, a Lewis dot shows only the valence, or outermost, electrons. In a Bohr diagram the energy levels are shown as rings around the center and the electrons are added to each ring until the energy level is full. This is the Bohr model for an element with 11 protons and 11 electrons. Notice that the first energy level has the only 2 electrons it can hold spaced as far apart as possible because like charges repel. The second energy level will have the electrons spread as far as possible for the first 4, then the electrons start pairing up (this has to do with orbitals-the s, p, and ds that are outside of what we cover in 7th grade). The electrons continue filling the 2nd level until it contains all 8 it can hold, then start filling the 3rd level. We won't have more than 3 energy levels for this class. Also, we have not yet started discussing the periodic table, so students do not need to try to figure out which element this would be.



The Lewis dot structure would be easier to draw because it only shows the valence electrons. These are the outermost electrons an atom has. It is important to be able to tell how many valence electrons an atom has because these are the electrons that are involved in chemical bonds and atoms will react in certain ways with other atoms based on the number of valence electrons. For now, students will determine the number of valence electrons an atom has by looking at the Bohr diagram (we will learn how to do that using the periodic table, but that comes later). For the atom above, it would look like this: