Having demonstrated how to draw a few simple atoms, I had students fill out a periodic table template with drawings of the first twenty atoms. Actually, I only had them draw the electrons in their shells because it reduced the messiness of trying to fit in forty nuclear particles into a small tile, and the point I wanted to get at was the pattern of shells and valence electrons in the periodic table.
The end result looked something like this:
Students learn the relationship between electron configuration and position in the periodic table. Diagram by E.F..
All the drawing only took about 15 minutes, and once they’d figured out the first half dozen or so it started to get a little boring. But that freed up the cognitive resources so they could notice the two key patterns.
First, each row in the periodic table has an additional electron shell.
Second, as you go across a row you add one electron to the shell until it is filled.
It’s a first glimpse at the periodicity in the periodic table. And it sets us up nicely to be able to talk about chemical bonding.
Before: Barren, Volcanic. Image by Ben Tullis via Wikimedia Commons.
Charles Darwin and colleagues attempted to vegetate the barren, volcanic Ascension Island with plants from botanical gardens around the world. Essentially, it was an experiment in transforming. And it worked. Howard Falcon-Lang has the details at the BBC.
After: An eclectic, lush mix of vegetation. Image by LordHarris via Wikimedia Commons.
This year, I’ve been basing my introduction to basic chemistry for my middle school students around the periodic table of the elements. The first step, however, is to teach them how to draw basic models of atoms.
Prep: Memorization over the Winter Break
I started it off by having the students memorize the first 20 elements (H through Ca), in their correct order — by atomic number — over their winter break.
A diagram of an oxygen atom.
So that they’d have a bit of context, I went over the basic parts of an atom (protons, neutrons, and electrons) and made it clear that the name of the element is determined solely by the number of protons. I even had them draw a few atoms with the protons and neutrons in the center and the electrons in shells. Since I’d dumped all of this on them in a single class period, it probably was a bit much, but since it was just to give them some context I did not expect the 7th graders, who had not seen this before, to remember it all; for the 8th graders it should have been just a review.
Most students did a good job at the memorization. Some found songs on the the internet that helped, while others just pushed through. Having the two weeks of winter break to work on it probably helped too.
Day 1. Lesson: The Parts of an Atom
When we got back to school, the first thing I did was give them an outline of the upper part of the periodic table and asked them to fill it in with the element names.
Template for the first 20 elements of the periodic table. (pdf)
After they’d filled out their periodic table template, I went into the parts of the atoms in more detail, and had them practice. The key points I wanted them to remember were:
The atomic number is written as a subscript to the left of the element symbol.
The atomic number is the number of protons. Since they memorized the elements in order, they should be able to figure this out on their own — but they could also look it up quickly on the periodic table, or look at the element symbol where the atomic number is sometimes written on the lower left.
The atoms have the same number of electrons as protons. Protons are positively charged, and electrons are negatively charged, so an atom needs to have the same number of both for its charge to be balanced. We don’t talk about ions –where there are more or less electrons– until later.
The atomic mass (4) is written as a superscript to the left of the element symbol. The atomic mass is the sum of the number of protons (2) and the number of neutrons (2).
The small atoms that we’re looking at tend to have the same number of neutrons as protons, but that’s not necessarily the case. So how do you know how many neutrons? You have to ask, or look at the atomic mass number, which is usually written to the upper left of the atom. Since the atomic mass is the sum of the number of protons and neutrons, if you know the atomic mass and the number of protons, you can easily figure out the number of neutrons. (Note that electrons don’t contribute to the mass of the atom because their masses are so much smaller than the masses of neutrons and protons.
This oxygen atom has 8 electrons in two shells.
Electron Shells: Electrons orbit around the nucleus in a series of shells. Each shell can hold a certain maximum number of electrons (2 for the first shell; 8 for the second shell; and 8 for the third). And to draw the atoms you fill up the inner shells first then move on to the outer shells.
So, if I wrote just the element symbol and its atomic mass on the board that students should be able to figure out the number of particles.
Example: Carbon-12
For example, the most common form (isotope) of carbon-12 is written as:
Protons = 6: Since we know the atomic number is 6 (because we memorized it), the atom has 6 protons.
Neutrons = 6 : Since the atomic mass is 12 (upper left of the element symbol), to find the number of neutrons we subtract the number of protons (12 – 6 = 6).
Electrons = 6: This atom is balanced in charge so it needs six electrons with their negative charges to offset the six positive charges of the six protons. (Note: we haven’t talked about unbalanced, charged atoms yet, but the charge will show up as a superscript to the right of the symbol.)
Electron shells (2-4): We have six electrons, so the first two go into filling up the first electron shell, and the rest can go into the second shell, which can hold up to 8 electrons. This gives an electron configuration of 2-4.
Diagram of a carbon-12 atom.
Example: Carbon-14
Carbon-14 is the radioactive isotope of carbon that is often used in carbon dating of historical artifacts. It is written as:
Protons = 6: As long as it’s carbon it has six protons.
Electrons = 6: This atom is also balanced in charge so it also needs six electrons.
Neutrons = 8 : With an atomic mass of 14, when we subtract the six protons, the number of neutrons must be 8 (14 – 6 = 8).
The only difference between carbon-12 and carbon-14 is that the latter has two more neutrons. These are therefore two isotopes of carbon.
Diagram of a carbon-14 atom.
Example: Helium-4
Diagram of helium-4 atom.
Example: Sodium-23
Diagram of sodium-23 atom.
Note: A picture of a hydrogen atom can be found here.
Update: I’ve created an interactive app that will draw atoms (of the first 20 elements), to go with a worksheet for student practice.
This curious video advocates for a new type of nuclear reactor (that runs on thorium) over traditional uranium reactors and chemical fuels. In doing so it gives a useful, but quick, explanation of how energy is produced from these sources.
Dr. Austin has the middle school students build physical models of the continents as an exercise in geography. They use some type of cellulose clay to shape the topography then paint on or apply other icons to represent other types of spatial data; one group, for example, used sparkles to represent population.
The final models are nice for trying stop-motion fly-throughs.
In the early stages of the formation of a solar system, dust in the nebula around a young star is attracted to each other because of their minute gravitational attraction to each other.
In the video below, accumulation of dust and gas creates a planet, probably a gas giant, that clears a swath of the solar nebula.
The Fulton School has a wonderful music program, so I’m hoping that this video, about how Paraguayan children living in a slum on a landfill have recycled classical instruments out of the trash, resonates with some of my environmental science students.
Of course, we’ve seen other instruments invented out of discarded trash. The BBC has a brief history of the steel pan, but Trinbagopan.com has an much more detail. On the other hand, I prefer my history in a musicalform.
Zoe Rodriguez del Rey tried to measure the caffeine concentration in the seawater off Oregon by measuring its concentration in mussels. It’s an interesting measure of just how the stuff we eat and drink can affect the environment. Curiously, del Rey and her colleagues found lower concentrations near the cities’ sewage treatment plants compared to areas further away from the cities.
Scientists sampled both “potentially polluted” sites—near sewage-treatment plants, larger communities, and river mouths—and more remote waters, for example near a state park.
Surprisingly, caffeine levels off the potentially polluted areas were below the detectable limit, about 9 nanograms per liter. The wilder coastlines were comparatively highly caffeinated, at about 45 nanograms per liter.
“Our hypothesis from these results is that the bigger source of contamination here is probably on-site waste disposal systems like septic systems,” said study co-author Elise Granek.
