This yr, I've been basing my introduction to basic chemistry for my center school students around the periodic table of the elements. The get-go step, nevertheless, is to teach them how to draw bones models of atoms.

Prep: Memorization over the Wintertime 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 flake of context, I went over the basic parts of an atom (protons, neutrons, and electrons) and fabricated it clear that the name of the chemical element is adamant solely by the number of protons. I fifty-fifty 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 grade catamenia, it probably was a bit much, simply since it was just to give them some context I did not expect the 7th graders, who had non seen this before, to call up it all; for the 8th graders information technology should have been merely a review.

Most students did a skilful task at the memorization. Some found songs on the the internet that helped, while others simply pushed through. Having the ii weeks of winter intermission to work on information technology probably helped too.

Day 1. Lesson: The Parts of an Cantlet

When we got dorsum 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 chemical element names.

Template for the kickoff xx elements of the periodic tabular array. (pdf)

After they'd filled out their periodic table template, I went into the parts of the atoms in more detail, and had them do. The cardinal points I wanted them to recollect 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 — just they could as well expect 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 aforementioned number of electrons equally protons. Protons are positively charged, and electrons are negatively charged, then an atom needs to have the same number of both for its charge to be balanced. We don't talk about ions –where in that location are more or less electrons– until afterwards.
  • The atomic mass (four) 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 (two).

    The small atoms that we're looking at tend to accept the same number of neutrons every bit protons, but that's not necessarily the example. So how practise you know how many neutrons? Y'all have to ask, or look at the atomic mass number, which is usually written to the upper left of the atom. Since the diminutive mass is the sum of the number of protons and neutrons, if yous know the atomic mass and the number of protons, you tin 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 cantlet has viii 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 (two for the first shell; 8 for the 2nd trounce; and viii for the third). And to draw the atoms yous fill upwardly the inner shells beginning so move on to the outer shells.

So, if I wrote just the chemical element symbol and its diminutive mass on the board that students should be able to effigy out the number of particles.

Instance: Carbon-12

For example, the most common form (isotope) of carbon-12 is written as:

  • Protons = 6: Since we know the diminutive number is half dozen (because we memorized it), the atom has vi protons.
  • Neutrons = vi : Since the atomic mass is 12 (upper left of the element symbol), to observe the number of neutrons nosotros subtract the number of protons (12 – six = 6).
  • Electrons = six: This atom is balanced in accuse then it needs half-dozen electrons with their negative charges to start the half dozen positive charges of the half-dozen protons. (Note: we haven't talked about unbalanced, charged atoms yet, just the charge will show up as a superscript to the right of the symbol.)
  • Electron shells (2-four): We accept 6 electrons, and so the first two go into filling up the start electron shell, and the residue tin can become into the 2nd trounce, which tin can hold up to 8 electrons. This gives an electron configuration of 2-4.
Diagram of a carbon-12 atom.

Case: Carbon-fourteen

Carbon-14 is the radioactive isotope of carbon that is ofttimes used in carbon dating of historical artifacts. Information technology is written as:

  • Protons = 6: As long as it's carbon it has vi protons.
  • Electrons = 6: This atom is also counterbalanced in charge so information technology also needs vi electrons.
  • Neutrons = 8 : With an diminutive mass of fourteen, when we subtract the six protons, the number of neutrons must be 8 (14 – 6 = 8).

The only difference between carbon-12 and carbon-xiv is that the latter has two more neutrons. These are therefore ii isotopes of carbon.

Diagram of a carbon-14 cantlet.

Instance: Helium-iv

Diagram of helium-four atom.

Example: Sodium-23

Diagram of sodium-23 cantlet.

Note: A picture of a hydrogen atom can exist found here.

Update: I've created an interactive app that will draw atoms (of the start 20 elements), to go with a worksheet for student exercise.