How To Draw An Atom Of An Element

This year, I've been basing my introduction to basic chemical science for my center school students around the periodic table of the elements. The showtime step, however, is to teach them how to draw basic models of atoms.

Prep: Memorization over the Winter Interruption

I started it off past having the students memorize the first 20 elements (H through Ca), in their correct order — by diminutive number — over their winter break.

Oxygen-shells — A diagram of an oxygen cantlet.

So that they'd accept a fleck of context, I went over the bones parts of an atom (protons, neutrons, and electrons) and made information technology articulate that the name of the element is determined solely past the number of protons. I even had them draw a few atoms with the protons and neutrons in the middle and the electrons in shells. Since I'd dumped all of this on them in a single class catamenia, it probably was a chip much, only since information technology was just to give them some context I did non await 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 likewise.

Twenty-four hour period one. Lesson: The Parts of an Cantlet

When we got back to school, the kickoff thing I did was requite them an outline of the upper part of the periodic table and asked them to fill information technology in with the element names.

Later on 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 call up 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 club, they should be able to figure this out on their own — but they could besides look it up apace 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 every bit 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 in that location are more or less electrons– until later.
The diminutive mass (iv) is written every bit a superscript to the left of the chemical 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 yous know how many neutrons? Y'all have to ask, or look at the atomic mass number, which is ordinarily written to the upper left of the atom. Since the atomic mass is the sum of the number of protons and neutrons, if you lot know the atomic mass and the number of protons, you can hands effigy out the number of neutrons. (Notation 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 eight electrons in two shells.

Electron Shells: Electrons orbit effectually the nucleus in a series of shells. Each crush can concur a sure maximum number of electrons (2 for the first beat out; 8 for the 2nd shell; and 8 for the third). And to draw the atoms you make full the inner shells first then motility on to the outer shells.

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

Example: Carbon-12

For example, the most common class (isotope) of carbon-12 is written every bit:

Protons = 6: Since we know the atomic number is 6 (considering nosotros memorized it), the atom has vi 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 = six: This atom is balanced in accuse and then 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 all the same, but the charge volition show upward every bit a superscript to the right of the symbol.)
Electron shells (2-four): We accept vi electrons, and so the beginning two get into filling upwardly the beginning electron shell, and the rest can go into the second trounce, which can agree up to 8 electrons. This gives an electron configuration of 2-4.

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 = half dozen: As long equally it's carbon it has six protons.
Electrons = six: This cantlet is also counterbalanced in charge so it also needs six electrons.
Neutrons = 8 : With an atomic mass of fourteen, when we subtract the six protons, the number of neutrons must be 8 (fourteen – half-dozen = 8).

The simply difference between carbon-12 and carbon-xiv is that the latter has two more than neutrons. These are therefore 2 isotopes of carbon.