Quantum Mechanical Model of single Lithium Atom.

MODELS PRINTED IN COLOR ON GLOSSY,

110# CARD-STOCK PAPER READY TO BE

CUT OUT BY STUDENTS

Tools needed for cutting out and assembling lithium atom model.

• Scissors.
• 1/4” single-hole punch.
• Cellophane tape for repairs.

Useful for: HS-PS1-1. Use periodic table as a model to predict the relative properties of elements based on the patterns of elections in the outermost energy.

1. The lithium model is a physical representation of the mathematical equations that define the quantum mechanical model of lithium.
2. The model shows the first and second energy levels (shells), sub-levels, and the orientations of orbitals within them.
3. The first energy level displays two core electrons as red ovals. (The color red refers to cars being stopped and not able to go at traffic lights. Therefore core electrons cannot leave the atom as indicated by red.)
4. The outermost energy level (second energy level for lithium) has one valence electron with a green oval. (Cars can go on green at traffic lights. Valence electrons can go, or leave the atom as indicated by green.)
5. This model can be dismantled so that the orbitals can be placed on an orbital diagram which is available from Quanta to Galaxies. The symbol for an electron, core or valence, in an orbital diagram is an arrow. The electrons in the model are not real, but they are a step closer to reality than written symbols and help to understand what the arrows and other symbols in orbital diagrams and electron configurations represent.
6. Quantum mechanics requires that all atoms are both neutral and stable. Neutrality is accomplished with number of electrons being equal to number of protons. Stability is accomplished when the outermost energy level is filled with electrons, or totally empty. This means two electrons for hydrogen and helium and eight electrons for all other atoms (octet rule).
7. The lithium model displays three protons in the nucleus and three electrons in the first and second energy levels. Therefore, it is neutral. (Since neutron numbers vary they are not shown in these models. There are lessons available specifically about isotopes! that deal with variation neutron numbers.)
8. Lithium has one valence electron in its outermost energy level and seven empty holes that could hold electrons. Thus lithium is not stable as presented by this model. If the one valence electron, which can be removed from the hole, is taken out, the entire second energy level is left with eight empty holes. The empty second energy level orbitals can be removed leaving a lithium with two electrons in the first energy level, now the outermost energy level. This leaves the new structure stable.
9. With only two electrons the lithium may be stable, but it is no longer neutral. The challenge will be for students to solve the neutrality problem and still keep lithium stable. (Hint: introduce a fluorine atom into the lesson! and discuss formula units and/or molecules.)

This lithium atom model can be used with other atom models from periods 1, 2, 3, and 4 to analyze periodic trends.

Also useful for: PS1.A: Structure and Properties of Matter

As noted already, the model provides a three dimensional display of the structure of the lithium atom which is relevant to NGSS standard PS1.A: Structure and Properties of Matter and provides the following:

1. A great hands-on manipulative for classroom activities that can engage the student in active learning with more material retained.
2. Hands-on learning environment that develops critical thinking.
3. Use of materials and equipment.
4. A model that is a step or two closer to reality than printed text or drawings.
5. A lesson that sometimes is just more fun.

Some teachers have already reported to us that the models have stimulated conversations among students relevant to the proposed lesson before the teacher even begins to interact with the students.

Completion of the physical model has been reported to give many students a sense of pride in being able to do more than read and respond. Parents have reported that some of the students have kept and displayed their model for as many as ten years after graduation.

And useful for: MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structure.

The lithium model can be used with fluoride to demonstrate that an ionic compound such as salt is more than an organized structure made up of plain, solid spheres.