The National Science Digital Library has a wealth of high quality digital resources to teach almost any topic in K-12 math and science.  Following is a sample of 20 exemplar NSDL links specific to teaching atomic structure at the K-12 level.

The History of the Atom

1. Atomic Structure Timeline  This site explores discoveries related to atomic structure including the electron, proton and neutron.  Starting with the Greek era (Democritus) until the mid-20^th century, the timeline covers 37 scientists’ work. The site also links to original papers in chemistry.
2. Atomic Theory I: The Early Days and Atomic Theory II: Ions, Isotopes and Electron Shells  Atomic Theory I introduces J. J. Thomson’s discovery of the electron and E. Rutherford’s planetary model of atomic structure.   Atomic Theory II explains the presence of ions, isotopes and discusses N. Bohr’s theory on the quantum behavior of electrons.

Reference Material

1. An Introduction to Chemistry: Structure of Matter PowerPoint  This 45-page PowerPoint presentation uses atomic models to help novice learners visualize the structure of solids, liquids, and gases as matter composed of tiny particles in constant motion. As the lesson progresses, the author explores subatomic particles to explain how the periodic table is organized, and concludes with a brief discussion of ions and isotopes.
2. Atoms and Light Energy  At this site students are reminded of the structure of the atom and the meaning of the terms atom, element, atomic mass, atomic number, and isotope. The Bohr Model is used to review the energy levels, ground state, excited state and ionization. Absorption and emission along with the resulting energies are covered along with the quantum mechanical nature of atoms and photons. The site also includes three student exercises and links for more information.

Tutorials

1. Molecular Logic: Atomic Structure (SAM)  Download this interactive, scaffolded activity that allows students to build an atom within the framework of a newer orbital model. It opens with an explanation of why the Bohr model is incorrect and provides an analogy for understanding orbitals that is simple enough for beginners. As changes are made, the model displays the atomic number, net charge, and isotope symbol.
2. Teachers’ Domain: The Atom  In this Flash interactive activity learners follow the tutorial to understand how individual atoms-the basis of all matter-are composed of subatomic particles such as electrons, protons, and neutrons. They investigate the three types of particles, their properties (such as mass and charge), and relative locations.
3. An Introduction to Chemistry: The Structure of the Elements  This interactive animation gives students a taste of atomic/molecular structure by exploring four elements: oxygen, neon, bromine, and iodine. These elements represent four very different structures — a noble gas (neon), a diatomic gas molecule (oxygen), a diatomic liquid molecule (bromine), and a diatomic solid molecule (iodine). Each element is represented in illustrations and animations that model the molecular motion.
4. Annenberg Learner Interactives: The Periodic Table  This web site introduces the periodic table and the basics of atomic structure within a framework of interactive activities. It takes the learner on a journey to understand the modern orbital model of the atom. It progresses to illustrated tutorials that explore the organization of the Periodic Table, characteristics of isotopes and ions, and how the placement of electrons determines the atomic composition of an element. Throughout are game-like simulations: build an atom by dragging virtual electrons into orbitals, explore ionic bonding by dragging individual ions to create a compound, calculate an atom’s average relative mass with scaffolded help, and more.

Simulations

1. Models of the Hydrogen Atom  How did scientists figure out the structure of atoms without looking at them? Learners try out different models by shooting light at the atom and check how the prediction of the model matches the experimental results.
2. PhET Simulation: Build An Atom  This simulation is designed to help learners visualize atomic structure, as they drag protons, neutrons, and electrons to construct an atom. As particles are moved into place, the simulation automatically displays the net charge, mass number, atomic symbol, and name of the element.  These is a  lesson plan developed specifically to accompany the PhET simulation PhET Teacher Ideas: Build An Atom - Lesson Plan.  The lesson contains a complete student guide in printable pdf format, and pre-lab/post-lab assessments.
3. PhET Simulation: Neon Lights & Other Discharge Lamps  This interactive simulation allows users to understand atomic excitations due to electron scattering. The user can set the voltage of the electrodes in a simulated discharge tube and view the energy level transitions and spectra of photons emitted from atoms excited by the electrons in the tube.

Questions and Activities

1. Atomic Structure and the Periodic Table  17 WebCT exam/quiz questions that focus on the various aspects of the electronic structure of atoms.  Correct answers are included and explained.
2. Atomic Structure Webquest  This web page outlines a student activity on atoms and the periodic table. The assignment includes instructions about how to write a children’s book for 3rd and 4th graders on the topic of the elements. It is a performance-based activity designed to promote critical thinking about atomic and molecular structures as students characterize and model the structures in a storybook format. Grading rubrics are also included.

Periodic Tables

1. Periodic Table Live!  This interactive resource allows learners to explore a broad range of information about the elements and their reactions, properties, structures, and histories. Click on any element to view its description, physical properties, and selected properties of its atomic structure.
2. Chemical Elements.com  This is an online interactive periodic table of the elements which includes all elements up to 118. There are several different options for viewing, such as date of discovery, electron configuration, number of neutrons, etc. Elements can also be viewed by element groups.

For more advanced learners

1. Atomic Structure and the Periodic Table  This section of the online textbook “Chem 1 Virtual Textbook” on General Chemistry is designed to provide a thorough, in-depth treatment of this topic with a special focus on the underlying concepts.
2. Primer on Quantum Theory of the Atom  This question-and-answer tutorial provides an introduction to quantum theory and the electron structure of the atom. This “quantum catechism” presents the basic concepts in an easily understood way and with a minimum of mathematical detail.
3. Rutherford Scattering  How did Rutherford figure out the structure of the atom without being able to see it? Simulate the famous experiment in which he disproved the Plum Pudding model of the atom by observing alpha particles bouncing off atoms and determining that they must have a small core.
4. Why Doesn’t the Electron Fall into the Nucleus?  This tutorial offers a conceptual and non-mathematical answer to this question. The explanation covers the application of quantum theory and points out that a particle such as an electron cannot be treated as a classical particle; discusses the balance between the electron’s kinetic and potential energy; and points out the impossibility of determining simultaneously the precise location and momentum of an electron. The tutorial is part of a virtual textbook for a full-year General Chemistry course.
5. Atomic Spectra  In this Flash animation the user can view the atomic emission spectra (400-700nm) of eight different elements. A dragable marker allows the user to approximate the wavelength of the various spectral lines. The effect of resolution can be examined in the sodium spectrum in the region 550-600nm.