Learning Activity Sheet 2 Activity No. 2: Crossword Puzzle: Atomic Models in Focus Across Electrons exist in specific energy levels as a cloud 8. Electrons reside in orbits. They move between each shell when gaining or losing energy 9. Negatively charged particles 10. Building block of matter that cannot be broken apart using any chemical means. Down 1. An atom is made up of a sphere of positive charges with negatively charged electron embedded in it. 2. Subatomic particle with a neutral charge 3. A tangible model 5. Matter is made of small indivisible atoms 6. Most of the mass is concentrated in the center of the atom. 7. Positively charged particles ​