More Practice Drawing Atomic Structure
You have learned that the simplest model of the atom (the Bohr model) shows protons and neutrons in the nucleus and represents the mass of the atom. Electrons are so much less massive that protons and neutrons that we don’t even include their mass in the total mass of an atom. Whereas the nucleus is vibrating in place, the electrons are moving in layers called shells at 1% the speed of light (300,000 km/s) around the nucleus. That’s fast enough that an electron could travel the circumference of the Earth in less than 20 seconds! Shells represent energy levels around the nucleus where electrons will orbit. Electrons will always fill in shells at the lowest energy level first, so they fill from the innermost shell outward. Although we draw dotted circles around the nucleus to represent shells, they are really spheres since atoms exist in three dimensional space. Putting electrons in their appropriate shells is easy. Just remember to follow the rule that up to 2 electrons can go in the first shell and then it is full, up to 8 electrons can go in the second shell and then it is full, same for the third shell and then up to 18 electrons for shells 4 and 5, and finally up to 32 electrons for shells six and seven. For example Oxygen has 8 electrons. Two go in the first shell and six in the second. If you don't understand this go back and read the page in your binder titled Atomic Structure.
1. Draw the nuclei of the atoms of the first two rows, or periods, using your periodic table. Remember: atomic mass (rounded) – atomic number = neutrons, and the atomic number is the number of protons and (generally) the number of electrons. Remember also that protons and neutrons are packed together tight like a bunch of grapes. If you need more room use binder paper for your answers.
H He
Li Be B C N O F Ne
Now draw a dotted circle around the H and He nuclei and fill in their electrons spaced equally apart. Then draw an inner and outer dotted circle around nuclei Li though Ne and fill in each elements electrons putting two in the inner circle and the rest in the outer circle.
Can you see a pattern emerging for adding electrons? Now draw the nuclei and electrons in their dotted circles, called electron shells, of the third row, or period, of the table. You will draw 3 dotted circles (shells) for each element in the third row and fill electrons like you did above.
Na Mg Al Si P S Cl Ar
Finally, answer the questions below.
1. How many electrons can go in the first shell, the second, the third, the fourth, the fifth, the sixth, and the seventh?
2. Explain why a shell is really a sphere of electrons around the nucleus.
3. How fast are electrons whizzing around the nucleus of an atom? How long would it take for an electrons to circumscribe Earth?
4. Which shell is the lowest energy level? Which shell is the highest?
5. Explain how electrons fill shells.
5. Atoms are mostly empty space. That is due to the distance between the nucleus and the shells of electrons. But if you walk into a wall why don't you walk right through it? Here's a hint: think about the repulsion of like charges when two electrons get near each other they push away.