Chemistry: exploring the atom, the ion, and isotopes

Atoms are composed of subatomic particles called protons neutrons and electrons.  Protons have a positive charge, neutrons a neutral charge and electrons a negative charge.  The mass number of an element is the number of protons and neutrons in the nucleus of the atom.  The atomic number of an element is the number of protons in the nucleus.  If you subtract the atomic number from the mass number you can determine the number of neutrons in the atom.  The number of electrons is equal to the number of protons in an atom. Electron shells are shown by the letter n.  The shell nearest the nucleus with the lowest energy is n=1, then n=2, and n=3 and so forth.   The first electron shell around the nucleus of an atom has 2 electrons and the second shell can have up to  8 electrons.  The third shell also can have up to  8 electrons.  The fourth shell can have 18 electrons. 

Ions are atoms that gain or lose electrons.  If they gain an electron, they have a negative charge because they have more electrons than protons.  If they lose an electron they have a positive charge because they now have more protons than electrons.  Remember, electrons have a negative charge and protons have a positive charge.

Isotopes are atoms that have the same number of protons and electrons, but different number of neutrons.  The element remains unchanged, however, the mass changes.  Every element has isotopes.  Unstable isotopes decay over time, turning into another isotope.  Unstable isotopes are radioactive.  Stable isotopes do not decay over time and are not radioactive.

Below, under resources, there are additional websites that have information about atoms, if you are interested in learning more, or reviewing what we learned today!

Concluding assessment activity:
Using an index card, pick an element from the periodic table and write the element symbol on your card. It would be best if you choose elements near the top of the table.   Write down the atomic number and the mass number.  Write down the number of protons, neutrons and electrons.  Lastly, draw a rough model of what you think the atom looks like.  Include the electron shells and nucleus.  Please turn this in as you leave.  If you need more time, you may bring it with to the next class period/block.