What are atoms?

1. What are atoms? Atoms are the basic building blocks of matter that make up everyday objects. A desk, the air, even you are made up of atoms! There are 90 naturally occurring kinds of atoms. Scientists in labs have been able to make about 25 more.

3. Atoms are composed of protons, neutrons, and electrons. Protons and neutrons are located in a central area called the nucleus. Electrons move about the nucleus. The number of electrons is equal to the number of protons.

4. lithium Electrons move around the nucleus. In a Bohr model of an atom, the electrons are shown moving in concentric circular paths. Each circle represents a different energy level or orbital

5. It is more accurate to represent the space occupied by electrons as a cloud than a circular path. The electrons are likely to be located somewhere within the cloud.

6. These clouds are called “orbitals” (energy levels). Unlike a planet which orbits the sun and whose path is the same from one time to the next, electrons change their “paths” within the cloud. Orbitals are different shapes depending on the number of electrons in an atom - here are some “pictures” of how different orbitals might look:

9. Atomic Symbols AZX notation atomic weight = protons + neutrons atomic number = protons C 12 6

10. C He H 12 4 1 6 2 1

11. Adding atomic parts can change the atom • Adding a proton changes the atom into a new atom with a new atomic number!!! • Adding or subtracting an electron makes an ion of that atom! • Adding a neutron makes an isotope of that atom, a heavier version of that atom!

12. Adding a neutron makes an isotope of that atom, a heavier version of that atom!

15. Particle Accelerators

17. Scientists discovered the neutron and proton in 1932.

19. +

21. Scientists also found quarks inside the neutron. So far they haven’t been able to look inside an electron!

22. What are atoms? Compiled by Sharon King from various web sites - such as Jefferson Labs, Inc, http://education.jlab.org/atomtour/neutron.html