## Composition of matter

### Gap-fill exercise
Study material: Maritime Transportation, Chemistry and Oil_oer.pdf
Test generated using the freeware software provided by Hot Potatoes (version 6). http://hotpot.uvic.ca/

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
Protons and neutrons are the subatomic particles forming the nucleus. The bears +1 elementary electrical charge, the same but negative the , and the carries no charge.
are neutral as a consequence of having the same number protons and electrons; in fact the order in the periodic table depends on this number, called . A related term is , which is the total number of protons and neutrons in the atom.
Atoms with different number of neutrons and the same atomic number, known as , are considered to be the same elements; isotopes distinguish by its , e.g., oxygen-16 (O-16), oxygen-18 (O-18). Natural elements are mixture of the corresponding isotopes, commonly used atomic masses are a of their atomic masses according to their natural abundance.
The is an ordering based on the atomic number as well as their reactivity, which is related with the number of electrons in the different shells, mainly in the more external (the shell).
Although the unified atomic mass unit (
), is the mass unit used to express atomic masses, usually it is easy to handle mass of elements in grams, then the term enters in scene, which is the number of atoms in exactly 12 grams of carbon-12, such number being known as the ’s constant.