| WORDS TO KNOW |
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| DEFINITIONS |
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| Atomic mass |
The average mass of the naturally occurring isotopes in the sample of an element |
| Atomic mass unit |
A unit equal to 1/12 the mass of a carbon-12 atom |
| Atomic number |
The number of protons in the nucleus of an atom |
| Cathode-ray tube |
Two metal electrodes in an evacuated glass tube |
| Coulombs |
The unit for measuring electric charge |
| Electrons |
Negatively charged particles that have very little mass but take up most of the space in an atom; found orbiting outside the nucleus of the atom |
| Energy level |
Any of the various levels in the shell model of the atom where electrons are found |
| Isotopes |
Atoms of the same element that have different numbers of neutrons |
| Mass number |
The total number of protons and neutrons in the nucleus of an atom |
| Molecular mass |
The sum of the atomic masses of the atoms in a molecule |
| Neutrons |
Particles that have no charge and have a slightly greater mass than a proton; located inside the nucleus |
| Protons |
Positively charged particles that have more than 1800 times the mass of an electron, but take up very little of the volume of the atom; located inside the nucleus |
| Valence electrons |
The electrons in the highest energy level in the shell model of an atom |
500 Words
