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Atomic Basics
Atomic Basics
All atoms (except Hydrogen-1) consist of 3 subatomic particles: protons, neutrons, and electrons.
Together, protons and neutrons are called nucleons.
Atoms are tiny; their radii are on the order of ten billionths of a meter (10–10 m).
Atoms are mostly empty space, with virtually all the mass in the nucleus.
If an atom was an empty American football field, the nucleus would be the size of a pea!
Protons and neutrons are inside the nucleus, while electrons are in energy levels (shells) surrounding the nucleus.
Discovery of the Atom History
Discovery of the Atom History
Human understanding of the atom has changed over time, with the contributions of various scientists and improved technologies.
John Dalton – Billiard model
J.J. Thompson – Plum pudding model
Ernest Rutherford – Empty space model
Niels Bohr – Planetary model
Erwin Schrödinger and Werner Heisenberg – Quantum model
Actual vs Relative Masses of Particles
Actual vs Relative Masses of Particles
Actual masses and charges of subatomic particles are given in Data Booklet #2. These have been determined by experimentation.
The mass of an electron is so tiny, it is considered negligible.
Relative masses and charges are often more meaningful and useful.
Describing an Element
Describing an Element
Changes in Numbers - Ions
Changes in Numbers - Ions
Cation: a positively charged ions (one or more electrons have been lost)
Anion: a negatively charged ion (one or more electrons have been gained)
Ions can be written with ionic symbols
Examples:
Ca2+ → has 20 protons and 18 electrons
2 electrons have been lost to give it a +2 charge
F– → has 9 protons and 10 electrons
1 electron has been gained to give it a –1 charge
When Neutrons Differ…Isotopes
When Neutrons Differ…Isotopes
Isotopes are atoms with the same number of protons, but a different number of neutrons.
How do properties of isotopes (of the same element) compare to each other?
Chemical properties (how the elements participate in reactions) are effectively the same, as these are determined by electrons, and the number of electrons are the same.
Physical properties (boiling point, melting point, density, etc.) are different, as these are determined by atomic masses, which are different with differing neutrons.
Example 1: Hydrogen has 3 isotopes
Physical properties differ: 16O water cat is less dense than 18O water cat.
Heavy Water in a Nuclear Reactor
Heavy Water in a Nuclear Reactor
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