Isotopes and Atomic M ass. The terms…. The atom: smallest piece of matter with a distinct identity and is used to make up compounds and molecules. Sub-Atomic Particles: Atoms themselves are made of three types of matter. They are the: Proton….small, very heavy, postive charge
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Isotopes and Atomic Mass
All atoms are put together in a regular pattern. All have protons and electrons, and almost all have neutrons.
Protons are in the middle, packed into a very small area called the nucleus
Neutrons also fit into the nucleus
The electrons fill up the rest of the volume of the atom in a large “cloud-like” volume.
The nucleus has almost all the mass, but a very small volume
The electrons have almost no mass, but make up almost all the volume
For atoms, the number of protons determines the number of electrons.
Almost all atoms have neutrons (except Hydrogen, the smallest). The number of neutrons is about the same or up to 50% more than the number of protons.
The chemical properties of an atom depend on how the number of electrons and how they are arranged.
The mass of the atom depends almost entirely on the number of protons and neutrons.
* Realtive mass is based on 1 atomic mass unit (amu) = 1/12 the mass of carbon-12
** Charge is relative to each other. Absolute charge is +/- 1.60218 Coulombs
Atomic Number (Z) = Number of protons
Also equal to the number of electrons (for an atom)
This determines the identity of the atom.
ALL ATOMS WITH THE SAME ATOMIC NUMBER CHEMICALLY ACT THE SAME WAY
Z = p = e(atom)
Mass Number (A) = Number of protons plus the number of neutrons
A = p + n
Every element, (and there are 118 so far discovered), has a defined atomic number. All atoms with that atomic number (and so protons and electrons) is an example of that element.
Because all atoms of that element have the same number of electrons, they chemically behave in exactly the same way.
The number of neutrons may be different between different atoms, but that does NOT change their chemical identity.
Atoms are labeled to identify the element and isotope. Atomic number and mass number are used, in addition to the atomic symbol.
The number of neutrons can be calculated by subtracting the atomic number from the mass number