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Atomic Number and Ions Help

By — McGraw-Hill Professional
Updated on Aug 28, 2011

Introduction to Atomic Number and Ions

To understand chemistry and chemical reactions, you have to understand the very basic building blocks of the elements. The protons, neutrons, and electrons are all pretty standard stuff by now. But there are more shortcuts to make the study of chemistry easier. One of them is atomic number.

Atomic Number

The modern Periodic Table contains over one hundred (still a matter of debate) elements. To better describe the central nature of the elements, the atomic number (Z) of the element is used. The atomic number (Z) is determined from the number of protons within the nucleus of an element. Neutrons are not recorded.

Atomic number (Z) gives us information about an element’s character and allows us to balance the total electrical charge in a molecule.

Atomic number (Z) is equal to the number of protons in the nucleus of an atom.

Remember when Mendeleyev’s and Meyer’s first attempts at arranging elements into the Periodic Table pointed to other undiscovered elements? At first, by atomic mass only, they arranged the elements on cards and shuffled them around in order to find the best fit. When elements were finally put into rows (periods) and columns (groups) by greater and greater atomic number, things got clearer.

Then, when they included the place holders they found similar functions and characteristics. Mendeleyev stuck with his intuition when placing cobalt and nickel, as well as tellurium and iodine, switching their places based on activity and character rather than mass only.

Gallium and germanium, discovered one year apart (1875 and 1876), slid into open slots as if Mendeleyev had been waiting for them to show up all along. Maybe he had.

Be careful not to confuse atomic number with atomic weight. Tungsten has 74 protons and its atomic number is 74. The atomic weight of tungsten is 183.85. Hydrogen has a single proton and its atomic number is 1. Lithium has 3 protons, 4 neutrons, and 3 electrons. Its atomic number is 3. Its atomic weight is 6.94. Mendelevium (named after you know who) has 101 protons and 157 neutrons, and 101 electrons. It has an atomic number of 101, but an atomic weight of 258. You get the idea.

Examples

See if you can figure out the following:

(a) What is the name of the element with the atomic number of 86?

(b) What is the name of the element with 37 protons?

(c) How many protons does yttrium have in its nucleus?

(d) What is the name of the element with three more protons than gold?

(e) What is the name of the element with one less proton than vanadium?

Did you get (a) radon, (b) rubidium, (c) 39, (d) lead, and (e) titanium?

When you find atomic number, you find the number of protons too! With this information, you can find a nucleus’s charge. In general, atoms and molecules have equal numbers of electrons and protons and then have no overall charge. They are neutral.

All compounds are neutral and have zero charge. Cations (+) total overall charge = anions (–) total charge.

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