Atomic Number and Ions Help

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?

(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.

Ions

If an atom or molecule gains or loses one or more electrons, it is no longer neutral and becomes a charged ion . ( Note: protons cannot change to become ions, only electrons.) Ions are charged elements with complete orbitals following the octet rule. They are unbalanced electrically, highly attracted to ions of the opposite charge, and eagerly stick together to form ionic compounds.

Research has found that most of the transition metals form more than one kind of ion with unique charges. Iron (Fe) forms two different ions, Fe ²⁺ and Fe ³⁺ , and nickel forms Ni ²⁺ or Ni ³⁺ . Cobalt (Co ²⁺ , Co ³⁺ ), copper (Cu ⁺ , Cu ²⁺ ), tin (Sn ²⁺ , Sn ⁴⁺ ) and lead (Pb ²⁺ , Pb ⁴⁺ ) also exist in more than one ion form.

Monatomic Ions

These ions are very simple, single ions that have a positive or negative charge. Monatomic ions can have fixed charges like hydrogen (H ⁺ ), cesium (Cs ⁺ ), sulfide (S ⁻ ), and nitride (N ³⁻ ) or variable charges like copper (Cu ⁺ , Cu ²⁺ ), gold (Au ⁺ , Au ³⁺ ), and tin (Sn ²⁺ , Sn ⁴⁺ ). A good number of elements found in nature have had many different ion forms isolated.

Polyatomic Ions

When two or more atoms are covalently bonded, but keep an overall charge, they are known as polyatomic ions . Polyatomic ions are groups of atoms with an overall electrical charge. The majority of these ions are single element atoms bonded with oxygen. The element name is taken from the innermost or core atom. The single most common positive polyatomic ion is the ammonium ion Atomic Number and Ions Polyatomic Ions . Positive polyatomic ions have a charge because the combined atoms from the two combining elements have lost one or more electrons.

Figure 9.1 shows a few monatomic and polyatomic cations and their charges.

Atomic Number and Ions Polyatomic Ions

Fig. 9.1. Monatomic and polyatomic cations have specific charges.

Most of the common inorganic (no carbon) polyatomic ions have negative charges. The phosphate ion, Atomic Number and Ions Polyatomic Ions , has an overall negative charge as does the oxalate ion, .

Table 9.1 lists some common monatomic and polyatomic anions (–).

Polyatomic ions have two or more atoms held together by a covalent bond, but they still have an overall charge.

One way to recognize and study polyatomic ions and their specific elements is through their names. Chemical name endings are used with the idea of telling more about an ion’s characteristics.

Practice problems for these concepts can be found at – Atomic Number and Ions Practice Test

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Atomic Number and Ions Help

Introduction to Atomic Number and Ions