Wednesday, July 27, 2011

Molecules and Compounds

Molecules and compounds


Molecules and compounds

A molecule is a particle of matter in which two or more atoms chemically combined.

Chapter 3, we know that pure substances can be classified as elements or compounds. The elements can occur in individual atoms or molecules, depending on the item. Elements that we are molecules with more than one atom of the same type of chemically combined.


Law of constant composition


Chemical formulas


In a chemical formula, atom types represented by the symbol of the element of the periodic table. If more than one atom of a particular type is present, an index number to the right of the symbol of the element indicates how many are present. For example, the formula NH3 ammonia compound, an ammonia unit contains a nitrogen atom and three hydrogen atoms. If only one atom of a particular type, the index "1" is not used. Use parentheses around a group of atoms in a formula to repeat.

Articles may be atomic or molecular


Molecular Elements: State of Sevens

There are seven common elements at the molecular level, which occurs naturally as two atoms molecules: H2, N2, O2, F2, Cl2, BR2, and I2. If you find one of these factors, the periodic table, you will find that nitrogen starts, six of these elements form the number "7". You must remember to add hydrogen to this group accounts all seven elements. This is called the rule of 7, about

Two atoms, molecules called diatomic molecule. These seven blocks diatomic molecules. You can also molecular compounds which are diatomic.

The compounds can be molecular or ionic

The compounds can be classified as molecular compounds or ionic compounds.

(. Pronounced "eye'-ons") are ionic compounds composed of ions Ions are atoms or molecules that have a total charge: positively charged ions are called cations (pronounced "cat-eye-ons") and negatively charged ions are called anions (pronounced "eye-an'-ons"). A molecule that carries an overall positive charge or negative is called a polyatomic ion. Ionic compounds can be recognized as compounds that consist of a metal tied to a metal or non-compounds containing polyatomic ions.

Molecular compounds are those that contain only non-metals are glued together, and where there are polyatomic ions are present.

CaCl2 is an ionic connection because it contains a metal bound to a non-metal.


NH3 and H2O would be molecular compounds because they contain only non-metallic minerals bonded to each other and there is no polyatomic ions.

The smallest unit of a molecular compound is a molecule. In an ionic compound, there is no molecule units, but there is a matrix or network of repeating units of cations and anions, which we call a "unit of the formula."

Writing formulas for binary ionic compounds

Binary ionic compounds, as its name suggests, consists of two elements. How to write the correct formula for ionic compounds formed between a metal and non metal? There are three steps, you will remember them by practicing how to write formulas.


2. Payments crossover so that the cationic charge should be the index for the anion and the anion of the payment should be the index for the cation. So, for example, magnesium chloride write -1 Mg Cl 2. Drop the positive and negative signs. For magnesium, the formula would then MgCl2. (If the index is 1, it is not written.)

3. Reduction and simplification, so that the indices are the smallest whole relationships. For example, ionic compound formed between calcium and sulfur, Ca +2 and S-2 ® ® Ca2S2 Cas.

Although the fourth of a connection consisting of ionic charged particles, they must be together in such a way that the substance has a total charge of zero, so that the substance is neutral.

Predicting the costs of the ions

The above instructions assume you know what the charge on an ion. How do you know?

If an atom loses one or more electrons, the more protons than electrons in the atom, therefore, become positively charged cations. The positive (+) charge is equal to the number of electrons lost.


Once again to help you remember, one atom loses electron (s) to form a cation, an atom gains electron (s) to form an anion.


For the division (Group "A") information, the group number corresponding to the number of electrons in the outer layer. Group 1A elements will lose their valence 1 and will always be fresh, Group 2A lose 2 electrons to form ions with the two group leaders and 3A will lose 3 electrons to form ions with the three leaders.

4A group elements have a strong desire to lose or gain electrons, but prefer the action, so no stable monatomic ions.



Naming ionic compounds



If communication is a metal type II (these are transition metals that may have more than one office), the name of the cation is the name of the metal freight tracking, expressed in Roman numerals in parentheses. Thus, naming Fe3 + will be called iron (III) and Fe 2 + will be called iron (II). You must determine the load on the anion cation watching is paired with. In connection ionic charges build up to give zero, so that the compound is neutral, it will have a global responsibility.

If the communication is a polyatomic ion, you must know its name. The only polyatomic cation you should be worried about is the ammonium ion, which is NH4 +.

If the anion is a non-metal, he was appointed by the fall of the end of the item name and add "-ide" in its place. Thus, the anion formed by the element chlorine called "chloride" anion and oxygen is formed by "oxide".


Sample forms and names of binary ionic compounds


Polyatomic ions.

Polyatomic ions are ions composed of two or more items. These ions are formed when molecules gain or lose electrons. Examples of polyatomic ions, forms, fees and structures of electron pairs are illustrated in the slides. You should be able to recognize and name the following polyatomic ions: ammonium (cation polyatomic only of importance in this course), acetate, carbonate, bicarbonate (aka baking soda), sodium hydroxide, nitrates, nitrites, sulfates and chlorates.

Writing formulas and names of ionic compounds with polyatomic ions


Naming binary molecular compounds

Remember that the molecular compounds are composed solely of non-metals, it is important to remember that the molecular compounds do not contain polyatomic ions such as ammonium. If ammonia is part of the name of the item (or NH4 + in the compound of formula) is an ionic connection, although there is no metal in the compound.

Naming molecular compounds that are 3 simple rules to follow:

First name of non-metals, first in the formula, using the full name of the item.


Use a third prefix to each name to tell how many atoms of each element in the compound as indicated by the index in the formula. Use mono = 1 di = 2 tri = 3 tetra = 4, etc. (Exception: Do not use "mono" to the name of the first element.) Prefixes for numbers one through eight must be memorized.

Example: BB-3 would be designated as boron trifluoride, there would diphosphorus P2O5.

Determination of the Mass Formula



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