|Posted by Owell on July 27, 2011 at 10:02 AM|
Molecules and compounds
In this chapter we will learn how compounds are formed, the types of chemical bonds in the compounds, how to write correct formulas and the names of the two types of compounds.
Molecules and compounds
Molecule is a particle of matter, which has two or more atoms chemically combined.
In chapter 3 we learned that pure substances can be classified as elements or compounds. Elements can exist as individual atoms or molecules, the article said. The elements exist as molecules with more than one atom of the same chemical combinations.
A compound consists of two or more items (two or more types of atoms) that have combined chemically, and therefore exists as molecules. Examples of compounds are water, H2O sulfuric acid, H2SO4, carbon monoxide, CO compounds usually have completely different properties to the elements of that form. For example, table salt, NaCl (sodium chloride) is commonly used to make our food taste better, but the sodium metal and chlorine gas can be very dangerous as individual items.
Law of constant composition
In a compound, there are two or more types of atoms present. However, it is important to realize that a compound has a fixed composition, while a mixture of variable composition. The law of constant composition (sometimes called the law of definite proportions) states that a compound is composed of the same elements combined in the same proportion by weight. For example, the water still has eight parts of oxygen for each of the mass of hydrogen.
Chemical formula offers a quick way to describe the composition of compounds by listing the type of atoms present and the number of atoms, the smallest unit of the compound.
In a chemical formula, the types of atoms are 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 command element specifies how many are present. For example, the formula of the compound is ammonia, NH3, ammonia unit containing one 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.
Elements can be atoms or molecules
As noted above, elements can exist in single atoms (atomic elements) or as molecules (the molecular).
Molecular Elements: State of Sevens
There are seven common molecular elements that occur naturally as the two-atom molecules: H2, N2, O2, F2, Cl2, Br2 and I2. If you find these elements in the periodic table, note that from nitrogen, six of these elements form a figure "7". You must remember to add hydrogen in this group to consider the seven elements. This is known as Rule 7.
A molecule with two atoms is called a diatomic molecule. These seven elements are diatomic molecules. You can also have molecular compounds which are diatomic.
Compounds can be molecular or ionic
The compounds can be classified as molecular compounds or ionic compounds.
(. Pronounce "eye'-ons") are ionic compounds composed of ions Ions are atoms or molecules that have a global charge: positively charged ions are called cations (pronounced "Eye-cat'-ons") and negatively charged ions are called anions (pronounced "an eyes-ons"). A molecule that carries a positive or negative overall charge is called a polyatomic ion. Ionic compounds can be recognized as compounds formed by a metal attached to a nonmetal or polyatomic ion containing compounds.
Molecular compounds are those containing only non-metals bonded together, and where there is no polyatomic ions present.
CaCl2 is an ionic compound containing a metal and attached to a metal does not.
NH4NO3 is an ionic compound because it contains at least one polyatomic ion. (More information about polyatomic ions later ...)
NH3 and H2O would be molecular compounds because they contain only non-metallic minerals bonded together and no polyatomic ions.
The smallest unit of a molecular compound is a molecule. In an ionic compound is the molecular units, but there is a series of trusses or other units of the cations and anions, which we call the '"unity formula".
Writing formulas for binary ionic compounds
Binary ionic compounds, as the name suggests, are composed of two parts. How can we write the correct formula for ionic compounds formed between metallic and non metallic? There are 3 stages: remember practicing how to write these formulas.
1. Write the symbol for the cation first, followed by the symbol of the anion. For the ionic compound formed between magnesium and chlorine, write Mg 2 Cl-1.
2. Cruz taxes and the load on the cation becomes the index for the anion and the charge for the anion becomes the subscript for the cation. Thus in the example of magnesium chloride, can be written MgCl 2 -1. Place the positive and negative signs. For magnesium chloride, the formula would MgCl2. (If the index is 1, 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.
4. Although the ionic compound is made up of charged particles, must be connected so that the compound is the general manager of zero, so that the compound is neutral.
Forecast costs ions
The above instructions assume that you know what the charge of an ion will. How would you know?
If the atom loses one or more electrons, there are more protons than electrons in an atom, so that is positively charged, cationic. Positive (+) to load the same number of electrons lost.
If an atom gains one or more electrons, the more electrons than protons, the atom becomes negatively charged anion. The negative (-) charge is equal to the number of electrons gained.
Once again I remind you, an atom loses electrons (s) to form a cation, an atom gains electrons (s) to form an anion.
How can we know how many electrons from one atom to lose or gain? For many elements, it is relatively easy to look at their position in the periodic table. Elements of the group (Group 1A-7A) form a single charge and the group number is the number of electrons in the outer layer of the atom. Atoms take the easiest way to have eight electrons in their shell, they want to lose or gain electrons to more stable electronic configuration of a noble gas, a byte. Atom less than four electrons in its outer shell and an atom loses electrons more than four electrons in its outer shell electrons gain. The four outer electrons atoms prefer to share rather than winning or losing.
The main group ("the" group) elements, the group number is equal to the electrons in the outer shell. Elements of Group 1A lose a valence electron, and is always free of charge, a 2A team loses two electrons and ions to form the office for two and 3A team to lose three electrons to form ions in three payments.
Group 4A elements have a strong desire to lose or gain electrons, but prefer the action, so they do not form stable monatomic ions.
5A-7A electron groups need to acquire the configuration of a stable octet. 5A group needs three electrons, the electrons will win as 3 and -3, and Group 6A Group 7A are -2 -1 form ions.
It is a form of group 1A elements of two ions? No! It will not be stable. It is a form of elements of a group of two ions? No! Not form a stable ion.
Naming Ionic Compounds
Ionic compounds consist of a cation and an anion. Naming ionic compounds from their formulas, only the name of the cation first, followed by the anion. These are the rules for naming cations and anions.
If communication is a type I or Division (Group "A"), the metal, it will be solely responsible, what is meant. It is not necessary to specify the names. While Mg 2 + is simply the magnesium ion.
If Jarjestelmatunnus is a metal type II (these are transition metals that can be more than one possible charge), the name is the name of the metal Jarjestelmatunnus, after charge, expressed as a Roman in brackets. Thus, the appointment of Fe 3 + is called iron (III) and Fe 2 + is called iron (II). You must be clarified by looking at charged anion cation, is connected. In an ionic compound, the costs must be added up to zero when the compound is neutral, has overall responsibility.
If an ion polyatomic Jarjestelmatunnus, you must know its name. Only CATIONIC polyatomic you should be worried is ammonium ion, which is NH4 +.
If the anion is a metalloid, which takes its name from the fall at the end of the element name and adding "s" in its place. Thus, the anion form is called a chlorine anion "chlorine" and is composed of oxygen, "oxide".
If the anion is a polyatomic ion, you must know your name.
Examples of names and formulas of binary ionic compounds
PowerPoint slides slides to help you practice how to write correct formulas and names of binary ionic compounds. Test yourself by choosing the elements of groups 1 to 3 A and form compounds with elements of groups 5-7. Practice writing their names and formulas.
The ions are polyatomic ion composed of two or more ingredients. These ions are formed when molecules gain or lose electrons. Examples of polyatomic ions, their formulas, charges and the electron-dot structures have been described in the slides. You should be able to identify and name the following polyatomic ions: ammonium (CATIONIC polyatomic only important in this course), acetate, carbonate, hydrogen carbonate (also known as baking soda), hydroxide, nitrate, nitrite, sulfate, and chlorate.
Writing formulas and names of ionic compounds with polyatomic ions
You can write a formula for ionic compounds with polyatomic ions, is to follow the same procedure described above monatomic ions. Write a cationic charge and the first, then the anion, and then download crossover payments. If the index is written in polyatomic ions must be done as the unit and enclosed in brackets, the index is written. Subscript indicates the index of each atom polyatomic ions. Examples are shown compounds formed between Na and SO42- Na2SO4, Fe 3 + and NO3- Fe (NO3) 3
Naming binary molecular compounds
Remember that the molecular compounds are composed solely of non-metals, it is important to remember that molecular compounds containing polyatomic ions such as ammonia. If ammonia is part of the name element (or NH4 + is in the form of the compound), which is an ionic compound, although there is no metal in the compound.
Naming molecular compounds that are 3 simple rules to follow:
1. Name the first nonmetal in the formula, using the full name of the item.
2. The name of the second element of the surface of the skin, but changed its name to the end-ide.
3. Use the prefix in front of each name to tell how many atoms of each element of the sub-indices are combined as in the formula. Use 1 = mono, di-= 2; tetra tri = 3 = 4, etc. (Exception: Do not use "mono" in front of the first element of the name). Prefixes for the top eight from memory.
Example: Boron trifluoride BF3 would be named, diphosphorus pentoxide P2O5.
Determining the mass formula
In the previous chapters, we have appointed the average mass of one atom of an element that the atomic mass atomic mass units (amu). When we speak of the compounds, we define the mass formula as the sum of the atomic masses of each atom in a unit of the formula of an ionic compound or molecular formula of a molecular compound.