Chemical formulas covalent compounds

Types of Chemical Formulas Ionic Compounds Binary Covalent Compounds Alkanes... 

Phosphine is a covalent compound of phosphorus, P, and hydrogen, H. What is its chemical formula ... 

For covalent compounds, the chemical formula represents how many of each type of atom are in each molecule. For example, the formula NH3 signifies that a molecule of ammonia contains one nitrogen atom and three hydrogen atoms. The formula C2H6 tells you that a molecule of propane contains two atoms of carbon and six atoms of hydrogen. 

You have seen how Lewis structures can help you draw models of ionic, covalent, and polar covalent compounds. When you draw a Lewis structure, you can count how many electrons are needed by each atom to achieve a stable octet. Thus, you can find out the ratio in which the atoms combine. Once you know the ratio of the atoms, you can write the chemical formula of the compound. Drawing Lewis structures can become overwhelming, however, when you are dealing with large molecules. Is there a faster and easier method for writing chemical formulas ... 

You can use valences to write chemical formulas. This method is faster than using Lewis structures to determine chemical formulas. As well, you can use this method for both ionic and covalent compounds. In order to write a chemical formula using valences, you need to know which elements (or polyatomic ions) are in the compound, and their valences. You also need to know how to use the zero sum rule For neutral chemical formulas containing ions, the sum of positive valences plus negative valences of the atoms in a compound must equal zero. 

The ability to name compounds and determine the chemical formula for a compound comes from the ability to distinguish between ionic and covalent compounds. The name of a compound depends heavily on the type of bond present between the atoms. Besides being able to identify certain types of bonds, when learning to name compounds it is best to remember the rules that apply to the type of bond in question. The rules for naming four common kinds of compounds are outlined below. 

The forces that hold atoms together in compounds are called chemical bonds. One way that atoms can form bonds is by sharing electrons. These bonds are called covalent bonds, and the resulting collection of atoms is called a molecule. Molecules can be represented in several different ways. The simplest method is the chemical formula, in which the symbols for the elements are used to indicate the types of atoms present, and subscripts are used to indicate the relative numbers of atoms. For example, the formula for carbon dioxide is C02, meaning, of course, that each molecule contains 1 atom of carbon and 2 atoms of oxygen. 

This difference between empirical formula and chemical formula (known for covalent compounds as the molecular formula) becomes important when we look at organic chemistry. (See Module 6.)... 

You know that many atoms covalently bond to form molecules that behave as a single unit. These units can be represented by chemical formulas and names that are used to identify them. When naming molecules, the system of rules is similar to the one you used to name ionic compounds. 

How do we name nonionic (covalent) compounds If a pair of elements forms only one compound, begin with the name of the element that appears first in the chemical formula, followed by the second element, with the suffix -ide added to its root. This is analogous to the naming of ionic compounds. Just as NaBr is sodium bromide, so the following names designate typical covalent compounds ... 

Now that you understand chemical formulas, you can look back at the other chemical compounds shown earlier in this chapter, and write their chemical formulas. A water molecule contains one oxygen atom and two hydrogen atoms, so its formula is H2O. Ammonia, shown in Figure 22, is a covalent compound that contains one nitrogen atom and three hydrogen atoms. Its chemical formula is NH3. 

Toothpaste Ingredients Examine the ingredient label on a tube of toothpaste. Write formulas for as many of the chemical names listed as you can. List whether each ingredient is an ionic or a covalent compound. 

As you know, the chemical formula of a compound tells you the elements that comprise it. For example, the formula for geraniol (the main compound that gives a rose its scent) is CjoHigO. The formula shows that geraniol is comprised of carbon, hydrogen, and oxygen. Because all these elements are nonmetals, geraniol is probably covalent and comprised of molecules. 

Because the ratio of moles is the same as the ratio of atoms, CH2O is the empirical formula for this compormd. But, the empirical formula is not always the chemical formula. Many dilferent covalent compounds have the same empirical formula, as demonstrated in Figure 12.11, because atoms can share electrons in different ways. 

The formulas of the chemical compounds are no accident. There is an NaCl, but no NaCl2 there is a Cap2, but no CaF. On the other hand, certain pairs of elements form two, or even more, different compounds, e.g. C]u20, CuO N2O, NO, NO2. In the case of ionic compounds the relative number of positive and negative ions in a formula is governed simply by the rule of electrical neutrality. In covalent compounds, or within polyatomic ions (like NO ), structures are formed by covalent bonds (i.e., electron sharing). A hierarchy of covalent bonding theories exists, of which the simplest, the drawing of Lewis structures, is emphasized in this and in most elementary texts. 

We can probably assume that tbe parent who wrote this note meant the child was taken to the doctor for an injection, but who knows Like everyone else, chemists need to be careful about how they use language, and the names and formulas for chemical compounds form the core of the language of chemistry. The purpose of this section is to describe the guidelines for constructing the names for binary covalent compounds, which are pure substances that consist of two nonmetallic elements. The water, H2O, you boil to cook your eggs and the methane, CH4, in natural gas that can he burned to heat the water are examples of binary covalent compounds. 

Now let s go the other way and convert from systematic names to chemical formulas. The first step in writing formulas when given the systematic name of a binary covalent compound is to recognize the name as representing a binary covalent compound. It will have one of the following general forms. 

Follow these steps for writing formulas for binary covalent compounds when you are given a systematic name. Notice that they are the reverse of the steps for writing names from chemical formulas. 

Convert between the systematic names and chemical formulas for binary covalent compounds. 

The compound represented by the hall-and-stick model to the left is used in the processing of nuclear fuels. Although bromine atoms most commonly form one covalent bond, they can form five bonds, as in the molecule shown here, in which the central sphere represents a bromine atom. The other atoms are fluorine atoms. Write this compound s chemical formula and name. List the bromine atom first in the chemical formula. 

Given a name or chemical formula, tell whether it represents a binary ionic compound, an ionic compound with polyatomic ion(s), a binary covalent compound, a binary acid, or an oxyacid. 

Convert between names and chemical formulas for binary ionic compounds, ionic compounds with polyatomic ion(s), binary covalent compounds, binary acids, and oxyacids. 

Names and formulas of compounds form the vocabulary of the chemical language. In this discussion, you ll learn the names and formulas of ionic and simple covalent compounds and how to calculate the mass of a unit of a compound from its formula. 

Chemical formulas describe the simplest atom ratio (empirical formula), actual atom number (molecular formula), and atom arrangement (structural formula) of one unit of a compound. An ionic compound is named with cation first and anion second. For metals that can form more than one ion, the charge is shown with a Roman numeral. Oxoanions have suffixes, and sometimes prefixes, attached to the element root name to indicate the number of oxygen atoms. Names of hydrates give the number of associated water molecules with a numerical prefix. Acid names are based on anion names. Covalent compounds have the first word of the name for the element that is leftmost or lower down in the periodic table, and prefixes show the number of each atom. The molecular (or formula) mass of a compound is the sum of the atomic masses in the formula. Molecules are depicted by various types of formulas and models. 

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