You will need

- - handle;
- paper;
- - the periodic system of elements.

Instruction

1

To correctly write the structural formula of a chemical substance you should be familiar with and to imagine what is the ability of atoms to form a certain number of electron pairs with other atoms. Because the valence will help you to draw chemical bonds. For example, given the molecular formula of ammonia is NH3. You have to write structural formula. Consider the fact that hydrogen is monovalent always, so its atoms can not be linked, therefore they will be connected with the nitrogen.

2

To correctly write the structural formula of organic compounds, repeat the main provisions of the theory of A. M. Butlerov, according to which there are isomers – substances with the same elementary composition but different chemical properties. For example, isobutane and butane. The molecular formula they are the same: C4H10 structural – differ.

3

In a linear formula, each atom is written separately, so that the image takes up a lot of space. However, when drawing structural formulae, you can specify the total number of hydrogen atoms at each carbon atom. And between neighboring carbons draw the chemical bonds as lines.

4

Writing start with isomers of hydrocarbons of normal structure, i.e. unbranched chain of carbon atoms. Then reduce one atom of carbon, which connect to another internal carbon. Having exhausted all the spellings of isomers with a given chain length, reduce it by one carbon atom. And again connect it to the internal carbon atom of the chain. For example, the structural formula of n-pentane, isopentane, tetramethylsilane. Thus, the hydrocarbon with the molecular formula C5H12 has three isomers.

Useful advice

For determining the valency of atoms when drawing structural formulas use the periodic system. Show the exact distance of the atoms in the molecule will help the three-dimensional structural formula.

# Advice 2 : In Excel enter the formula

Widespread program Excel from Microsoft indispensable for the preparation of tables, charts, calculations. To automate the calculation entered in table cells values in Excel apply the formula. There are certain rules for entering formulas in tables.

You will need

- is Excel installed on the computer.

Instruction

1

Install purchased or download and install the trial version of Excel. Run the program. Consider the interface of the program. The formula bar is denoted by the letters fx. To enter a simple formula into cell enter the required values by putting before them the equal sign. For example, to calculate the sum 1+1 in the cell you need to enter "=1+1" without the quotes and press Enter. In cell will be the result of an accumulation - 2.

2

Use another input method. Click on the empty cell (A1) and paste the number, prefixing it with the sign "equal". In the neighboring cell (B1) insert another number, and so on, depending on how many numbers you need. In the last empty cell put the equal sign.

3

Select the cell A1. Then paste the arithmetic sign (addition, multiplication, division and other) and select another cell such as B2. Press Enter. Examine the original

**formula**, double-clicking on the cell, pressing Ctrl+apostrophe. In addition, the formula appears in the formula bar on the toolbar after selecting the cell. Press F2 to edit the formula and press Enter.4

Add in

**a formula**parentheses to specify the order of execution of the operation. First, the program performs calculations inside parentheses. If brackets is not enough, Excel will give an error - fix.5

To multiply, put the number, then the multiplication sign * is a different number. Excel treats the work of another number, standing to the right. If the number to the left or right is omitted, then the program will generate an error. To add, subtract or divide numbers, use the signs +, -, /.

6

Raise to a power using the ^ character, for example, "=2^3". Degree can be written in other way, for example, "=DEGREE(2;3)". Press Enter. The result will be equal to eight. To find the percentage of a number, multiply the number by n% (n%, the percentage must be calculated).

7

To add up all the numbers from either column, enter in the formula bar

**the formula**"=SUM(A:A)" (this example sums the numbers from column A). To calculate a value, enter in the formula bar "=average(A1:B4)" (in example calculates the average of the values in the range A1 to B4).8

To view the complicated functions, go to the menu tab "Insert" (select "Function" and the function of the categories) or click the "Feature" in recent versions of Excel.

Useful advice

In Excel, if you enter a formula into a cell it automatically substitutes the result of calculations. But sometimes it is necessary to see the formula behind the value of a specific cell and then have to go back to it, and it's not always convenient for complex calculations with lots of formulas. To switch the operation mode to the formulas and calculation results, press [Ctrl]+[~].

# Advice 3 : How to write in Excel formula

Programmable table calculator Excel from Microsoft helps you organize your data and make any calculations, however complicated they may be. To automate the calculations, we need special rules to insert into a table cell of the formula.

Instruction

1

Open Excel by double-clicking on its icon. Carefully consider the interface opened the program and find the line marked with the letters fx. To enter a simple

**formula**, click on an empty cell. Enter to the selected cell of the first equal sign (=), then the required values. Press Enter. For example, to calculate what is the sum 5+2, type in a cell "=5+2" without the quotes and press enter. In the cell the result will appear — 7.2

If you want to add up the cell values, click on the empty cell (A1). Enter the number with a preceding number sign of equality. In cell B1 enter another number. In cell C1 put "=" sign and select cell A1.

3

Type the arithmetic sign (the operator) addition, multiplication, division, or other mathematical operation signs. Select cell B2. Press Enter. Please note that the number of cells is not limited. To view

**the formula**, double click with the left mouse button on the cell and press Ctrl+apostrophe (Russian e).4

If you need to specify a sequence of actions, enclose

**the formula**in parentheses. In long formulas with lots of parentheses, if you forget to put one of them, Excel will display an error message. Fix it — enter the missing parentheses.5

To multiply the number 1 by the number 2 insert in an empty cell the number 1, press the multiplication sign (*) and enter the number 2. The number should be and must be right, otherwise the program will fail. Use arithmetic signs to perform mathematical operations with numbers. For exponentiation, use the ^ character, e.g. "=3^2". Also record the degree formula "=DEGREES(2;3)". After pressing Enter in both cases you will see the result — 9.

6

Limit used in the formula text quotes from both sides. For example, the erroneous formula "=Peter" should look like "="Peter"". To combine text of two cells, write in an empty cell

**the formula**=1&2, where 1 and 2 — cells (A1, A2, B1, B2, and so on).7

Enter in the formula bar "=SUM(A:A)" to add up all the numbers from the given column A. the Column can be changed. Type in "=average(A1:B6)", to calculate the average value in the range from A1 to B6.

8

To insert a complex function, open the "Insert" → "Function", and select from suggested categories or select "Feature" in recent versions of Excel.

# Advice 4 : How to write graphic formulas

In the graphical (structural) formulas the electron pair forming the bond between atoms, indicated by a dash. Graphic

**formulas**give a visual representation of the order of connections between atoms of matter and is particularly widely used in organic chemistry. Hydrocarbons with the same set of atoms may differ in the structure of molecules. These differences reflect the structural**formula**.Instruction

1

Consider the procedure for compiling the graphical

**formula**by the example of phosphate of magnesium. Its chemical formula is Mg3(PO4)2. First draw the structural formula for phosphoric acid that formed the salt. To do this, define the valence of phosphorus in H3PO4. Hydrogen is a donor of electrons, it is monovalent. Oxygen is the electron acceptor, it has a valence equal to 2. Therefore, four oxygen molecules attach eight electrons. Three of them produces hydrogen, the other five or phosphorus. Consequently, the phosphorus is pentavalent.2

Write the symbol for phosphorus. Want to draw five lines indicating the electronic communication. Three of them take the group –OH. There remain two dashes and one atom of oxygen with which the phosphorus and connected by a double bond.

3

Then make the graphic formula of the phosphate of magnesium. In the molecule of salt three atoms of metal associated with two acidic residues. Write a three line symbol for magnesium. Magnesium is divalent - each character should move by two dashes. In the molecule of salt, the magnesium displaces the hydrogen of the acid and rises to take his place. Each acidic residue takes three. To check yourself, count the number of atoms in the resulting structural formula. It must match the number of atoms in the chemical formula.

4

In organic chemistry when writing graphic formulas decided not to designate communication with the hydrogen atoms. The figure shows examples of such structural formulas of organic compounds.