chemical formula

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THE CHEMICAL FORMULA Neil Jozsef C. Macion Kristi Mari N. Montefalcon Maria Angelica Fatima Navarro

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Page 1: Chemical Formula

THE CHEMICAL FORMULA

Neil Jozsef C. MacionKristi Mari N. MontefalconMaria Angelica Fatima Navarro

Page 2: Chemical Formula

What is Chemical Formula?......

Chemists use Chemical Formula to express the composition of molecules and ionic compounds in terms of chemical symbols. By composition we mean not only the elements present but also the ratios in which the atoms are combined. Here we are mainly composed of two formulas : Molecular formulas and Empirical formulas.

Page 3: Chemical Formula

Structural Formula

The structural formula of a chemical compound is a graphical representation of the molecular structure, showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly.

Example:

H2OThe structural formula of water is

HH O

The structural formula is important is important for it helps us in making the Ball-and-stick model

Page 4: Chemical Formula

Molecular formulas

The molecular formula shows the exact number of atoms of each element n the smallest unit of a substance.

Example:

H2 is the molecular formula for Hydrogen

O2 is the molecular formula for Oxygen

H2O is the molecular formula for Water

The subscript numeral indicates the number of atoms of an element present. There is no subscript for O in H2O because there is only one atom of oxygen in a molecule of water, and so the number “one” is omitted in the formula.

Page 5: Chemical Formula

Molecules are too small for us to observe directly. An effective means of visualizing them is by the use of molecular models. Two standard types of molecular models are the Ball-and-stick models and the Space-filling models.

Molecular Models

Page 6: Chemical Formula

Ball-and-stick Model

In chemistry, a ball-and-stick model is a molecular model of a chemical substance which aims to display both the three-dimensional position of the atoms and the bonds between them.

The atoms are typically represented by spheres

And are connected by rods which represent the bonds.

Page 7: Chemical Formula

Space-filling model

In chemistry, a space-filling model, also known as calotte model, is a type of three-dimensional molecular model, where the atoms are represented by spheres whose radii are proportional to the radii of the atoms, and whose center-to-center distances are proportional to the distances between the atomic nuclei, all in the same scale.

Here’s an example of a space filling model of Cyclohexane (C6H12)

Page 8: Chemical Formula

Example

Write the molecular formula for methanol, an organic solvent and anti freeze, from its ball-and-stick model, shown in the margin.

Solution:There are four H atoms, one C atom, and one O atom. Therefore the molecular formula is CH4O. However, the standard way of writing the molecular formula for methanol is CH3OH because it shows how the atoms are joined in the molecule.

Answer: CH3OH

Page 9: Chemical Formula

QUIZ!!!!

Page 10: Chemical Formula

1. Write the molecular formula of chloroform, which is used as a solvent and a cleansing agent. The ball-and-stick model of chloroform is shown in the margin.

Page 11: Chemical Formula

2. Write the molecular formula of glycine, an amino-acid present in protiens. The color codes are: Black(carbon), blue (nitrogen), red (oxygen), and gray (hydrogen).

Page 12: Chemical Formula

3. Write the formula of ethanol. The color codes are: black (carbon), red (oxygen), and gray (hydrogen).

Page 13: Chemical Formula

ANSWER KEY

1. CHCl3

2. C2H5NO2

3. C2H6O

Page 14: Chemical Formula

Empirical formula

The Empirical formulas are the simples chemical formulas; they are written by reducing the subscripts in the molecular formulas to the smallest possible whole numbers. The empirical formula of hydrogen peroxide is HO. Thus the empirical formula tells us which elements are present and the simplest whole-number ratio of their atoms, but not necessarily the actual number of atoms in a given molecule.

Page 15: Chemical Formula

In finding the Empirical formula you divide the molecular formula with its greatest common multiple until it will be simplified.

Example:

C2H8

We search for the greatest common multiple in this formula

Which is 2 so we will divide the formula by 2 So the Answer will be

CH4

8/2 = 4

2/2 = 1

Page 16: Chemical Formula

Although there are some exceptions to other formulas.

Example:

Mn2O3

In this equation you noticed that this formula has a odd or prime number

If the equation cannot be simplified you will just copy it for there is no fraction or decimal in the molecular formula of atoms

Page 17: Chemical Formula

Example

Write the example of the following molecules:

(a)Acetylene (C2H2)

(b) glucose (C6H12O6), a substance known as blood sugar; and

(c) (N2O), a gas that is used as an anesthetic gas and as an aerosol propellant for whipped creams.

Page 18: Chemical Formula

Answers

(a) CH

(b) CH2O

(c) N2O

Page 19: Chemical Formula

Solution

(a)There are two carbon atoms and two hydrogen atoms in acetylene. Dividing the subscripts by 2, we obtain the empirical formula CH.

(b) In glucose there are 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Dividing the subscripts by 6, we obtain the empirical formula CH2O. Not that if we had divided the subscripts by 3, we would have obtained the formula (C2H4O2). Although the ratio of carbon to hydrogen to oxygen atoms in C2H4O2 is the same as that in C6H12O6 (1:2:1), C2H4O2 is not the simplest formula because its subscripts are not in the smallest whole number ratio.

(c) Because the subscripts in N2O are already the smallest possible whole numbers, the empirical formula for nitrous oxide is the same as its molecular formula.

Page 20: Chemical Formula

!!!QUIZ!!!

Page 21: Chemical Formula

1. What are the empirical formula of the following compounds:

(a) C2N2

(b) C6H6

(c) C9H20

(d) P4O10

(e) B2H6

(f) Al2Br6

(g) Na2S2O4

(h) N2O5

(i) Kr2Cr2O7

Page 22: Chemical Formula

Answers

(a) CN(b) CH(c) C9H20

(d) P2O5

(e) BH3

(f) AlBr3

(g) NaSO2

(h) N2O5

(I ) Kr2Cr2O7