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Molecules and Molecular Formula Help (page 2)

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By — McGraw-Hill Professional
Updated on Aug 28, 2011

Molecular Formula

A molecular formula is more specific than a compound’s name. It gives the exact number of different atoms of each element in a molecule. We saw this earlier in the formula of water, H 2 O.

Think of it as a closer look, like being shown the difference between a long-bed truck and an 18-wheel truck/trailer combination. The components are basically the same, engine, tires, body, and frame, but the number of wheels and length can make all the difference in the size and function of the vehicle.

In Table 5.2 you will see some common molecular formulas.

A simple formula such as CuSO 4 gives the number of atoms of the different elements in the sample.

A molecular formula is more specific. It gives the exact number of different atoms of each element in a molecule. Water is written as H 2 O, saltpeter (used in fireworks and fertilizer) is KNO 3 , and fructose (the sugar found in fruit and honey) is C 6 H 12 O 6 .

Table 5.2 Molecular formulas show the number of atoms present in a molecule.

Atoms, Elements, and Compounds Molecular Formula

An element is composed of the same kinds of atoms, chemically bonded by attractive forces. These atoms are usually held together in a certain way. Within a specific element, its atoms combine in certain ways with its own atoms, as well as those of other elements. This bonding comes about because of the properties of electrons and their location around each atomic nucleus.

Structural formulas show how specific atoms are ordered and arranged in compounds.

Think of it like a football game. The plays are set up with different players placed in certain positions. Each play is designed to serve a particular purpose. If the players form up one way, the quarterback may throw the ball. Set up in another way and the end player runs the ball over and across. If the players on the other side don’t react to a certain configuration in the predicted way, the quarterback may have to run the ball. Placement and function of individual players is everything in football.

The same is true of chemistry. The arrangement of the atoms in a molecule can make a big difference in the characteristics and reactivity of compounds.

Figure 5.4 shows structural formulas with individual elements indicated. A structural formula shows exactly how an element is connected to the others in the molecule. Researchers study the structure of a molecule to figure out how it will react in a reaction. Structure has a definite effect on the properties of compounds. Knowing compounds’ structures and their bonding abilities will make it easier to understand how molecules do what they do.

Atoms, Elements, and Compounds Molecular Formula

Fig. 5.4. Structural formulas of different compounds make it easier to see how atoms are bonded.

Practice problems for these concepts can be found at - Atoms, Elements, and Compounds Practice Test

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