Chemistry - A Molecular Science

Chapter 1 The Early Experiments

1.11

CHAPTER SUMMARY AND OBJECTIVES Early scientists used the scientific method to

study the chemical and physical properties of

matter. Their experiments led to the classification of pure substances as elements or compounds. Initially, they identified atoms as very small spheres characterized by mass. By the early 20th century, scientists had arrived at the nuclear model of the atom. In this model, the atom has a very small, dense,

positively charged nucleus that contains the

protons and neutrons and is orbited by even

smaller, negatively charged electrons. The

number of protons in the nucleus, which is

the atomic number, characterizes the atom,

while the number of electrons that surround

the nucleus dictates the

charge on the species.

If the number of electrons exceeds the number of protons, the substance is negatively charged and called an anion. If the number of

protons exceeds the number of electrons, the

species is positively charged and called a cation.

The periodic table is one of the greatest classifying systems in science. It orders

logically a great deal of information about an element’s chemical and physical properties, such as its atomic number, whether it is a meta

l, nonmetal, or metalloid, and the ease with

which it undergoes chemical reaction.

After studying the material presented in this chapter, you should be able to: 1. explain the scientific method (Section 1.1); 2. distinguish between atoms, molecules, el

ements, and compounds (Sections 1.2 - 1.4);

3. determine molar mass of elements and com

pounds and determine the number of moles

present in a sample (Section 1.5);

4. define kinetic energy and potential energy (Section 1.6); 5. use Coulomb’s law to explain how the energy

of two particles varies with the charge of,

the distance between, and the medium that separates them (Section 1.7);

6. describe the experiments that

led to the discovery of the

electron and to the determination

of its charge and mass (Section 1.8);

7. describe the nuclear atom and the experime

nts that led to its discovery (Section 1.8);

8. list the common subatomic particles with

their mass numbers and charge; distinguish

between atomic number (Z) and mass number (A

); and determine the number of protons,

neutrons, and electrons in an ion or atom (Section 1.9); and

9. describe the meaning of all numbers and symbols given on the periodic table and

determine whether an element is a metal, nonmet

al, or metalloid from its position on the

periodic table (Section 1.10).

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