Subject 3 Elements

Topic 3

elements

1、elements

26 letters that can spell hundreds of thousands of English words . For example, the main components of eggshells, shells and limestone are calcium carbonate, and calcium carbonate is composed of three elements: carbon, oxygen and calcium. Another example, oxygen and carbon dioxide are different in composition and properties, but they all contain oxygen.

Oxygen molecules and carbon dioxide molecules both contain oxygen atoms. The nuclei of these oxygen atoms contain 8 protons, that is, the number of nuclear charges is 8. Chemically, all oxygen atoms with the number of protons are 8 are collectively called oxygen element. Similarly, all hydrogen atoms with a proton number of 1 are collectively referred to as hydrogen elements, and all carbon atoms with a proton number of 6 are collectively referred to as carbon elements. It can be seen that an element is a general term for a class of atoms with the same number of protons.

When a substance undergoes a chemical change, the types of atoms remain unchanged and the elements do not change.

2. Element symbols

It would be very troublesome to express more than one hundred elements and tens of millions of substances composed of them in words.

 Internationally, the first letter (capital) of the Latin name of the element is uniformly used to represent the element, such as the symbol of the hydrogen element is H, and the symbol of the oxygen element is 0 ; If the first letter of the Latin names of several elements is the same, a lowercase letter is added to distinguish them. For example, Cu represents copper element , Cl represents chlorine element, and Ca represents calcium element.

When writing element symbols, it should be noted that for element symbols represented by two letters, the second letter must be lowercase.

An element symbol denotes an element and also denotes an atom of such an element. For example, the element symbol "0" represents both the element oxygen and an atom of the element oxygen.

3. Introduction to the Periodic Table of Elements

There are hundreds of kinds of commodities in the supermarket. In order to facilitate customers to choose and buy, they must be classified and placed in an orderly manner (as shown in Figure 3-22 ) . The material world around us is composed of more than one hundred elements. In order to facilitate the study of the properties and uses of elements, it is also necessary to seek the internal regularity among them. For this reason, scientists

According to the atomic structure and properties of the elements, we arrange them scientifically and orderly, thus obtaining the periodic table of elements.

The periodic table of elements has 7 rows and 18 columns. Each row is called a cycle, and each column is called a group ( the three columns 8, 9, and 10 together form a group).

In order to facilitate the search, the periodic table of elements numbered the elements in the order of increasing nuclear charge, which is called atomic number. The atomic number is numerically the same as the nuclear charge of an element.

On the periodic table of elements, metal elements, non-metal elements and rare gas elements are divided into different colors, and the relative atomic masses of the elements are marked.

The periodic table of elements is an important tool for learning and researching chemistry. Its content is very rich. At present, due to the lack of knowledge we have learned, we cannot fully grasp it, but we can still gain a lot of knowledge from the table.

After studying this topic, you should know

1.In chemistry, an element is a general term for a class of atoms with the same number of protons.

2.Each element is represented by an internationally accepted symbol. Element symbols are an important tool for learning chemistry. When learning chemistry for the first time, it is necessary to memorize and write some common element symbols correctly.

3.The periodic table of elements is an important tool for learning and researching chemistry.