文档介绍：化工与环保
Subject English for
Chemical Engineering and Environmental Protection
Contents
I. Chemistry
II. Chemical Technologies
III. Environmental Protection
IV. Scientific Writing
Matter
Mixtures
Pure substances
Heterogeneous
Homogeneous
Elements
pounds
Lect. One Elements pounds
Elements are pure substances that cannot
be posed into simpler substances by ordinary chemical changes
At present time there are 109 known elements.
mon elements that are familiar to you are carbon, oxygen, aluminum, iron, copper, nitrogen, and gold.
The elements are the building blocks of matter just as the numerals 0 through 9 are the building blocks for numbers.
To the best of our knowledge, the elements that have been found on the earth prise the entire universe.
About 85% of the elements can be found in nature, bined with other elements
Copper, Silver, gold, and about 20 other elements can be found in highly pure forms. Sixteen elements are not found in nature; they are man-made elements.
Pure posed of two or
more elements are pounds.
Compounds exist either as molecules which consist of two or more elements bonded together or in the form of positive and negative ions held together by the attractive force of their positive and negative charges.
Compounds
pounds
pounds
pounds
Water is a colorless, odorless, tasteless liquid that can be changed to a solid, ice, at 0 ℃ and to a gas, steam, at 100 ℃. It posed of two atoms of hydrogen and one atom of oxygen per molecule.
pound carbon monoxide (CO) posed of carbon and oxygen in the ratio of one atom of carbon to one atom of oxygen.
Compounds consisting of ions do not exist
as molecules. Sodium chloride is an example of a non-pound. Although this type pound consists of large numbers of positive and negative ions, its formula is usually represented by the simplest ratio of the atoms in pound. Thus, the ratio of ions in sodium chloride is one sodium ion to one chlorine ion.
pounds
Mixtures are formed simply by blendin