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Write NO MORE THAN THREE WORDS for each answer．
An apprenticeship is a form of on-the-job training that combines workplace experience and classroom learning．It can last anywhere from one to six years, but four years is typical for most．An apprentice spends the majority of the time in a workplace environment learning the practical skills of a career from a journeyman--someone who has done the job for many years．The rest of the apprentice's time is spent in a classroom environment learning the theoretical skills the career requires．Being an apprentice is a full-time undertaking．
One of the advantages of apprenticeship is that it does not cost apprentices anything．The companies that hire them pay for school．What's more, it offers apprentices an "earn while you learn" opportunity．They usually start out at half the pay of a journeyman, and the pay increases gradually as they move further along in the job and studies．Near the end of the apprenticeship, their wages are usually 90 percent of what a journeyman would receive．Apprenticeship also pays off for employers．It can offer employers a pool of well-trained workers to draw from．
Despite the advantages, apprentices are usually required to work during the day and attend classes at night, which leaves little time for anything else．Sometimes, they might be laid off(下岗)if business for the employers is slow．
Once they have completed the apprenticeship and become journeymen, they receive a nationally recognized and portable certification and their pay also increases again．Some journeymen continue employment with the companies they apprenticed with; others go onto different companies or become self-employed contractors．
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Atoms are building materials of all matter, because by putting together atoms in different ways, all elements and compounds can be formed．
An element is a substance or a kind of thing that has only one type of atom． Pure oxygen has only oxygen atoms． Elements are substances which cannot be broken down chemically into any simpler substances．
All the atoms of an element have the same atomic number． You will remember that the atomic number is the number of protons (= very very small pieces of matter that carry positive or Å electricity) in the nucleus or centre of an atom, and this number determines or decides the nature of the element． Each oxygen atom has eight protons in its nucleus, while each aluminum has thirteen． We call these substances elements because all their atoms are of the same type;they all have the same number of protons in the nucleus．
The element is made up of chemical units which have two or more atoms held together by chemical bonds or connections． A chemical unit is the smallest unit of a substance which shows all the chemical nature of the substance． Chemical units of elements are called molecules． The number of atoms in a molecule depends on the element．
At room temperature, some elements are gases (in a gas, there are larger spaces between the (molecules )． In the Noble Gases, each molecule has only one atom, because the atoms of these elements do not form chemical bonds with each other． In other gases, however, the molecules each have two atoms held together by chemical bonds． For example, nitrogen, chlorine, fluorine, oxygen, and hydrogen are all gases whose molecules have two atoms each．
The chemical symbol or sign of an element stands for one atom of the element． The formula of the element, however, stands for one molecule of the element．
Most elements are solid at room temperature． Some of these elements are made up of single atoms placed closely together within the solid, e．g． copper, iron, and nickel．
Other solid elements are made up of molecules with two or more atoms each． Iodine is a solid whose molecules have two atoms each(I2 ), but phosphorus has molecules made up of four atoms (P4 ), while the molecules of sulphur may have up to eight atoms each ( S8 )． In each of these elements, the molecules are put so closely together that the result is a solid substance．
Bromine and mercury are two elements which are liquids at room temperature． Bromine, like its neighbours chlorine and iodine in the periodic ( = of period ) table, has molecules made up of two atoms each． In these liquid elements, the molecules are close together, but not so crowded;they can pass lightly by one another．
1．All elements are made up of ．
A．atoms B． matter C． building materials D． molecules
2Pure elements can ______．
A．never be broken away in any way
B．not be broken into smaller parts in any simpler way
C．seldom be made up of only one atom
D．have only oxygen atoms
3．Which of the following statements is TRUE?
A．The nature of atoms decides the nature of an element they are in．
B．The number of atoms decides the nature of an element they are in．
C．The nature of protons inside an atom decides the nature of the atom．
D．The number of protons inside an atom decides the number of the atom．
4． The symbol of aluminum is ______ and its atom number is ______
A．Al, 8 B．Alu, 9 C．Al, 13 D．Alu, 14
5． The molecule is ________of a substance．
A．a small chemical unit B．the smallest unit
C．the chemical bonds D．a chemical unit
6． A noble gas molecule has ________．
A．something to do with room temperature
B．no chemical bonds with each other
C．only one atom
D．has no chemical bonds with other elements
7．The formula of fluoride , sulphur , iodine and phosphorus are __________．
A 2, 4, 6, 8 B．2, 2, 4, 8
C．2, 4, 2, 8 D．2, 8, 2, 4
8． Molecules in a solid are those in a gas．
A．as closely placed as B．more closely put than
C．less closely placed than D．smaller in space than
9． It seems that elements in an ordinary lab are solids．
A．mostly B．sometimes C．seldom D．never
10． Which of the following statements is TRUE?
A．Bromine and mercury are always solids．
B．Molecules of liquids are less closely put than those of gases．
C．Each bromine element has the same number of atoms as that of nitrogen．
D．Liquid molecules are always more closely put than those of solids．
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