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  • 原子数量和质量数量

    Athletes in colorful jerseys compete in a basketball game, showcasing teamwork and individuality.

    Athletes wearing the same-colored jerseys are all on the same team. In addition, each player’s jersey has a unique number to distinguish him from his teammates. Imagine how confusing it would be if members of both teams wore the same-colored jerseys or all the members of a team had the same number on their jerseys. How could you tell the athletes apart?
    ::穿着同色球衣的运动员都是同一个球队的。 此外,每个球员的球衣都有独特的编号来区分他和他的队友。 想象一下,如果两个球队的成员都穿着同色球衣,或者球衣上的所有队员都有相同的号码,那么,球衣的球衣会有多混乱。 你怎么能分辨运动员的区别呢?

    Telling Atoms Apart
    ::告诉Atoms 公寓

    It’s often useful to have ways to signify different people or objects like athletes on teams. The same is true of atoms. It’s important to be able to distinguish atoms of one from atoms of other elements. Elements are pure substances that make up all other matter, so each one is given a unique name. The names of elements are also represented by unique one- or two-letter symbols, such as H for hydrogen, C for carbon, and He for helium. You can see other examples in the Figure .
    ::以某种方式来表示不同的人或像运动员那样的球队运动员一样的物体往往是有益的。 原子也是如此。 能够将原子与其他元素的原子区分开来是很重要的。 元素是纯物质,构成所有其它物质,因此每个物质都有一个独特的名称。 元素的名称也代表着独特的单字母或双字母符号,如氢的H、碳的C和氦的H。 您可以在图中看到其他例子。

    A periodic table displaying symbols for various chemical elements, including potassium (K) and others.

    Q: The table shown above is called the periodic table of the elements. Each symbol stands for a different element. What do you think the symbol K stands for?
    ::问题:上面的表格被称为元素的周期表。每个符号代表不同的元素。您认为K符号代表什么?

    A: The symbol K stands for the element potassium. The symbol comes from the Latin name for potassium, which is kalium .
    ::A:符号K代表元素钾。符号来自钾的拉丁名,即。

    The symbols in the table above would be more useful if they revealed more information about the atoms they represent. For example, it would be useful to know the numbers of and in the atoms. That’s where atomic number and mass number come in.
    ::上表中的符号如果能揭示更多关于原子的信息,则会更有用。 比如,了解原子的数量和原子的数量。 原子的数量和质量数量就来自原子的数量和数量。

    Atomic Number
    ::原子原子数量

    The number of protons in an is called its atomic number . This number is very important because it is unique for atoms of a given element. All atoms of an element have the same number of protons, and every element has a different number of protons in its atoms. For example, all helium atoms have two protons, and no other elements have atoms with two protons. In the case of helium, the atomic number is 2. The atomic number of an element is usually written in front of and slightly below the element’s symbol, like in the Figure for helium.
    ::质子数被称作原子数。 这个数字非常重要, 因为它是给定元素原子独有的。 一个元素的所有原子都有相同的质子数, 每个元素的原子在原子中都有不同的质子数。 例如, 所有原子都有两个质子, 没有其它元素有两个质子的原子。 在氦的案例中, 原子数是 2 。 一个元素的原子数通常写在元素符号前面, 并且略低于元素符号的原子数, 比如, 的图中 。

    Depicts the atomic number of helium labeled as 2, shown near its element symbol.

    Atoms are neutral in electrical charge because they have the same number of negative electrons as positive protons. Therefore, the atomic number of an atom also tells you how many electrons the atom has. This, in turn, determines many of the atom’s properties.
    ::原子在电荷中是中性的,因为它们的负电子数量与正质子相同。 因此,原子原子的原子数也告诉你原子有多少电子。 这反过来又决定了原子的许多特性。

    Mass Number
    ::质量数量数量

    There is another number in the box above for helium. That number is the mass number , which is the mass of the atom in a unit called the atomic mass unit (amu) . One atomic mass unit is the mass of a proton, or about 1.67 × 10 -27 kilograms, which is an extremely small mass. 
    ::在以上框中,有另外的数。该数字是质量数,即原子在原子质量单位(AMU)中的质量。一个原子质量单位是质子的质量,或大约1.67×10-27公斤,这是一个极小的质量。

    A neutron has just a tiny bit more mass than a proton, so its mass is often assumed to be one atomic mass unit as well. Because electrons have virtually no mass, just about all the mass of an atom is in its protons and neutrons. Therefore, the total number of protons and neutrons in an atom determines its mass in atomic mass units.
    ::中子的质子比质子大一点,因此其质子通常被假定为一个原子质量单位。 因为电子几乎没有质量,所以原子的所有质量都存在于质子和中子之中。因此,原子中的质子和中子总数决定着原子质量单位的质量。

    Consider helium again. Most helium atoms have two neutrons in addition to two protons. Therefore the mass of most helium atoms is 4 atomic mass units (2 amu for the protons + 2 amu for the neutrons). However, some helium atoms have more or less than two neutrons. Atoms with the same number of protons but different numbers of neutrons are called isotopes. Because the number of neutrons can vary for a given element, the mass numbers of different atoms of an element may also vary. For example, some helium atoms have three neutrons instead of two. Therefore, they have a different mass number than the one given in the box above.
    ::再考虑。 大部分原子除了两个质子之外还有两个中子。 因此, 大多数原子的质量是4原子质量单位( 质子为2 amu + 2 amu 中子为2 amu )。 但是, 一些原子的重量或多或少于两个中子。 质子相同但中子数量不同的原子被称为同位素。 由于一个元素的中子数量可能不同, 元素不同原子的质量数量也可能不同。 例如, 一些原子有3个中子, 而不是两个中子。 因此, 它们的质量数量与上面框中给出的数量不同。

    Q: What is the mass number of a helium atom that has three neutrons?
    ::Q:一个有3个中子的氦原子的质量数是多少?

    A: The mass number is the number of protons plus the number of neutrons. For helium atoms with three neutrons, the mass number is 2 (protons) + 3 (neutrons) = 5.
    ::A:质数是质子数加上中子数。对于拥有3个中子的氦原子,质量数为2(质子)+3(中子)=5。

    Q: How would you represent this of helium to show its atomic number and mass number?
    ::问题:你如何代表 来显示它的原子数和质量数?

    A: You would represent it by the element’s symbol and both numbers, with the mass number on top and the atomic number on the bottom:
    ::A: 您可以用元素的符号和两个数字来代表它, 质量数字在顶部,原子数字在底部:

    2 5 He

    ::25He 25He 25He

    Summary
    ::摘要

    • Elements are pure substances that make up all matter, so each one is given a unique name. The names of elements are also represented by unique one-, two-, or three- letter symbols.
      ::元素是指构成所有物质的纯物质,因此每个元素都有一个独特的名称。元素的名称也用独特的一、二、三字母符号表示。
    • The number of protons in an atom is called its atomic number. This is also unique for each element.
      ::原子中的质子数量被称为原子数。 这对于每个元素也是独一无二的。
    • An atom’s mass number is its mass in atomic mass units (amu), which is about equal to the total number of protons and neutrons in the atom.
      ::原子的质数是原子质量单位的质量数,相当于原子质子和中子的总数。
    • Different isotopes of an element have different mass numbers because they have different numbers of neutrons.
      ::元素的不同同位素的质数不同,因为它们的中子数量不同。

    Review
    ::回顾

    1. What is the atomic number of an atom? Why is this number important?
      ::一个原子的原子编号是什么?为什么这个数字重要?
    2. Describe the atomic mass unit. What does it represent and what does it equal?
      ::描述原子质量单位。它代表什么,它等于什么?
    3. The symbol below represents an isotope of helium. How many protons and neutrons does it have?
      ::下面的符号代表的同位素。它有多少质子和中子?

    2 3 He

    ::23HE 23HE 23HHE

    1. All carbon atoms have six protons. Most also have six neutrons, but some have seven or eight neutrons. What is the mass number of a carbon isotope that has seven neutrons?
      ::所有碳原子都有6个质子。大多数也有6个中子,但有些有7个或8个中子。一个碳同位素有7个中子的质量数量是多少?

    Resources
    ::资源