Section outline

  • Colorful fireworks exploding against a dark night sky during a celebration.

    Fireworks are a great way to celebrate happy events. Do you know what causes the brilliant, colored lights of fireworks? The lights are bursts of energy given off by atoms in the fireworks. What do you suppose causes these bursts of light? The answer has to do with energy levels of atoms.
    ::烟花是庆祝欢乐事件的伟大方式。 你知道烟花的亮光是什么原因吗? 灯光是烟花中的原子释放出来的能量。 您认为是什么导致了这些光的暴发? 答案与原子的能量水平有关。

    What Are Energy Levels?
    ::什么是能源水平?

    Energy levels (also called shells) are fixed distances from the nucleus of an where electrons may be found. Electrons are tiny, negatively charged particles in an atom that move around the positive nucleus at the center. Energy levels are a little like the steps of a staircase. You can stand on one step or another but not in between the steps. The same goes for electrons. They can occupy one energy level or another but not the space between energy levels.
    ::能量水平( 也称为贝壳) 是离一个可以找到电子的核心的核心的固定距离。 电子是微小的负电荷颗粒, 在原子的中心周围移动正核。 能量水平有点像楼梯的阶梯。 您可以站在一个或另一个阶梯上, 但不能站在两个阶梯之间。 电子也一样。 它们可以占据一个或另一个能量水平, 但不能占据能量水平之间的空间 。

    The model in the Figure shows the first four energy levels of an atom. Electrons in energy level I (also called energy level K) have the least amount of energy. As you go farther from the nucleus, electrons at higher levels have more energy, and their energy increases by a fixed, discrete amount. Electrons can jump from a lower to the next higher energy level if they absorb this amount of energy. Conversely, if electrons jump from a higher to a lower energy level, they give off energy, often in the form of light. This explains the fireworks pictured above. When the fireworks explode, electrons gain energy and jump to higher energy levels. When they jump back to their original energy levels, they release the energy as light. Different atoms have different arrangements of electrons, so they give off light of different colors. 
    ::图中的模型显示了原子的前四个能源水平。 能源水平I( 也称为能源水平K) 的电能量最少。 当你离核更远时, 高水平的电子拥有更多的能量, 并且它们的能量会以固定的、 离散的数量增加。 如果吸收这种能量, 电子可以从低到下更高的能源水平跳跃。 相反, 如果电子从高水平跳到低能量水平, 它们会释放出能量, 通常以光的形式。 这解释了上面所描绘的烟花。 当烟花爆炸时, 电子获得能量, 并跳到更高的能源水平。 当它们跳回原来的能源水平时, 它们会释放出能量作为光。 不同的原子有不同的电子安排, 因此它们会发出不同颜色的光。

    Diagram illustrating four energy levels around an atom's nucleus and electron distribution.

    Q: In the atomic model Figure , where would you find electrons that have the most energy?
    ::问题:在原子模型图中,你在哪里能找到能量最大的电子?

    A: Electrons with the most energy would be found in energy level IV.
    ::A:能源量最大的电子可在第四级能源中找到。

    Energy Levels and Orbitals
    ::能源水平和轨道

    The smallest atoms are hydrogen atoms. They have just one electron. That one electron is in the first energy level. Bigger atoms have more electrons. Electrons are always added to the lowest energy level first until it has the maximum number of electrons possible. Then electrons are added to the next higher energy level until that level is full, and so on.
    ::最小原子是氢原子。 它们只有一个电子。 一种电子处于第一个能源水平。 大原子拥有更多的电子。 电子总是首先被添加到最低能源水平, 直到它拥有尽可能多的电子。 然后, 电子被添加到下一个更高的能源水平, 直到这个水平达到完全水平,等等。

    How many electrons can a given energy level hold? The maximum numbers of electrons possible for the first four energy levels are shown in the Figure . For example, energy level I can hold a maximum of two electrons, and energy level II can hold a maximum of eight electrons. The maximum number depends on the number of at a given energy level. An orbital is a volume of space within an atom where an electron is most likely to be found. As you can see by the images in the Figure , some orbitals are shaped like spheres (S orbitals) and some are shaped like dumbbells (P orbitals). There are other types of orbitals as well.
    ::给定的能量水平能维持多少个电子?前四个能量水平可能的最大电子数量在图中显示。例如,能量水平I最多能维持两个电子,而能量水平II最多能维持八个电子。最高数量取决于给定能量水平的数量。轨道是原子内一个空间的体积,最有可能发现电子。从图中的图中可以看到,有些轨道的形状像球体(S轨道),有些轨道的形状像哑铃(P轨道),还有其他类型的轨道。

    Comparison of s and p orbitals showing their shapes and electron distribution.

    Regardless of its shape, each orbital can hold a maximum of two electrons. Energy level I has just one orbital, so two electrons will fill this energy level. Energy level II has four orbitals, so it takes eight electrons to fill this energy level.
    ::无论形状如何,每个轨道都最多可以容纳两个电子。 能源水平I只有一个轨道, 所以两个电子将填充这个能源水平。 能源水平II有四个轨道, 所以需要八个电子来填充这个能源水平 。

    Q: Energy level III can hold a maximum of 18 electrons. How many orbitals does this energy level have?
    ::Q: 能源水平三级最多可容纳18个电子。这种能源水平有多少轨道?

    A: At two electrons per orbital, this energy level must have nine orbitals.
    ::A:每轨道有2个电子,这一能量水平必须有9个轨道。

    The Outermost Level
    ::最外层

    Electrons in the outermost energy level of an atom have a special significance. These electrons are called , and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so helium’s only energy level is full. This makes helium a very stable . In other words, its atoms are unlikely to react with other atoms.
    ::原子最外端能源水平中的电子具有特殊的意义。 这些电子被称为 , 它们决定了原子的许多特性。 如果原子最外端能源水平包含尽可能多的电子,那么原子就最稳定了。 例如, 有两个电子, 都在第一个能源水平上。 这种能源水平只能维持两个电子, 因而唯一的能量水平是满的。 这让非常稳定。 换句话说, 它的原子不可能与其他原子发生反应。

    Consider the elements fluorine and lithium, modeled in the Figure . Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I).
    ::氟在最外层能源水平(即能源水平II)上拥有八种电子中的七种。如果再有一个电子能填补其最外层能源水平,它会更稳定。另一方面,锂能在其最外层能源水平(也是能源水平II)上仅拥有八种电子之一。如果它少一个电子,它会更稳定,因为它具有完全外层能源水平(现为能源水平I)。

    The arrangement of valence electrons in fluorine and lithium atoms.

    Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure . When the two elements react, lithium transfers its one “extra” electron to fluorine.
    ::氟和锂由于其等值电子的数量而成为高度反应性元素。 氟将很容易获得一个电子,锂将同样容易放弃一个电子以更加稳定。 事实上,锂和氟将像图所示一样一起反应。 当两种元素反应时,锂将一个“额外”电子转换成氟。

    Electron arrangement in lithium and fluorine atoms during their reaction.

    Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is?
    ::Q: 奈子原子有10个电子。 有多少电子在其最外层的能量水平上? 你认为一个奈子原子有多稳定?

    A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can hold only eight electrons. This means that is outermost energy level is full. Therefore, a neon atom is very stable.
    ::A: 纳米原子在能源一级拥有两个电子,在能源一级拥有其余八个电子,在能源一级只有八个电子。这意味着最外层的能量水平是满的。因此,一个纳米原子非常稳定。

    Summary
    ::摘要

    • Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons may be found. As you go farther from the nucleus, electrons at higher energy levels have more energy.
      ::能量水平(也称为电子贝壳)是离原子核的固定距离,在那里可以找到电子。 随着你距离核更远,高能量水平的电子拥有更多的能量。
    • Electrons are always added to the lowest energy level first until it has the maximum number of electrons possible, and then electrons are added to the next higher energy level until that level is full, and so on. The maximum number of electrons at a given energy level depends on its number of orbitals. There are at most two electrons per orbital.
      ::电子总是首先添加到最低能源水平,直到它拥有最大数量的电子,然后将电子添加到下一个更高的能源水平,直到该水平达到完全水平,等等。 特定能源水平上的最大电子数量取决于轨道数量。 最多每个轨道最多有两个电子。
    • Electrons in the outermost energy level of an atom are called valence electrons. They determine many of the properties of an atom, including how reactive it is.
      ::原子最外层能源水平的电被称作值电子。它们决定原子的许多特性,包括反应能力。

    Review
    ::回顾

    1. What are energy levels?
      ::能源水平是多少?
    2. Relate energy levels to the amount of energy their electrons have.
      ::将能量水平与其电子的能量量相对应。
    3. What must happen for an electron to jump to a different energy level?
      ::电子跳到不同的能量水平 会发生什么呢?
    4. How many electrons can the fourth energy level have? How many orbitals are there at this energy level?
      ::第四个能源水平有多少电子?在这个能源水平上有多少轨道?
    5. An atom of sodium has 11 electrons. Make a sketch of a sodium atom, showing how many electrons it has at each energy level. Infer how reactive sodium atoms are.
      ::钠原子有11个电子。 绘制一个钠原子的草图, 显示它在每个能量水平上有多少电子。 推断有反应的钠原子如何。

    Resources
    ::资源