Atomic and ionic radius · 原子半径与离子半径
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| atomic radius/əˈtɒmɪk ˈreɪdɪəs/ | 原子半径 | yuán zi bàn jìng |
| nuclear charge/ˈnjuːklɪə tʃɑːdʒ/ | 核电荷 | hé diàn hè |
| shielding/ˈʃiːldɪŋ/ | 屏蔽 | píng bì |
| cation/ˈkætaɪən/ | 阳离子 | yáng lí zi |
| anion/ˈænaɪən/ | 阴离子 | yīn lí zi |
| isoelectronic/ˌaɪsəʊlɪkˈtrɒnɪk/ | 等电子 | děng diàn zi |
How big is an atom?
- The atomic radius 原子半径 is the size of an atom.
- It changes in a clear pattern across the Periodic Table.
- Ions have their own sizes too.
原子有多大?
- 原子半径(atomic radius) 是一个原子的大小。
- 它在周期表中以一个清晰的规律变化。
- 离子也有它们自己的大小。
A positive ion (cation) is smaller than its parent atom. · 一个正离子(阳离子)比它的母原子小。
Losing the outer-shell electrons reduces shielding and shrinks the ion. · 失去外壳层电子减少了屏蔽,使离子变小。
Across a period and down a group
- Across a period (left → right), the radius gets smaller. The nuclear charge 核电荷 rises but shielding 屏蔽 stays about the same, so the outer shell is pulled in.
- Down a group (top → bottom), the radius gets larger. Each step adds a new shell, with more shielding.
Atomic radius shrinks across a period (stronger pull on the same shell) and grows down a group (new shells)
沿周期和沿族
- 沿一个周期(左 → 右),半径变 小。核电荷 升高但屏蔽几乎不变,所以外壳层被拉进来。
- 沿一个族向下(上 → 下),半径变 大。每往下一步增加一个新 壳层,屏蔽更多。
原子半径沿周期减小(对同一壳层拉力更强),沿族向下增大(新壳层)
Atomic and ionic radius trends · 原子半径与离子半径的趋势
Atomic radius falls across a period (rising nuclear charge pulls the same shell in) and rises down a group (an extra shell each time). Step across Period 3 to see it. · 原子半径沿一个周期减小(升高的核电荷把同一壳层拉进来),沿一个族向下增大(每次增加一个壳层)。沿第 3 周期一步步看。
Across a period, the atomic radius decreases because: · 沿一个周期,原子半径减小,因为:
Electrons go into the same outer shell, so rising nuclear charge with similar shielding pulls them closer. · 电子进入同一个外壳层,所以升高的核电荷加上相近的屏蔽把它们拉得更近。
Down a group, the atomic radius increases because: · 沿一个族向下,原子半径增大,因为:
Adding shells increases distance and shielding, so the radius grows down a group. · 增加壳层增大了距离和屏蔽,所以半径沿一个族向下增大。
Match each change to its effect on radius. · 把每个变化与它对半径的影响配对。
Pulling power vs number of shells sets the size; ions differ from their atoms by the electrons gained or lost. · 拉力与壳层数目决定大小;离子与它们的原子相差所得失的电子。
Ion sizes
- a cation 阳离子 (positive ion) is smaller than its atom — it has lost its outer shell.
- an anion 阴离子 (negative ion) is larger than its atom — extra electrons repel each other.
- among ions with the same number of electrons, the one with more protons is smaller.
A scanning tunnelling microscope can image individual atoms
离子的大小
- 阳离子(cation)(正离子)比它的原子 小——它失去了外壳层。
- 阴离子(anion)(负离子)比它的原子 大——多出的电子互相排斥。
- 在 电子数相同 的离子中,质子更多 的那个 更小。
扫描隧道显微镜能给单个原子成像
Compared with its atom, a cation (positive ion) is: · 与它的原子相比,一个阳离子(正离子)是:
Losing the outer shell (and electrons feeling a stronger pull each) makes a cation smaller than its atom. · 失去外壳层(且每个电子感受到更强的拉力)使阳离子比它的原子小。
Among ions with the same number of electrons, the smallest is the one with the most ______. · 在电子数相同的离子中,最小的是 ______ 最多的那个。
More protons pull the same number of electrons in more tightly, giving a smaller ion. · 更多的质子把相同数目的电子拉得更紧,给出更小的离子。
Watch the trend direction
- Atomic radius decreases across a period (more protons pull the same shell in) but increases down a group (extra shells).
- A cation is smaller than its atom; an anion is larger.
A common trap: radius decreases across a period even though electrons are being added — because the growing nuclear charge pulls the same shell inwards. Only adding a new shell (down a group) makes atoms bigger.
注意趋势方向
- 原子半径 沿一个周期 减小(更多质子把同一壳层拉进来),但沿一个族向下 增大(增加壳层)。
- 阳离子 比它的原子小;阴离子 比它的原子大。
一个常见陷阱: 半径沿一个周期减小,尽管电子在增加——因为增长的核电荷把 同一个 壳层向内拉。只有增加一个 新壳层(沿族向下)才会让原子变大。
You've got it
- across a period: radius decreases (more nuclear charge, similar shielding)
- down a group: radius increases (extra shells, more shielding)
- cation < atom; anion > atom
- among isoelectronic 等电子 ions, more protons → smaller
你掌握了
- 沿一个周期:半径 减小(更多核电荷,相近的屏蔽)
- 沿一个族向下:半径 增大(增加壳层,更多屏蔽)
- 阳离子 < 原子;阴离子 > 原子
- 在等电子离子中,质子越多 → 越小