Atoms and bonding · 原子与化学键
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| atom/ˈætəm/ | 原子 | yuán zi |
| atomic number/əˈtɒmɪk ˈnʌmbə/ | 原子序数 | yuán zi xù shù |
| mass number/mæs ˈnʌmbə/ | 质量数 | zhì liàng shù |
| isotopes/ˈaɪsətəʊps/ | 同位素 | tóng wèi sù |
| periodic table/ˌpɪərɪˈɒdɪk ˈteɪbl/ | 元素周期表 | yuán sù zhōu qī biǎo |
| ionic bonds/aɪˈɒnɪk bɒndz/ | 离子键 | lí zi jiàn |
| covalent bonds/ˈkəʊvələnt bɒndz/ | 共价键 | gòng jià jiàn |
An ion changes electrons, not element identity
- Neutral sodium-23 has 11 protons, 12 neutrons and 11 electrons. After it loses one electron, Na⁺ has 10 electrons but still has 11 protons and remains sodium.
- An atom 原子 contains a nucleus and electrons in the introductory model. Atomic number 原子序数 counts protons; mass number 质量数 counts protons plus neutrons.
What determines which element an atom is?
The atomic number is the element. Change the neutrons and you have an isotope of the same element.
Find neutrons from the two numbers
- Neutron number follows $N=A-Z$. For sodium-23, $N=23-11=12$; for sodium-24, $N=24-11=13$.
- Isotopes 同位素 share proton number and differ in neutrons. Hydrogen-1 has one proton and no neutrons, so “every nucleus contains neutrons” is false.
Sodium-24 has atomic number 11. How many neutrons does it contain?
N = A - Z = 24 - 11 = 13.
Connect table position to bounded patterns
- The periodic table 元素周期表 orders elements by atomic number. Introductory main-group patterns connect similar outer-electron arrangements with similarities in chemical behaviour.
- A group does not make all its elements identical. Use the model at its stated level rather than extending a simple outer-electron rule to every element and property.
In an introductory main-group model, what helps explain similarities within periodic-table groups?
Outer arrangements help explain main-group patterns. They do not make group elements identical or replace more detailed models for every element.
Distinguish ion formation from the ionic bond
- Electron transfer can explain ion formation. Ionic bonds 离子键 are electrostatic attractions between opposite ion charges; the transfer itself is not the attraction.
- In the sodium/chlorine model, Na⁺ has 11 protons and 10 electrons, while Cl⁻ has 17 protons and 18 electrons. Opposite charges attract; bulk sodium chloride forms an ionic structure, not separate NaCl molecules in this model.
Match each bonding model to its defining feature.
Electron transfer can explain formation of ions; the ionic bond is their electrostatic attraction. Covalent models use shared pairs.
In the supplied model, Na⁺ retains 11 protons after neutral sodium loses one electron. How many electrons remain?
Neutral sodium has 11; losing one leaves 10.
Use a different model for shared electron pairs
- Covalent bonds 共价键 involve shared electron pairs. For a simple H₂ molecule, the bond is described by a pair of electrons shared between the hydrogen atoms.
- A compound's properties depend on structure and bonding, not just a list of constituent elements. Do not infer that a compound must behave like the separate elements or must be unreactive.
Atoms do not “want” electrons. Explain particle counts, electrostatic attraction and the appropriate bonding model; follow approved procedures for any real chemical work.
A compound must have the same properties as its separate constituent elements.
Structure and bonding matter. Do not infer identical properties from the constituents or describe compounds as universally unreactive.
Check all three particle counts
- Changing neutrons gives a different isotope of the same element; changing electrons gives a different charge state. Changing proton number changes element identity.
- For each supplied example, write protons, neutrons and electrons before naming its isotope or charge. A positive charge means fewer electrons than protons, not necessarily extra protons.
Use $Z=\text{protons}$, $A=\text{protons}+\text{neutrons}$ and charge balance separately. Keep ion formation, ionic attraction and covalent sharing distinct.
Explain why Na⁺ has ten electrons but is still sodium in the supplied particle model.
Example: “Losing one electron leaves ten, but the unchanged eleven protons still identify sodium.”
Losing an electron changes sodium into a different element.
False: unchanged proton number keeps the element identity.