查看完整版本: some f3 chem questions

some f3 chem questions

1. How can I know the ion charge of transition metal? I can handle those first 20 elements well, but not for transition metal, like zinc ion, why its ion is Zn2+, but not 6+? Isn't its nearest noble gas is krypton?

2. 'A molecule is the smallest part of an element or a compound which can exist on its own under ordinary conditions.' Why non-metal elements cannot exist on its own, but need to form a molecule?

3. Some covalent compounds are composed of discrete molecules, their atoms within a molecule are strongly
bonded together by covalent bonds and have a sinmple molecular structures, while  a few elements and compounds, non-metal atoms are joinedby covalent bonds to form a giant network, how can I find out whether a covalent substance is simple molecular structire or giant covalent structure?


thank you

回覆 #1 dilloncyh 的帖子

1. You need to study the atomic structure and electronic configuration in senior form and learn the concept of "orbital". Then you can get a brief explanation for your question.

2. It is mainly due to the problem of stability. For example, why F exists as F2 under ordinary condition? It is due to the extra stability of the octet structure. After you have learnt more, you will understand more.

3. In secondary school studies, you only need to memorize a few examples of giant covalent structure like diamond, quartz, etc. You just need to treat other covalent compounds as simple molecular structure is okay.

so I just remember the names and formulae of the substances hat I come across in testbook/exercise book then ok?

回覆 #3 dilloncyh 的帖子

For giant covalent structure, just memorize those examples in textbooks, exercise books are okay.
Also, you may pay attention on the difference in physical properties (e.g. boiling point, etc.) between simple molecular and giant covalent structure.

我們可依從物質的性質推測物質的結構,
                       
PREDICTING THE STRUCTURE OF A SUBSTANCE
FROM ITS PHYSICAL PROPERTIES

Physical properties 物質的結構             Structure 物理的性質                                               

a gas or liquid at room conditions          simple molecular structure
low melting point/boiling point
在常溫常壓下是氣體或液體                簡單分子結構
固體的熔點頗低
         
very high melting point                         Giant covalent structure
熔點非常高                                 巨型共價結構