A:The electronic nature of chemical bonding

(a) The electronstatic forces between charged particles ​
Q: what is an electronstatic force?
The electrostatic forces is the force that cause attraction and repulsion between two charged particles.
According to the electronstatic force:

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- a positive charge particle and a negative charge particle attract ech other
- same charge particle repel each other
- as the distance of two particles are increasing, the attraction or the repulsion of two charged particles become smaller.
- if the charges on the two particles become larger, the attraction or repulsion of two particles become larger.
electstatic force explains the trends in pysical and chemical properties and it also explains the bonding between particles

(b) ELectron shellls
Q:what is an electron shell?
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www.chem4kids.com/ files/elem_pertable.html
each period on the periodic table is a different electron shell

eg: The first electron shell which is the first row of periodic table has 2electrons.
The second electron shell which is the second row of the periodic table has 8 electrons.

what is an atomic radius of an atom?
A: the atomic radius of an atom is the the distance from the nucles of the atom to the outter shell
What should happen to the atomic radius going from left to the right of the periodic table?
the atomic radius will become smaller since the atomic number of the elements increase as well as the positive and the negative charge. According to the electrostatic forces' rules, the larger the charge, the larger the attraction between two charged particles. As the attraction is increasing, the atomic radius is becoming smaller.
eg: The element Mg will have a larger atomic radius than Cl since Mg's atomic number is smaller, and the attraction between the nucleus and the electrons are smaller.
what shoud happen to the atomic radius going down a group?
the atomic radius becomes larger. As we going down a group of the peroidic table, the number of the electron shells increases since the atomic nunber of the atoms are increasing. Therefore, the atomic radius is becoming larger.
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www.periodictable.com/ Properties/A/AtomicRadi...
eg: Na will have a smaller atomic radius comparing to K because the element K will have more electron shells.
Q What is an open shell ?
It is a shell that can still contain more electrons
Q: What is a closed shell ?
It is the shell that cannot contain no more electrons
eg: The second electron shell which can hold maximum 8 electrons. The elements Be and N has the number of electrons less than 8 so their outermost shell is open. Ne has 8 electrons in the outermost shell so it's closed
(C) valence electrons

Q: What is the valence electrons?
they are electons in open shells.( Note that the "Valence" is used as an adj )
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(note that the valence electrons of the noble gas can either be "8" or "0" since the valence shells of the nobel gases are full )
eg: Oxygen has six calence electrons. Fluorine has seven valence electrons

(d) The valence of an atom( The valence of the transition metals is not considered in this section )
Q:how valence electrons are put into the the orbitals
--each orbital can hold maximun two electrons.
--each electron added is going to a new orbital becacuse electrons repel each other.
--after there are one electron in each orbital, the electron that is going to be added will go to the orbital that already contained one electron, and be paired.

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eg: Oxygen has six valence electrons. Carbon has four electrons.
Q: What is the valence of an atom? (we don't consider the transition metals)
The valence of an atom is the number of the unpaired electrons of an atom, and valence is sometimes called combining capacity. The "Valence" here is used as a noun.
For example:

Valence of an atom

The valence of oxygen is two. The valence of Carbon is four.

Exercise for the concepts:
1. which one has larger atomic radius, Cr or Zn? Explain your answer.
2. Which one has a larger atomic radius, Ca or Ra? Explain your answer.
3.which family of elements appears to possess only closed shells? (tex. P166#43)
4.How many electrons does Ca2+ has? Is the ion has an open shell or closed shell?
5. How many valence electrons does Mg have? What is the valence of Mg?
6.How many valence electrons does Cl have? What is the velence of Cl?

answers for the exercise:
1.Cr has a larger atomic answer comparing to Zn because Cr has a larger atomic number than Zn which means that the attraction between the nucleus and electrons is smaller. According to the rules of electrostatic forces, the smaller the attraction, the larger the distance.
2.Ra has a larger atomic radius because Ra has more electron shells comparing to Ca, therefore, it has a larger atomic radius.
3.The noble gases has closed shells because they all have eight electrons at their outermost shells.
4.Ca2+ loses 2 electrons comparing to Ca so it has eight electrons at the outermost shell, therefore, it has closed shell.
5.Mg has two valence electrons, and the valence of Mg is 2
6.Cl has seven valence electrons, and the valence of Cl is 1