Chemistry 2

1. 10

An Mg atom has 12 electrons.
An Mg atom loses 2 electrons to form an Mg^2+ ion.
No. of electrons in an Mg^2+ ion = 12 - 2 = 10


2. S2Cl2

S2Cl2 is a compound formed from two non-metals, and thus it is covalent.
Each of the other three compounds is formed from a metal and a non-metal, and thus they are ionic.


3. CO2, HCN, O2

CO2, HCN and O2 are substances formed from non-metals only, and thus they are covalent.
NaCl and NaClO4 are compounds formed from metals and non-metals, and thus they are covalent.
Although NH4Cl is a compounds formed from non-metals only, it is ionic. This is because NH4^+ ion behaves like metal ions.


4. I

Rn (not Ru) is a noble gas, and its electronegativity is very low (0).
In the Periodic Table, the electronegativity increases from left to right, and from top to bottom. The electronegativity of Si is lower than those of I and S. The electronegativity of a Group VII element is higher than that of a Group VI element other than oxygen, and thus I has a higher electronegativity than S.


5. NaCN

In NaCN, there is ionic bonds between Na^+ and CN^- ions. The CN^- ion is formed by a joining a C atom and an N atom by a triple covalent bonds, i.e. C≡N^-.


6. S^2-

Na^+ has the smallest radius because each Na^+ has only 2 shells, but each of other three ions has 3 shell.
All of Cl^-, Ca^2+ and S^2- are isoelectric with electronic configuration 2, 8, 8. The atomic numbers of Cl^-, Ca^2+ and S^2- are 17, 20 and 16 respectively. The nucleus of S^2- has the least number of protons to hold the 18 electrons, and thus it has the greatest radius (greatest size) among Cl^-, Ca^2+ and S^2-.


7. Si-F

The greater the difference in electronegativity between the two bonding atoms, the more polar the bond is.
Among Cl, C and Si, Si has the smallest electronegativity.
Between F and O, F has greater electronegativity.
Therefore, Si-F has the greatest difference in electronegativity between the two bonding atoms, and thus the bond is most polar.

Answer:
1.10, because magnesium ion needs to attain an octet structure for being stable,
so its electronic arrangement is (2,8) (i.e. losing 2 electrons)

2. S2Cl2. A covalent bond does not consist of metals generally.

3. CO2, HCN, O2

4.S, it can form an ion with charge 2-, while I only forms one with -.

5. ClF. It ionizes in water to form an ionic compound from its covalent structure.

6/7 Sorry I have no idea.