Why are they ionic or covalent?
• N2 • CCl4 • SiO2 • AlCl 3 • CaCl2 • LiBr
I will be happy to critique your thinking. Include molecule symmetry in your thinking.
Whether they are ionic or covalent (or polar covalent) depends upon the difference in electronegativity (EN) of the two elements. Look up the EN of each element from tables in your text or some other source. . Different instructors and different texts use slightly different breakdowns but I use a difference of about 1.7 to indicate a 50-50 bond.
non-polar covalent: 0.0-0.4
polar covalent: 0.5-1.6
ionic: 1.7 and up (Can be as high as 2.1 and up in some textbooks.)
For example, H has an EN of 2.1 so the difference between two is zero. That is a covalent bond since each H attracts the two electrons shared equally. For LiF, Li is about 1 and F is 4.0. The difference is 3 so that is an ionic bond and it shows the F attracts the shared pair to the point that a Li electrons is essentially moved completely to fill the F atom to form the F ion. In between is something like SiO2. Si is about 2 and O is about 3.5. The difference is about 1.5 so this is polar covalent.
To determine whether a compound is ionic or covalent, we need to consider the elements involved and their electronegativity values.
1. N2 - Nitrogen (N) is a nonmetal and has a similar electronegativity value. Therefore, it forms a covalent bond, as both atoms equally share a pair of electrons.
2. CCl4 - Carbon (C) and chlorine (Cl) have significantly different electronegativity values. Chlorine is much more electronegative than carbon, so it will attract the shared electrons more strongly. As a result, the carbon-chlorine bonds will be polar covalent. However, due to the symmetrical arrangement of the four chlorine atoms around the central carbon atom, the individual bond polarities cancel out, making the overall molecule nonpolar covalent.
3. SiO2 - Silicon (Si) is a nonmetal, and oxygen (O) is also a nonmetal. Nonmetals usually form covalent bonds. Silicon forms four covalent bonds with the two oxygen atoms, resulting in a compound called silicon dioxide or silica.
4. AlCl3 - Aluminum (Al) is a metal, and chlorine (Cl) is a nonmetal. Metals and nonmetals typically form ionic compounds. Aluminum donates three electrons to each chlorine atom, resulting in the formation of three ionic bonds. Therefore, AlCl3 is an ionic compound.
5. CaCl2 - Calcium (Ca) is a metal, and chlorine (Cl) is a nonmetal. As mentioned before, metals and nonmetals typically form ionic compounds. Calcium donates two electrons to each chlorine atom, leading to the formation of two ionic bonds. Thus, CaCl2 is an ionic compound.
6. LiBr - Lithium (Li) is a metal, and bromine (Br) is a nonmetal. Again, metals and nonmetals generally form ionic compounds. Lithium donates one electron to the bromine atom, resulting in the formation of an ionic bond. Therefore, LiBr is an ionic compound.