Covalent and Metallic Bonding
Dr. Melinda Oliver
Physical Science II
Understanding the Differences Between Ionic and Covalent Compounds
https://www.youtube.com/watch?v=PKA4CZwbZWU
Naming the two classes of compounds (ionic and covalent) is different but the same too!
When the compound contains a metal, that is a pretty big clue that the compound is ionic and you will name it as described on the previous smore. If the compound contains two nonmetals, then you will use the prefixes as outlined below. Formulas and naming are super easy for covalent compounds, just use the prefixes to indicate how many of each element are present in the formula.
Naming Binary Covalent Compounds
You can use the prefixes now! (Binary = two elements) We can call most covalently bonded substances Molecular! This is not true for ionic compounds (no true molecules)
- Nonmetal to the left on PT comes first in formula and in name. Do not change name. You will see exceptions to this "rule" especially for hydrogen.
- Use the subscripts in the formula to determine the prefixes. The figure to the right has the prefixes from 1-10. Most of these are familiar.
- If the element to the left on the PT, and, hence, in the formula, has no subscript, which means there is only one of this element in the formula, the prefix mono- is not used.
- The other nonmetal comes second in formula and in name. Drop the ending on this one and add the suffix -ide. So pretty much the same as ionic compounds.
- Do not try to figure out charges as these elements are sharing.
- Example: CO2 is carbon dioxide. Carbon is on the left and there is only one C in the formula (so no mono- prefix). N2O4 is dinitrogen tetroxide. We do not usually put two vowels next to ech other so that is why it is not tetraoxide.
https://www.youtube.com/watch?v=DejkvR4pvRw
Speaking of nonmetals...
Nonmetals are the only elements that can exist as molecules.
Not all elements exist as just one atom but most do. The exceptions are outlined below.
As we move into chemical changes, it is important to know what the formulas are for elements too. For most, it is just the symbol for that element because those elements are "atomic". Examples are any element except for the ones below!
Molecular Elements-diatomic
As an important part of the language of chemistry, knowing which elements are atomic (all of them except for the 7 identified here along with P and S) and which are molecular is especially necessary when we get to writing chemical reactions, etc. When we draw Lewis dot structures for these elements, the molecule must be used.
Phosphorus is another molecular element
There are many forms of phosphorus (white, red, black, etc). Most of the time, the formula is specified but this is another molecular element.
Sulfur is another molecular element
Technically, sulfur is S8 (subscript 8) in in its elemental form.
Lewis dot symbols for elements depicts number of valence electrons.
Lewis dot symbols for molecules show how the atoms in a molecule are arranged.
Some covalent compounds are "ionic like": polar vs nonpolar
The two classes of compounds (ionic and covalent) are not separated by a wall! It is more like a tug-of-war contest (see dog video on last smore!) where there is equal tugging on electrons (tugging in the atomic world = electronegativity) to the other end where one atom loses and one atom gains. So at the equal tugging end you end up with completely nonpolar covalent compounds (no charges, equal sharing between two atoms) and on the other end we have ionic compounds where there is no sharing (metal loses electrons and nonmetal gains electrons) which we discussed on our last smore. In between the two are covalent compounds that have bonds where the tug-of-war because more and more unequal and you may or may not end up with a polar compound. We can make some assumptions about polarity based on the polarity of bonds and how symmetrical a molecule is. You can SEE the effects of this unequal sharing in the properties like melting, conductivity, and solubility.
Polar & Non-Polar Molecules: Crash Course Chemistry #23
Electronegativity DIFFERENCE tells us whether a bond is polar or nonpolar.
In the top example we an H-H bond. The electronegativity DIFFERENCE is 2.1-2.1 (see table below for electronegativities) = 0 so this is a completely nonpolar bond.
The second example, HF, has an electronegativity DIFFERENCE of 1.9 which is pretty much ionic! Use the same guide as the electronegativity paper lab for this week.
Electronegativity Difference Guide
The ranges below do not match all textbooks but these are the ranges used by the paper lab on electronegativity paper lab.
Electronegativity DIFFERENCE: 0-0.5 --> nonpolar; 0.6-1.7 --> polar; > 1.7 --> ionic
Metals are different!!
https://www.youtube.com/watch?v=VtRP6RDwQIg
https://www.youtube.com/watch?v=0A_4QgEbTww
What can you do to help your understanding?
Chemistry is a subject that must be practiced everyday if possible. Work through the lecture examples stopping the video clips and then restarting to check yourself. Take advantage of the practice outlined above AND the questions in Mastering Physics to give you the practice you need to be successful. DO NOT PROCRASTINATE! Email me with questions!!
Have Questions Later?
Dr. Melinda Oliver
Physical Science II Instructor
Bishop State Community College
Email: moliver@bishop.edu
Location: Mobile, AL, United States
Phone: (251)405-4504