Unit #4: Covalent Bonding
What is a lone pair?
A pair of electrons that are not bonding together so they are both on the same element. (Drawn as dots :)
What is a bonding pair?
A pair of valence electrons, one from each element that are "shared" to create a covalent bond. (Drawn as a dash -----).
What is a molecular formula and what information does it contain?
A representation of a compound that contains the elements (written as letters) and their ratios (written as numbers: substripts).
How are polar bonds formed?
Because of the unequal sharing of electrons in a covalent bond. One element pulls the shared electrons closer to itself causing it to be slightly negative.
Compare and contrast ionic bonds with covalent bonds.
Both types join different elements to create a compound and achieve a noble gas configuration. But ionic compounds TRANSFER electrons while covalent compounds share electrons
How is a covalent bond formed?
By the sharing of valence electrons. The attraction of these electrons to the positive charge in the nucleus holds the bond together.
What is a binary compound? Give an example of a binary molecular compound. Give an example of a Binary Ionic Compound.
Consists of only two different elements. Binary ionic= NaCl Binary molecular compound= H2O
What is the difference between an ionic compound and a molecular compound?
Ionic compounds contain a metal and a nonmetal. A molecular compound contains only nonmetals.
Determining bond type using electronegativity
Less than 0.3 = Non-polar covalent 0.3-1.7 = Polar covalent Over 1.7 = Ionic
Steps for Drawing Lewis Structures
1 . Determine the type and number of the atoms in the molecule. 2. Count up all of the valence electrons and write the total. 3. Usually the lowest electronegativity element is placed in the center. The remaining atoms are placed around the center, spaced evenly. 4. Connect the central atom to the each of the remaining atoms with single bonds. 5. Count how many valence electrons you have used so far and how many remained. 6. Distribute valence electrons to the "outer" atoms until they have a stable octet. 7. Place any remaining electrons onto the central atom. 8. Lastly, each atom needs to have a stable octet. You can move electrons from one atom to another. Make double bonds or triple bonds if required.
What is a diatomic molecule? What are the seven common diatomics?
A molecule that exists as two of the same elements bonded together: H2 N2 O2 F2 Cl2 Br2
What is a polar bond?
A bond with a separation of charge causing one end of the bond to be slightly positive, and the other end to be slightly negative.
What is a covalent bond?
A chemical bond between two nonmetals.
Molecular geometry is the part of chemistry that deals with the _______ of molecules.
Shape
Why is knowing about the shape of a molecule important?
Shape determines many properties about a molecule such as reactivity, smell, taste, etc.
What is the periodic trend in electronegativity? Meaning how does electronegativity change as we move up/down on the periodic table? AND meaning how does electronegativity change as we move left/right on the periodic table?
The electronegativity increases as we move from left to right. It incerases as we go from the bottom, to the top of the table.
Why is a covalent bond formed?
The elements can all acheive a noble gas electron configuration. Eight is great! Except hydrogen which only needs two valence electrons.
What is a molecule?
The smallest representative unit of a covalently bonded substance.
What is electronegativity?
The tendency of an element to attract electrons to itself in a bond. Fluorine is the highest, Francium is the lowest.
Why do atoms in molecules want to spread out as far as possible?
To reduce the "like charge repulsion" between their outer electrons.
VSEPR Theory
Valence Shell Electron Pair Repulsion; molecules will take on shape that is lowest in energy. A low energy shape is the one that minimizes the VSEPR between two adjacent atoms.