Unit 2: Topic 1 - Types of Chemical Bonds Flashcards
What is electronegativity and its trend on the periodic table?
Electronegativity measures an atom’s tendency to attract and form bonds with electrons. Electronegativity increases from left to right across periods and bottom to top across groups.
Flourine has the greatest electronegativity because it has 7 valence electrons (1 away from completing its valence shell), least electron shielding, and greatest proton attraction in its period.
Noble gases have no electronegativity because they already have a stable electron configuration (8 valence electrons).
What is the octet rule?
The octet rule refers to the tendency of atoms to achieve 8 electrons in their most outer shell (valence electrons) through bonds. Atoms with less than 8 valence electrons tend to form bonds and become more stable.
How does the octet rule affect electronegativity?
Electronegativity increases from left to right because elements to the left of the periodic table have fewer valence electrons and “give up” their electrons more easily to form an octet. Elements to the right of the periodic table have more valence electrons and have a higher attraction for electrons to form an octet.
Noble gases have no electronegativity and rarely form bonds because they already have a stable electron configuration.
Exceptions to the octet rule
Exceptions to the octet rule include but are not limited to:
- Hydrogen and Helium outer shells have a maximum of 2 electrons.
- Transition metals can have 18 valence electrons.
- Instances of lack or abundance of electrons (odd # of electrons (common in compounds with boron), incomplete octet (e.g. BCl3), expanded octet (e.g. PCl5)).
What is Coulomb’s law?
Coulomb’s Law describes the attraction and repulsion between two particles and is defined by F=(kq₁q₂)/r²
F: attractive force
k: Coulomb’s constant (about 8.98755 × 10⁹ kg⋅m³⋅s⁻⁴⋅A⁻²)
q₁, q₂: charges of the two particles
r: the distance between the particles
How does Coulumb’s law affect electronegativity?
Coulomb’s Law can be applied to the attraction between the nucleus and electrons of atoms:
- Electronegativity increases from left to right: Attractive force increases. As you go across a period, the number of protons increases (charge increases). A greater charge results in a stronger attraction and electrons are more difficult to remove (F increases because q₁q₂ increases). Atoms will be more inclined to take in electrons than give them away.
- Electronegativity decreases from top to bottom: Attractive force decreases. As you go down a group, more shells and electrons are added. These electrons are farther from the nucleus and are, therefore, less attracted to the nucleus and easier to remove (F decreases because r² increases).
What type of bond is created between two atoms with similar electronegativity? Why?
A nonpolar covalent bond is created between two atoms with similar electronegativity because their attractive forces are extremely similar that the electrons are shared equally between the two and so there is no difference in charge (nonpolar). The common bond between two nonmetals.
The general rule is that a difference in electronegativity of less than 0.4 is considered nonpolar (but this boundary is not definite as electronegativity is a spectrum, e.g. H-C is a nonpolar bond despite carbon having a slightly greater electronegativity than hydrogen).
What type of bond can be created between two atoms with slightly unequal electronegativity? Why?
A polar covalent bond is created between two atoms with slightly unequal electronegativity. The difference in their attractive forces causes the bonded electrons to be closer to one atom than the other, resulting in a slightly negative charge on the more electronegative atom and a slightly positive charge on the less electronegative atom. The common bond between a nonmetal and a nonmetal or metalloid.
The general rule is that a 0.4-2.0 difference in electronegativity constitutes a polar covalent bond
What type of bond can be created between two atoms with greater unequal electronegativity? Why?
When the difference in electronegativity is high enough, an ionic bond is created because the electron is transferred from one atom to another, creating an anion and a cation, and the bond is held together by the atoms’ attraction to each other.
The general rule is that a metal to non-metal atom bond constitutes an ionic bond.
In single bonds, how do differences in electronegativity affect bond dipoles?
Greater differences in electronegativity lead to greater bond dipoles because the stronger attractive forces cause electrons to be closer to the more electronegative atom. The closer the shared electrons are to an atom, the more negative the charge is and the greater the bond dipole is. As bond dipoles increase, the bond type changes from nonpolar covalent to polar covalent and to ionic when the electrons close enough to the more electronegative atom that the electrons are transferred between the atoms instead of shared.
To what extent can ionic and polar covalent bonds be distinguishable by electronegativity?
Ionic and polar covalent bonds can be somewhat distinguishable if the difference in electronegativity is significant enough. However, all polar bonds have some ionic character because the electrons are closer to the more electronegative atom, creating a diplole.
Bond polarity and difference in electronegativity is a spectrum with approximate values for each bond type. Generally, 0.4-2.0 is polar covanlent, and 2.0+ is ionic, but this varies between sources.
Therefore, bond types are more accurately represented by the types of atoms bonded (nonmetal-nonmetal/metalloid: covalent, metal-nonmental: ionic)
How can types of atoms (nonmetal, metalloid, metal) be used to characterize bonding?
Aside from using electronegativity, we can characterize bonds by the properties of atoms that are bonded:
- Covalent: nonmetal and nonmetal (use electronegativity to determine if the bond is likely nonpolar or polar)
- Ionic: nonmetal and metal
- Metallic: metal and metal
What are delocalized electrons?
Delocalized electrons are electrons in a molecule, atom, or metal that are not associated with any individual atom. They are found in metallic solids (metal-and-metal bonded compounds) and give metals their numerous properties (conductivity, heat capacity, malleability, ductility, etc.). The metal is held together by the attraction between the positive and negative forces.
In a metallic solid, valence electrons are delocalized and are free to move within the metal. This is depicted in the electron sea model. A greater number of delocalized electrons result in a stronger metallic bond.
