S.2.2 Flashcards
What is the covalent model used for?
To predict how bonds will be formed based on Lewis’ formula
What does the VSEPR model stand for?
Valence Shell Electron Pair Repulsion model
What is the result of covalent bonds forming?
Energy is at a minimum
What rule do atoms tend to follow when bonding?
Octet rule
What are exceptions to the octet rule?
Small atoms and incomplete octets
How do you calculate the number of electrons for Lewis’ formula?
Multiply the number of valence electrons of each element by the number of atoms of that element in the formula
What is the first step in identifying the electron structure in Lewis’ formula?
Draw crosses and dots, or dashes between the central atom and each of the outer electrons
What types of bonds can be formed?
Single bonds, double bonds, triple bonds
What happens to bond length and strength as you move down the atomic radius?
Bond length increases, bond enthalpy decreases
What is a Lewis acid/base?
Species that accept or donate a pair of electrons
What defines the shape of a molecule?
Repulsion between electron domains around a central atom
How do you account for charges when calculating valence electrons?
Add electrons for negative charge, subtract electrons for positive charge
What is the bond angle for 2 electron domains?
180° (linear)
What is the bond angle for 3 electron domains?
120°
What is the bond angle for 4 electron domains?
109.5° (tetrahedral)
What happens to bond angles in the presence of double bonds?
They might be slightly distorted due to increased repulsion
What is coordination bonding?
Both shared electrons come from the same atom
What does a transition element do when it forms a bond?
It can coordinate with one or more molecules or ions via coordinate covalence
What is the relationship between bond strength and bond type?
Short bonds are stronger than long bonds
Fill in the blank: Covalent bonds form when energy is at a _______.
minimum
What increases the repulsion in H2O?
The presence of 2 lone pairs increases the repulsion.
Angle is reduced between molecules.
What are London dispersion forces?
Forces arising from polar bonds due to unequal sharing of electrons.
What is electronegativity?
A measure of the ability of an atom to attract electrons in a covalent bond.
Electronegativity increases as effective nuclear charge increases and atomic radius decreases.
What happens to electronegativity in atoms with nearly empty shells?
They are less electronegative.
What are temporary dipoles?
Temporary dipoles occur when electron density becomes unevenly distributed due to constant movement of electrons.
What are induced dipoles?
Induced dipoles influence nearby atoms or molecules, creating temporary attractions.
How does electronegativity change across a period?
Electronegativity increases across a period.
How does electronegativity change up a group?
Electronegativity decreases up a group.
What is a pure covalent bond?
A bond between the same atoms covalently bonded.
Example: F2, O2, H2 have a difference in electronegativity = 0.
What characterizes a polar covalent bond?
Unequal sharing of electrons.
What characterizes an ionic bond?
Complete transfer of electrons.
What is dipole-dipole attraction?
Attraction between molecules that have permanent dipoles.
What is dipole-induced dipole attraction?
Attraction caused by a temporary separation of charge.
What is required for a molecule to be IR active?
It must contain an overall dipole.
What is hydrogen bonding?
Occurs when a molecule contains hydrogen covalently bonded to a very electronegative atom.
What are crystals?
Single molecules with a regular repeating pattern of covalent bonds.
What are allotropes?
Different bonding and structural patterns of the same element in the same physical state.
How do covalent compounds compare to ionic compounds in terms of boiling points?
Covalent compounds have lower boiling points than ionic compounds.
What types of bonds are present in hydrogen bonding?
Contain H-O, H-N, H-F.
What is the relationship between polar and non-polar molecules?
They can mix, resulting in a mixture of polar and non-polar characteristics.
