Chapter 8: Bonding: General Concepts Flashcards
Bond energy
Energy required to break the bond
Ionic bonding
The electrostatic attraction between oppositely charged ions
Why are bonds formed?
So the system can achieve the lowest possible energy by behaving this way
Ionic compound
A compound that results when a metal reacts with a nonmetal to form a cation and an anion (any compound that conducts an electric current when melted)
Coulomb’s law
E = (2.31 x 10^-19 J • nm)(Q1Q2/r)
E = energy of interaction between a pair of ions
r = distance between the ion centers in nm
Q1 and Q2 = numerical ion charges
Bond length
The distance between the nuclei of the two atoms connected by a bond; the distance where the total energy of a diatomic molecule is minimal
Covalent bonding
A type of bonding in which electrons are shared by atoms
Polar covalent bond
A covalent bond in which the electrons are not shared equally because one atom attracts them more strongly than the other
Electronegativity
The ability of an atom in a molecule to attract shared electrons to itself
On the periodic table, electronegativity increases…
Going left to right across a period
On the periodic table, electronegativity decreases…
Going down a group for representative elements
Dipole moment
A property of a molecule whose charge distribution can be represented by a center of positive charge and a center of negative charge
Types of molecules with polar bonds but no resulting dipole moment
- Linear molecules with two identical bonds
- Planar molecules with three identical bonds 120 degrees apart
- Tetrahedral molecules with four identical bonds 109.5 degrees apart
When a positive ion is formed by removing one or more electrons from a neutral atom, the resulting cation is _____ than its parent atom.
Smaller
When a negative ion is formed by add one or more electrons to a neutral atom, the resulting anion is _____ than its parent atom.
Larger
On the periodic table, ion sizes increase…
Down a group
Isoelectric ions
Ions containing the same number of electrons
Lattice energy
The change in energy that takes place when separated gaseous ions are packed together to form an ionic solid
[k(Q1Q2)]/r
Lattice energy processes become more exothermic when…
Ionic charges increase and distances between the ions in the solid decrease
Percent ionic character of a bond
(measured dipole moment of X-Y/calculated dipole moment of X+Y-) x 100%
Single bond
A bond in which one pair of electrons is shared by two atoms
Double bond
A bond in which two pairs of electrons are shared by two atoms
Triple bond
A bond in which three pairs of electrons are shared by two atoms
For bonds to be broken, energy must be ______ to the system
Added
The formation of a bond ________ energy
Releases
∆H
∆H = ∑n x D(bonds broken) - ∑n x D(bonds formed)
Localized electron model
A model that assumes that a molecule is composed of atoms that are bound together by sharing pairs of electrons using the atomic orbitals of the bound atoms
Lone pair
An electron pair that is localized on a given atom; an electron pair not involved in bonding
Bonding pair
An electron pair found in the space between two atoms
Lewis structure
A diagram of a molecule showing how the valence electrons are arranged among the atoms in the molecule
Duet rule
Hydrogen forms stable molecules when it shares two electrons
Octet rule
The observation that atoms of nonmetals tend to form the most stable molecules when they are surrounded by eight electrons (to fill their valence orbitals)
Steps for writing Lewis structures
- Find the total number of valence electrons. Add an electron for every negative charge. Subtract an electron for every positive charge.
- Decide the central atom (least electronegative, except for H) and draw bonds. Subtract the electrons used from the total in step 1.
- Assign the leftover electrons to the terminal atoms. Subtract the electrons from the total in step 2.
- If necessary, assign any leftover electrons to the central atom. If the central atom has an octet or exceeds an octet, you are usually done. If central does not have an octet, create multiple bonds.
Which elements should always be assumed to obey the octet rule?
C, N, O, and F
Which elements often have fewer than eight electrons around them in their compounds?
B and Be
Which elements never exceed the octet rule?
Second row elements because their valence orbitals can only hold 8 electrons.
Which elements can exceed the octet rule?
Third row and heavier elements because of their empty d orbitals
Resonance
A condition when more than one valid Lewis structure can be written for a particular molecule. The actual electronic structure is not represented by any one of the Lewis structures but by the average of all of them
Formal charge
The difference between the number of valence electrons on the free atom and the number of valence electrons assigned to the atom in the molecule
(number of valence electrons on free atom) - (number of valence electrons assigned to the atom in the molecule)
Assigned valence electrons = (number of lone pair electrons) + 1/2(number of shared electrons)
Molecular structure
The three-dimensional arrangement of the atoms in a molecule
