Covalent Bonding and Molecular Structure

Bond Length
The optimum distance between nuclei where the net attractive forces are maximized.
Structural Formula
A formula for a molecule that shows specific bonds between atoms.
Chemical Formula
Molecular formula. Gives the number and type of each element in the molecule.
Bond Dissociation Energy
The amount of energy that must be supplied when a bond breaks or the amount of energy released when a bond is formed.
Electronegativity
The ability of an atom to attract shared electrons in a covalent bond. Increases from left to right along a period of the periodic table. Increases from bottom to top of a group on the periodic table.
Electron-Dot Structure
Lewis Structure. A structure that represents an atom’s valence electrons by dots and indicates by the placement of dots how the valence electrons are distributed in a molecule.
Lone Pair
Nonbonding pair; A pair of valence electrons assigned to an atom in a Lewis structure that are not involved in bonding.
Bonding Pair
Shared valence electrons in a dot structure that make up bonds between atoms
Formal Charge
The number of valence electrons for a free atom minus the number of valence electrons assigned to a bonded atom.
Polar Covalent Bond
A covalent bond in which the bonding electrons are shared unequally.
Nonpolar Covalent Bond
A covalent bond in which the bonding electrons are shared equally.
Valence-Shell Electron-Repulsion (VSEPR) Model
A model for predicting the approximate shape of a molecule.
Charge Cloud
A cloud of electrons assigned to an atom in a molecule and used to determine the approximate shape of the molecule. A single charge cloud could be one lone pair, one single bond, one double bond, or one triple bond.
Bond Angle
The angle at which two adjacent bonds intersect.
Valence Bond Theory
A theory that visualizes the orbital picture of how electron pairs are shared in a covalent bond.
Sigma Bond
A bond that forms from the head-on overlap of atomic orbitals. Always the first bond to form between two atoms in a molecule.
Pi Bond
A bond that forms from the parallel overlap of two p orbitals. Only present in double (1 pi) or triple bonds (2 pi).
sp2 hybridized orbital
An atomic orbital formed by the hybridization of an s orbital with two p orbitals.
sp hybridized orbital
An atomic orbital formed by the hybridization of an s orbital with one p orbitals.
sp3 hybridized orbital
An atomic orbital formed by the hybridization of an s orbital with three p orbitals.
Molecular Orbital
A wave function whose square gives the probability of finding an electron within a given region of space in a molecule.
Atomic Orbital
A wave function whose square gives the probability of finding an electron within a given region of space in an atom.
Molecular Orbital (MO) Theory
A quantum mechanical description of bonding in which electrons occupy molecular orbitals that below to the entire molecule rather than to an individual atom.
Bonding Molecular Orbital
A molecular orbital that is lower in energy than the atomic orbitals from which it is derived.
Anti-Bonding Molecular Orbital
A molecular orbital that is higher in energy than the atomic orbitals from which it is derived.
Bond Order
The number of electron pairs between atoms. (# of bonding electrons – # of antibonding electrons) divided by two.
Formal Charge Equation
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Alkali Metals
Group 1A elements. Rapidly react with water to form alkaline products. Soft, silvery metals. Never found in a pure state in nature.
Alkaline Earth Metals
Group 2A elements. Lustrous, silvery metals. Less reactive than the Group 1A elements. Never found in a pure state in nature.
Halogens
Group 7A elements. Found in nature only in combination with other elements, such as salts.
Noble Gases
Group 8A elements. Colorless gases with very low or no chemical reactivity.
Calorie
1000 calories or 1 kilocalorie or 4.184 kJ
calorie
a unit of energy measured as the amount of energy required to increase the temperature of 1 g of water by 1 degree Celcius
Joule
SI unit of energy
Rule #3 for Rounding
If the first digit you remove is a 5 and there are nonzero digits following, round up.
Rule #4 for Rounding
If the first digit you remove is a 5 with nothing or a 0 following, round down.

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