Chemistry Chapter 8: Covalent Bonding

electronegativity difference and bond character

- 0-0.4 nonpolar covalent 0.4-1.7 polar covalent <1.7 ionic

exceptions to the octet rule

- a small group of molecules might have an odd number of valence electrons and be unable to form an octet around each atom. - few compounds form sub octets: stable configurations with fewer than eight electrons present around an atom - coordinate covalent bond: forms when one atom denotes both of the electrons to be shared with an atom or ion that needs two electrons to form a stable electron arrangement with lower potential energy. - central atoms that contain more than eight valence electrons.

electronegativity and bond character

- the type of bond formed during a reaction is related to each atoms attraction for electrons - the scale of electronegativity indicates the relative ability of an atom to attract electrons in a chemical bond

Covalent bond

A chemical bond that results from sharing valence electrons. - the shared electrons are considered to be part of the outer energy levels of both atoms involved - can occur between elements that are near each other on the periodic table, majority form between atoms of nonmetallic elements

double bonds

A double covalent bond forms when three pairs of electrons are shared between two atoms.

Resonance Structures

Resonance is a condition when more than one valid lewis structure can be written for a molecule or ion. The two or more correct Lewis structures that represent a single molecule or ion are referred to as resonance structures. - they differ only in the position of electron pairs, never the atoms positions. - the location of lone pairs and bonding pairs (single, double, triple) differ in these structures. -Each molecule or ion that exhibits resonance behaves as if it has only one structure.

pi bonds

a multiple covalent bond consists of one sigma bond and at least one pi bond. - pi bond: forms when parallel orbitals overlap and share electrons the shared electron pair of pi bond occupies the space above and below the line that represents where the two atoms are joined together.

hybridization

a process in which atomic orbitals mix and form new identical hybrid orbitals

Bond breaks

an energy change occurs when a bond between atoms in a molecule forms or breaks/ energy is released when a bond forms but energy must be added to break a bond.

Covalent bond formation

as two atoms approach each other several forces act. Two repulsive forces act on the atoms, one from each atoms like charged electron and one from each atoms like charged protons. As the atoms move closer the attraction of the protons in each nucleus for the other atom;s electrons increase until a point of maximum net attraction is achieved. at that point the two atoms bond covalently and a molecule forms. if the two nuclei move closer the repulsive forces increase and exceed the attractive forces. - most stable arrangement of atoms in a covalent bond exists at some optimal distance between nuclei. at this point the net attraction is greater than the net repulsion. unbonded pairs are known as lone pairs

ionic bonds

between metal and non metal covalent: between two non metals

Naming Binary Molecular Compounds

composed of two nonmetal atoms - the first element uses its entire name - the second element is named using its root and adding the suffix (ide). - prefixes are used to indicate the number of atoms of each element that are present in the compound.

bond character

depends on how strongly each of the bonded atoms attracts electrons.

intermolecular forces

differences in properties are a result in attractive forces. in a covalent compound the covalent bonds between atoms in molecules are strong but the attraction forces are weak. the weak attraction forces are known as intermolecular forces.

polar covalent

form because not all atoms that share electrons attract them equally when a polar covalent bond forms the shared electron pair or pairs are pulled toward one of the atoms thus the electrons spend more time around that atom than the other atom

Triple atoms

forms when three pairs of electrons are shared between two atoms.

electron affinity

measure of the tendency of an atom to accept an electron. - increases with increasing atomic number within a period and decreases with increasing atomic number within group - electronegativity values were assigned whereas electron affinity values were measured

VSEPR model

model based on an arrangement that minimizes the repulsion of shared and unshared electron pairs around the central atom

diatomic molecules

molecules like H2 N2 and O2 are called hydrogen molecule, nitrogen molecule and oxygen molecule

Lewis dot structures

represents the arrangement of electrons in a molecule. - a line or pair of vertical dots between the symbols of elements represents a single covalent bond.

Sigma bonds

single covalent bonds that occur when the pair of shared electrons is in an area centered between the two atoms. When two atoms share electrons their valence atomic orbitals overlap end- to- end concentrating the electrons in a bonding orbital between the two atoms. They can form when s orbital overlaps with another s orbital or a p orbital, or two p orbitals overlap end-to-end.

bond dissociation energy

the amount of energy required to break a specific covalent bond, always a positive value. - also indicates the strength of a chemical bond because of the inverse relationship between bond energy and bond length. the smaller bond length the greater the bond dissociation energy is.

bond length

the strength of a covalent bond depends on the distance between the bonded nuclei. distance between two bonded nuclei is called the bond length. determined by the sizes of the two bonding atoms and how many electron pairs they share. the shorter the bond length the stronger the bond.

trigonal planar

the three bonding electron pairs have maximum separation

linear pair

when bonding electrons have maximum separation. two pairs of electrons shared with the central atom

trigonal pyramidal

when it has three single covalent bonds and one lone pair.

bent

when it has two covalent bonds and two lone pairs

tetrahedral

when the central atom has four pairs of bonding electrons.

hybrid orbitals

when two things are combined and the result has characteristics of both