Chemistry: Chapter 8 Flashcards
define covalent bond
a bond formed when electrons are shared between atoms
define molecule
a neutral group of atoms joined together by covalent bonds
define diatomic molecule
a molecule consisting of two atoms
define molecular compound
a compound that is composed of molecules
define molecular formula
a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound
define single covalent bond
a bond formed when two atoms share a pair of electrons
define structural formula
a chemical formula that shows the arrangement of atoms in a molecule or a polyatomic ion
each dash b/t a pair of atoms indicates a pair of shared electrons
define unshared pair
a pair of valence electrons that Is not shared between atoms
define double covalent bond
a bond in which two atoms share two pairs of electrons
define triple covalent bond
a covalent bond in which three pairs of electrons are shared by two atoms
define coordinate covalent bond
a covalent bond in which one atom contributes both bonding electrons
define polyatomic ion
a tightly bound group of atoms that behaves as a unit and has a positive or negative charge
ex. NH4^+ or SO3^2-
define bond dissociation energy
the energy required to break the bond b/t two covalently bonded atoms
usually expressed in kJ per mol of substance
define resonance structure
one of the two or more equally valid electron dot structures of a molecule or polyatomic ion
define molecular orbital
an orbital that applies to the entire molecule
define bonding orbital
a molecular orbital that can be occupied by 2 electrons of a covalent bond
define sigma bond
a bond formed when 2 atomic orbitals combine to form a molecular orbital that is symmetrical around the axis, which connects two atomic nuclei
define pi bond
a covalent bond in which the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms
define tetrahedral angle
a bond angle of 109.5 degrees that results when a central atom forms four bonds directed toward the center of a regular tetrahedron
define VSEPR Theory
valence-shell electron-pair repulsion theory: because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible
define hybridization
the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals
define nonpolar covalent bond
a covalent bond in which the electrons are shared equally by the two atoms
define polar covalent bond (polar bond)
a covalent bond between atoms in which the electrons are shared unequally
define polar molecule
a molecule in which one side of the molecule is slightly negative and the opposite side is slightly positive
define dipole
a molecule that has two poles, or regions, with opposite charges
define van de waals forces
the two weakest intermolecular attractions - dispersion interactions and dipole forces
define dipole interaction
intermolecular forces resulting from the attraction of oppositely charged regions of polar molecules
define dispersion force
attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces
these are the weakest interactions between molecules
define hydrogen bond
attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom
define network solid
a solid in which all of the atoms are covalently bonded to each other
what information does a molecular formula provide?
it shows how many atoms of each element a substance contains
what representative units define molecular compounds and ionic compounds?
molecular compounds = a molecule
ionic compounds = formula unit
what is the result of electron sharing in covalent bonds?
to attain the electron configuration of a noble gases
atoms also form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons
how are coordinate covalent bonds different from other covalent bonds?
in a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms
what are some exceptions to the octet rule?
the rule can’t be satisfied in molecules whose total number of valence electrons is an odd number
there are molecules in which an atom has less, or more, than a complete octet of valence electrons
how is the strength of a covalent bond related to its bond dissociation energy?
a large bond dissociation energy corresponds to a strong covalent bond
how are resonance structures used?
chemists use resonance structures to envision the bonding in molecules that cannot be adequately described by a single structural formula
how are atomic and molecular orbitals related?
just like an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole
what do scientists use the VSEPR theory for?
to explain the 3-D shape of molecules
in what ways is orbital hybridization useful in describing molecules?
it provides information about both molecular bonding and molecular shape
how do electronegativity values determine the charge distribution in a polar bond?
more electronegative atoms attract electrons more strongly and gains a slightly negative charge
the less electronegative atom has a slightly positive charge
what electronegativity difference range applies to nonpolar covalent bonds?
0.0-0.4
what electronegativity difference range applies to moderately polar covalent bonds?
0.4-1.0
what electronegativity difference range applies to very polar covalent bonds?
1.0-2.0
what electronegativity difference range applies to ionic bonds?
≥ 2.0
how do the strengths of intermolecular attractions compare with ionic and covalent bonds?
intermolecular attractions are weaker than either ionic or covalent bonds
why are the properties of covalent compounds so diverse?
because of widely varying intermolecular attractions
characteristics of ionic compounds? (7)
representative unit? bond formation? type of elements? physical state? melting point? solubility in water? good/bad conductors of electric current?
- the representative unit is a formula unit
- the bond formation is a transfer of electrons
- the type of elements are metallic and nonmetallic
- the physical state is a solid form
- the melting point is very high
- the solubility in water is usually high
- they are good conductors of electric current
characteristics of molecular compounds? (7)
representative unit? bond formation? type of elements? physical state? melting point? solubility in water? good/bad conductors of electric current?
1 molecule
- sharing electrons b/t atoms
- nonmetallic
- solid, liquid, or gas
- low
- high to low
- poor to nonconductors
where are the electrons in covalent bonds?
in molecular orbitals - atomic orbitals that supply an area for electrons to be shared
difference between linear and bent shapes?
linear doesn’t have any lone paired electrons; lone paired electrons make the linear shape bend, therefore, it’s bent
Weakest electronegative element?
What is it’s value?
Cesium - 0.7 –> Least tendency to attract electrons
Strongest electronegative element?
What is it’s value?
Fluorine - 4.0 –> has strong tendency to attract electrons
