how many electrons are shared in a single covalent bond?
2
in what diatomic molecule are the atoms joined by a triple covalent bond?
N2
how many covalent bonds can one carbon atom form?
4
what is shown by the structural formula of a molecule or polyatomic ion?
the arrangement of the bonded atoms
what is shown by the molecular formula of a molecule or polyatomic ion?
the number of each element present
what type of bond would a bond formed between a carbon atom and an oxygen atom most likely be?
a covalent bond
how can you identify how many atoms there are in a molecule in total?
add up all the subscripts
why do atoms form double or triple bonds?
because they can attain a noble gas configuration by sharing two pairs or three pairs of electrons
what tells you the number of atoms in a single element?
the subscript
how are atomic and molecular orbitals related?
just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole
what are molecular orbitals?
orbitals that apply to the entire molecule
what is a bonding orbital?
a molecular orbital that can be occupied by two electrons of a covalent bond
when is a sigma bond formed?
when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting two atomic nuclei
what do covalent bonds generally result from?
an imbalance between the attractions and repulsions of the nuclei and electrons involved
in stigma bonds, what do the nuclei and electrons attract and repel?
- nuclei and electrons attract each other
- nuclei repel other nuclei
- electrons repel other electrons
what orbitals can also overlap to form molecular orbitals?
p orbitals
where is there a high probability of finding a pair of electrons?
between the positively charged nuclei of the two elements
what do the side-by-side overlap of atomic p orbitals produce?
pi molecular orbitals
what is a pi bond?
the bonding electrons are most likely to be found in sausage-shaped regions about and below the bond axis of the bonded atoms
why do pi bonds tend to be weaker than sigma bonds?
because atomic orbitals in pi bonding overlap less than in sigma bonding
how can a drawing show where an electron is most likely to be found?
drawing can show molecular orbitals, which are the areas where bonding electrons are most likely to be found
in molecules with sigma bonds, where are the shared electrons most likely to be found?
in sigma bonds, bonding electrons are most likely to be found between the positively charged nuclei of the atoms bonded together
what do scientists use the VSEPR theory for?
in order to explain the three-dimensional shape of molecules, scientists use valence-shell electron-pair repulsion theory (VSEPR theory)
what is the tetrahedral angle?
all the angles are 109.5 degrees
what is the VSEPR theory?
states that the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible
what are also important in predicting the shapes of molecules?
unshared pairs
what causes valence-electron pairs to stay as far apart as possible?
the repulsion between electron pairs due to their negative charges cases valence-electron pairs to stay as far apart as possible
in what ways is orbital hybridization useful in describing molecules?
orbital hybridization provides information about both molecular bonding and molecular shape
what does the VSEPR theory not explain?
does not help much in describing the types of bonds formed
what happens in hybridization?
several atomic orbitals mix to form the same total number of equivalent hybrid orbitals
during hybridization, what does the extent of the overlap usually result in?
strong covalent bonds
what are the three types of covalent bonds?
single
double
triple
how many hybridized orbitals form when one 2s orbital is hybridized with three 2p orbitals?
four sp^3 orbitals form
how do electronegativity values determine the charge distribution in a polar bond?
the more electronegative atom attracts more strongly and gains a slightly negative charge. the less electronegative atoms has a slightly positive charge
how do covalent bonds differ?
in terms of how the bonded atoms share the electrons
what does the character of the molecule depend on?
the kind and number of atoms joined together
what do the features of a covalent bond determine?
the molecular properties
what are the bonding pairs of electrons in covalent bonds pulled between?
the nuclei of the atoms sharing the electrons
when is a nonpolar covalent bond formed?
when the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally to form these bonds
what is a polar covalent bond?
a covalent bond between atoms in which the electrons are shared unequally
what is true about the higher the electronativity value is, then...?
then the greater the ability of an atom to attract electrons to itself
what are the partial charges of electrons shown as?
clouds of electron density
what is the symbol that represents the polar nature of the bond?
arrow with a plus at the end
what does the electronegativity difference between two atoms tell you?
what kind of bond is likely to form
what is the most probable type of bond for atoms with the electronegativity difference range of 0.0 - 0.4?
nonpolar covalent
what is the most probable type of bond for atoms with the electronegativity difference range of > 0.4 - 1.0?
moderately polar covalent
what is the most probable type of bond for atoms with the electronegativity difference range of > 1.0 - 2.0?
very polar covalent
what is the most probable type of bond for atoms with the electronegativity difference range of > 2.0?
ionic
what type of elements describe polar covalent bonds?
metal and nonmetal
as the electronegativity difference between two atoms increases...
the polarity of the bond increases
as the electronegativity difference between two atoms decreases...
the polarity of the bond weakens
what does the presence of a polar bond in a molecule often do to the molecule?
makes the entire molecule polar
what is a polar molecule?
one end of the molecule is slightly negative, and the other end is slightly positive
what is a dipole?
a molecule that has two poles
- aka dipolar molecule
what happens to polar molecules when they are placed between oppositely charged plates?
they tend to become oriented with respect to the positive and negative plate
what does the effect of polar bonds on the polarity of an entire molecule depend on?
the shape of the molecule and the orientation of the polar bonds
what is the difference between an ionic bond and a very polar covalent bond?
two atoms will form an ionic bond rather than a very polar covalent bond if the two atoms have a slightly higher difference in electronegativity - a difference of more than 2.0. There is no sharp boundary between ionic and covalent bonds.
how do the strengths of intermolecular attractions compare with ionic and covalent bonds?
intermolecular attractions are weaker than either ionic or covalent bonds
what are intermolecular attractions responsible for?
determining whether a molecular compound is a gas, a liquid, or a solid at a given temperature
what are van der Waals forces?
the two weakest attractions between molecules
what do van der Waals forces consist of?
dipole interations and dispersion forces
when do dipole interactions occur?
when polar molecules are attracted to one another
in dipole interactions, where does the electrical attraction occur between?
the oppositely charged regions of polar molecules
how are dipole interactions different from ionic bonds?
dipole interactions are much weaker than ionic bonds
what is the slightly negative region of a polar molecule weakly attracted to?
the slightly positive region of another polar molecule
what are dispersion forces?
the weakest of all molecular interactions, are caused by the motion of electrons
- they occur even between nonpolar molecules
when does the strength of dispersion forces generally increase?
as the number of electrons in a molecule increases
what does the dipole interactions in water produce?
an attraction between water molecules
what does the positive region of one water molecule attract?
the negative region of another water molecule
what is the strong bond holding together the positive and negative molecules in water called?
a hydrogen bond
what are hydrogen bonds?
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
what bonds are the strongest of the intermolecular forces?
hydrogen bonds
why are hydrogen bonds important?
they are the strongest of the intermolecular forces and are extremely important in determining the properties of water and biological molecules such as proteins
why are the properties of covalent compounds so diverse?
the diversity of physical properties among covalent compounds is mainly because of widely varying intermolecular attractions
what do the physical properties of a compound depend on?
the type of bonding it displays - in particular, on whether it is ionic or covalent
what is different about the melting and boiling points of most compounds composed of molecules to those of ionic compounds?
they are low compared with those of ionic compounds
what is true about the weak attractions in most solids formed by molecules?
only the weak attractions between molecules need to be broken
what are network solids?
solids in which all of the atoms are covalently bonded to each other
- aka network crystals
what is an example of a network solid?
diamond
what is the representative unit of an ionic compound?
formula unit
what is the representative unit of a molecular compound?
molecule
what is the bond formation of an ionic compound?
transfer of one or more electrons between atoms
what is the bond formation of a molecular compound?
sharing of electron parts between atoms
what are the types of elements in ionic compounds?
metallic and nonmetallic
what are the types of elements in molecular compounds?
nonmetallic
what is the physical state of an ionic compound?
solid
what is the physical state of a molecular compound?
solid, liquid, or gas
what is the melting point of an ionic compound?
high (usually above 300 degrees C)
what is the melting point of a molecular compound?
high (usually below 300 degrees C)
how soluble are ionic compounds in water?
usually high
how soluble are molecular compounds in water?
high to low
what is the electrical conductivity of aqueous solution in ionic compounds?
good conductor
what is the electrical conductivity of aqueous solution in molecular compounds?
poor to nonconducting
why do network solids take so much more heat to melt than most covalent compounds?
melting a network solid requires breaking covalent bonds throughout the solid. Melting most covalent compounds only requires breaking the weak attractions between molecules