Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
67 Cards in this Set
- Front
- Back
|
Covalent Compounds
|
most compounds we come in contact with in our lives are covalent compounds
|
|
|
covalent bonds
|
result from the sharing of electrons between two atoms
|
|
|
molecule
|
is a discrete group of atom,s held together by covalent bonds
|
|
|
H2
|
is a covalent bond the is very stale because it gives the two hydrogen two proton and two electrons which are stable like He which is a noble gas
|
|
|
A solid line between element symbols to represent a two-electron bond
|
H2
H : H H-H |
|
|
Diatomic molecule
|
contain just two elements in addition to hydrogen there are six others N2 O2 F2 Cl2 Br2 and I2 that are elements only
|
|
|
HF is
|
also a diatomic molecule
H has one electron F has seven electrons however the combination shares two electrons but leaves three unshared pairs |
|
|
Unshared pairs of electrons are called
|
nonbounded electron pairs or lone pairs
|
|
|
In covalent bonding
|
atoms share electrons to attain the electronic configuration of the noble gas closest to them in the periodic table
|
|
|
for a group of elements to be especially stable they must
|
process an octet of electrons in their outer shell
|
|
|
Covalent bonds forms when
|
two nonmetals combine or when a metalliod bonds to a nonmetal
|
|
|
covalent bonding
|
is preferred with elements in the middle of the periodic table
|
|
|
Lewis structure
|
electron-dot structures for molecules ---show the location of all valence electrons in a molecule both shared in bonds and unshared
|
|
|
atoms with one, two, or three valence electrons generally
|
form one,two, or three bonds
|
|
|
atoms with four or more valence electrons form
|
enough bonds to give an octet, thus, for atoms with four or more valence electrons ----predicted number of bonds = 8 number of valence electrons
|
|
|
a molecular formula shows
|
the number and identity of all of the atoms in a compound
|
|
|
a Lewis structure in contrast, shows
|
the connectivity between the atoms, as well as where all the bonding and nonbonding valence electrons reside
|
|
|
3 rules to drawing Lewis Structures
|
Draw only the valence electrons
give every maingroup element (except hydrogen) an octet of electrons give Hydrogen two electrons |
|
|
Multiple bonds
|
we must convert two lone pairs to two bonding pairs of electrons and form a triple bond
|
|
|
a triple bond
|
contains six electrons in three two-electron bonds
|
|
|
A double bond contains
|
four electrons in a two-electron bonds
|
|
|
after placing all electrons in bonds and lone pairs
|
to form multiple bond if an atom does not have an octet
|
|
|
exceptions to the octet rule
|
Hydrogen is the notable exception because it accommodates only two electrons in bonding--also Boron in group 3A and elements in the third row and later in the periodic table particularly phosphorous and sulfur
|
|
|
Elements below the third row have
|
empty d orbitals--PCL and H2S follow the octet rule but H2SO4 sulfuric acid and H3PO4 phosphoric acid have 12 and 10 electrons respectively
|
|
|
Lewis Structures for ions that contain covalent bonds--that is polyatomic ions
|
we must take the charge into account
Add one electron for each negative charge. Subtract one electron for each positive charge. |
|
|
Resonace structures are
|
Lewis structures having the same arrangement of atoms but a different arrangement of electrons
|
|
|
Two resonance structures differ
|
in the location of multiple bonds and the position of lone pairs
|
|
|
Neither resonance structure is
|
an accurate representation of the molecule. it is called a hybrid
|
|
|
Resonance
|
stabilizes the molecule
|
|
|
We say a molecule or ion that has two or more resonances structures is
|
resonance-stabilized
|
|
|
Ozone
|
O3 it protects the earth from ultraviolet light a decrease in ozone would mean an increase in skin cancer and eye cataracts
|
|
|
Naming Covalent compounds
|
h2o is water
NH3 is ammonia however other covalent compounds with two elements are named to indicate and identify the number of elements they contain |
|
|
NO2
|
name the first nonmetal by is element name and the second using the suffix -ide
Add prefixes to show the number of atoms in each element Nitrogen dioxide |
|
|
N2O4
|
dinitrogentetroxide
|
|
|
1
2 3 4 5 |
mono
di Tri Tetra penta |
|
|
6
7 8 9 10 |
hexa
hepta octa nona deca |
|
|
Molecular structure
|
Lewis structure does not determine shape but how connected--- H2O is it bent or straight
|
|
|
A group is either an atom or a lone
|
pair of electrons
|
|
|
Valence shell electron repulsion theory or VSEPR
|
VSEPR is based on the fact that electrons pairs repel each other
The most stable arrangement keeps these groups as far away from each other as possible |
|
|
An atom surrounded by two groups is
|
linear and has a bond angle of 180 degrees
|
|
|
an atom surrounded by three groups is
|
trigonal planar and has bond angles of 120 degrees
|
|
|
an atom surrounded by four groups is
|
has bond angles of 109.5 degrees and is called tetrahedral
|
|
|
Any atom surrounded by two groups is
|
linear and has a bond angle of 180 degrees--ignore multiple bonds in predicting geometry. Count only atoms and lone pairs
|
|
|
Any atom surrounded by three groups is
|
trigonal planar and has bonds angles of 120 degrees
|
|
|
Any atom surrounded by four groups is
|
tetrahedral and has bond angles of approximately 109.5 degrees
|
|
|
Drawing a tetrahedral
|
a solid line is used for bonds in the plane
a wedge for a bond in front of the plane a dashed line is used for the bond behind the plane |
|
|
NH3 ammonia
|
is drawn as a trigonal pyramid
.. H-N-H I H |
|
|
H2O is bent
|
..
H-O-H .. |
|
|
A group can also be lone pair
|
of electrons
|
|
|
Electronegativity
|
is a measure of an atom's attraction for electron in a bond.
tells us how much a particular atom wants electrons |
|
|
Electronegetivity
|
increases across a row of the periodic table as the nuclear charge increases (excluding the noble gases)
|
|
|
Electronegetivity
|
decreases down a column of the periodic table as the atomic radius increases, pushing the valence electrons farther from the nucleus
|
|
|
Ectronegegativity values are used as a guideline to indicate whether the electrons in a bond are
|
equally shared or unequally shared between two atoms
|
|
|
When two electrons are equally shared the bond is
|
non-polar thus Carbon-carbon bonds is nonpolar The same is true whenever two atoms having similar electronegativity are bonded together like C-H is also considered non-polar
|
|
|
Bonding between atoms of different electronegativity results in the
|
unequal sharing of sharing of electrons for example, in a C-o bond the electrons are pulled away fro C towards the element of higher electronegativity O the bond is polar
|
|
|
The symbol
|
is given to the less electronegative atom
|
|
|
The Symbol
|
is given to the more electronegative atom
|
|
|
Electronegativity Difference
Less than 0.5 units 0.5 - 1.9 1.9 and greater |
Bond type Electron sharing
nonpolar equally shared polar covalent unequally shared electrons are transfered from less electronegative to more |
|
|
Dipole
|
the bond is polar or polar covalent it is a dipole that is aseperation of charge
|
|
|
A molecule with no polar bonds is a
|
nonpolar molecule
|
|
|
a molecule with one polar bond is a
|
polar molecule
|
|
|
if the individual bond dipoles do not cancel
|
the molecule is polar
|
|
|
if the individual bond dipoles cancel
|
the molecule is nonpolar
|
|
|
a molecule with one polar bond is a
|
polar molecule
|
|
|
if the individual bond dipoles do not cancel
|
the molecule is polar
|
|
|
if the individual bond dipoles cancel
|
the molecule is nonpolar
|
|
|
Identify all polar bonds based on negativity differences
Determine the shape around individual atoms by counting groups decide if individual dipoles cancel or reinforce |
list
|
