JLH Chem Ch 4 Flashcards
Most compounds that we come into contact with in our daily lives are what?
covalent compounds
When two hydrogen atoms with ___ electron each combine, they form a ________ bond that contains ___ electrons.
When two hydrogen atoms with one electron each combine, they form a covalent bond that contains two electrons.
When two hydrogen atoms bond they form the hydrogen molecule, H2. This is an especially stable arrangement, because why?
the shared electrons (from each hydrogen) give each hydrogen atom the noble gas configuration of helium.
covalent bond
two electron bond in which the bonding atoms share valence electrons
molecule
compound held together by covalent bonds
what ways can a two-electron bond be drawn as?
What is a diatomic molecule?
molecules composed of only two atoms
What are the 7 diatomic Elements?
What is an example of a diatomic molecule that has two different atoms?
Hydrogen fluoride (HF)
- Remember, Hydrogen is a non-metal*
- called heteronuclear diatomic molecules. When atoms are not identical, the molecule forms by combining atomic orbitals of unequal energies. The result is a polar bond in which atomic orbitals contribute unevenly to each molecular orbital.*
What are unshared electron pairs called?
non-bonded electron pairs
or
lone pairs
Draw an electron-dot symbol to show how a hydrogen atom and a chlorine atom form the diatomic molecule HCL.
H is surrounded by 2 electrons (same as He)
Cl is surrounded by eight electrons (same as Ar)
When do two atoms form covalent bonds rather than ionic bonds?
Covalent bonds are formed when two nonmetals combine or when a nonmetal and a metalloid bond.
Nonmetals do not easily lose electrons, and as a result, one nonmetal does not readily transfer an electron to another nonmetal.
3 examples of covalent molecules in which each main group element is surrounded by 8 electrons.
CH4 (methane)
NH3 (ammonia)
H2O (water)
Lewis dot structure
An electron-dot structure for a molecule that shows the location of all valence electrons in the molecule, both the shared electrons in bonds and the nonbonded electron pairs.
Atoms with one, two, or three valence electrons generally form how many bonds?
one, two, or three bonds, respectively
How many bonds do atoms with 4 or more valence electrons form?
enough bonds to give an octet.
How many covalent bonds are predicted for each atom:
B
N
B has 3 valence electrons. Thus, it is expected to form 3 bonds
N has 5 valence electrons. Because it contains more than 4 valence electrons, it is expected to form 8-5=3 bonds.
how many covalent bonds are predicted for each atom:
F
Si
F: 1 bond
Si: 4 bonds
Fill in the lone pairs
Fill in the lone pairs
fill in the lone pairs
Living organisms are a sea of covalent molecules. Name some covalent molecules in the body.
Water (major component of the body)
Proteins that compose muscle
Carbohydrates that are metabolized for energy
stored fat
DNA
Hemoglobin
What covalent compound is a building block of proteins that compose heart muscle?
Glycine
- Hydrogen = White.
- Oxygen = Red.
- Chlorine = Green.
- Nitrogen = Blue.
- Carbon = Grey/Black.
- Sulphur = Yellow.
- Phosphorus = Orange
What does a molecular formula show us?
The number and identity of all of the atoms in a covalent compound
Does not tell us what atoms are bonded to each other.
The molecular formula NH3 for ammonia shows that ammonia contains one nitrogen atom and three hydrogen atoms, but it does not tell us that ammonia has three covalent nitrogen-hydrogen bonds and that the N atom has a lone pair. What type of structure shows the connectivity between the atoms?
Lewis dot structure
What are the 3 general rules for drawing Lewis structures?
- Draw only the valence electrons
- Give every main group element (except hydrogen) an octet of electrons
- Give each hydrogen 2 electrons
While drawing a Lewis structure for a diatomic molecule with one bond is straightforward, drawing Lewis structures for compounds with 3 or more atoms is easier if you follow a general procedure. What is this general procedure?
Arrange the atoms next to each other that you think are bonded together. (always place hydrogens & halogens on the periphery)
However many electrons needed to form an octet on an element is usually how many bonds that element will form. (N generally forms 3 bonds-place 3 atoms around N, C generally forms 4 bonds-place 4 atoms around C)
How do you arrange the electrons around the atoms in a Lewis structure?
Place one bond between every 2 atoms, giving 2 electrons to each H and no more than 8 to all other main group atoms
Use all remaining electrons to fill octets with lone pairs, beginning with atoms on the periphery.
When drawing a Lewis structure, if all valence electrons are used and an atom does not have an octet, what do you do?
Convert one lone pair to one bonding pair of electrons for each 2 electrons needed to complete an octet. This forms double or triple bonds.
How many electrons does a single covalent bond contain?
double bond?
triple bond?
Single bond: 2 e-
Double bond: 4 e-
Triple bond: 6 e-
draw a Lewis structure for chloromethane, CH3CL
(Since C needs 4 e-) Place C in the center (H and Cl only need 1 e-) so place them on the periphery
Count electrons (C has 4e-, H has 3e- because there is 3 Hs, Cl has 7e-, making a total 14 e-)
Add the bonds & lone pairs
Draw a Lewis structure for HBr
Draw a Lewis structure for CH3F
Draw a Lewis structure for CH2CL2
Draw a Lewis structure for methanol (CH4O)
C needs 4 atoms around it
O needs 2 atoms around it
14 total valence electrons
draw a Lewis structure for dimethyl ether (C2H60) with the given arrangement of atoms
Sometimes it is not possible to give every main group element (except hydrogen) an octet of electrons by placing only single bonds in a molecule. For example, in drawing a Lewis structure for N2, each N has 5 valence electrons, so there are 10 electrons to place. If there is only one N-N bond, adding lone pairs gives one or both N’s fewer than eight electrons. How do we fix this?
We must convert a lone pair to a bonding pair of electrons to form a multiple bond. Because we have 4 fewer electrons than needed, we must convert 2 lone pairs to 2 bonding pairs of electrons and form a triple bond.
Draw a Lewis structure for ethylene (C2H4)
Draw a valid Lewis structure for HCN
Draw a Lewis structure for formic acid (CH2O2) with the following arrangement of atoms:
Elements in group 3A of the periodic table, such as boron, do not have enough valence electrons to form an octet in a neutral molecule. What is the Lewis structure for BF3?
only 6 electrons around B
I’m just not sure why BF3 does not get a double bond (maybe because B can only have 3 bonds)
Another exception to the octet rule occurs with some elements located in the 3rd row & later. Explain-
these elements have empty d orbitals available to accept electrons, and thus they may have more than 8 electrons around them.
Most common elements in this category are phosphorus & sulfur, which can have 10 or 12 e- around them.