compounds and bonding
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COMPOUNDS AND BONDING. Objectives 1. Identify characteristics in atoms involved in chemical bonding Compare the physical and chemical properties of ionic and covalent compounds Compare the arrangement of atoms in molecules, ionic crystals, polymers, and metallic substances. - PowerPoint PPT PresentationTRANSCRIPT
COMPOUNDS AND
BONDING
Objectives 1
• Identify characteristics in atoms involved in chemical bonding
• Compare the physical and chemical properties of ionic and covalent compounds
• Compare the arrangement of atoms in molecules, ionic crystals, polymers, and metallic substances
Vocabulary: define in your journal
• Valence electrons
• Electron dot structures
• Octet rule
• Ionic bond
• Anion
• Cation
• Metallic bonds
• Covalent bond
• Structural formula
• Unshared pairs
• Double covalent bonds
• Triple covalent bonds
• Coordinate covalent bonds
• Bonds
• Bond dissociation energy
• Resonance structures
• Nonpolar covalent bond
• Polar covalent bond
• Polar bond
• Polar molecule
• Dipole
• Van der Waals Forces
• Dispersion forces
• Dipole interactions
• Hydrogen bonds
Van der Waals forces
Consist of two kinds1. Dispersion forces: weak force caused by
the motion of electrons, increases with increasing electrons
Seen in diatomic molecules, weak in fluorine and chlorine making them gases
Stronger in bromine causing it to be a liquid
2. Dipole interactions: caused by attraction of polar molecules for each other; occurs between weakly positive and negative molecules
Water is held together by the dipole interactions of adjacent oxygen (-) and hydrogen (+) atoms when water molecules come close together
Hydrogen bonds (+) are strongest of dipole interactions
I. COMPOUND: A. The Chemistry meaning:
Notes: Handout
Materials made from atoms of two or more combined
elements.
Notes
B. Compounds have properties that are unlike the
elements that form them.
Notes
1. Na (Sodium) is a silvery metal that reacts violently
with water.
2. Cl (Chlorine) is a green gas that can kill any animal.
Notes
3. Na + Cl NaCl (table salt) which we eat with little harm.
Notes
II. BONDING:A. The Chemistry meaning:
Notes
Interaction between atoms that results in the formation of
a compound.
Notes
B. CHEMICAL BOND: Strong attractive force between atoms
or ions in a compound.
Notes
C. BOND ENERGY: Energy involved in the making and
breaking of chemical bonds.
Notes
1. Energy is released to make a bond.
exothermic2. Energy has to be applied to
break the bond. endothermic
Notes
3. The bond energy is the lowest potential energy for
the compound.
Notes
D. IONIC BONDS: Atoms gain or lose electrons
Notes
1. Usually happens between a metal and a nonmetal.
Notes
2. Ion - atom which has:a. Gained one or more
electrons - negative charge (anion)
b. Lost one or more electrons - positive charge (cation)
Notes
Lewis Dot Diagram
• Complete the handout Ionic Bonds and Covalent bonds
Quiz 1: Ionic and Covalent Bonds
Draw a Lewis dot diagram showing the following bonds
1.An ionic bond forming calcium phosphide
2.A covalent bond forming carbon monoxide (make sure Carbon and Oxygen both have 8 valence electrons available to them)
Hybrid orbitalsHybrid orbitals• Two overlapping orbitals form what is known
as a hybrid or molecular orbital• Just as in a s,p,d, or f orbital the electrons
can be anywhere in the orbital (even though the electron has started out in one atom, at times, it may be closer to the other nucleus)
• Each hybrid orbital has a specific shape • You do not need to know shapes• You need to know that hybrid orbitals exist
and that they are formed from overlapping orbitals
Overlapping orbitalsOverlapping orbitals• Draw orbital diagrams for F + F, H + O, Li + F
1s 2s 2p
1s2s2p
1s 2s 2p
1s
1s
F2
H2O
1s 2s 1s2s2p
LiF is ionic (metal + non-metal)
Lewis diagramsLewis diagramsDraw Lewis dot diagrams for Ne, Sb, Rb, F.
How many variations of the Lewis diagram for P can be drawn?
Ne Sb Rb F
P P P P
• Lewis diagrams follow the octet rule: atoms when forming ions, or bonding to other atoms in compounds have 8 outer electrons
• Q - How can the octet rule be explained?• A - s (2 e–) and p (6 e–) orbitals are filled
Cl– Na+ Cl–
Ionic bondingIonic bonding• Recall: Ionic bonding involves 3 steps:
1) loss of e-, 2) gain of e-, 3) +ve, -ve attract
Na Cl
e–1) 2)
3)
Na+
This can be represented via Lewis diagrams…• Diagram the reaction between Li + Cl and Mg + O (PE 3)
The octet rule (ionic compounds)The octet rule (ionic compounds)• Draw Li + Cl and Mg + O (PE 3, pg. 230)
Li Cl [ Cl ]–[Li]+
[ O ]2–[Mg]2+OMg
• Note also that the charge on an ion can be determined by the number of places removed from a noble gas (Ca, N, Al?)
• Ca2+, N3-, Al3+
Covalent bondingCovalent bonding• Covalent bonds can also be shown via Lewis
diagrams - E.g draw Lewis diagrams showing the combination of 1) H+Cl, 2) C+Cl, 3) H+O, 4) Mg+F, 5) N+H, 6) Do PE 4 (pg. 234)
HCl
H Cl
CCl4
C
Cl
Cl
Cl
Cl H2OH O H
MgF2 - Ionic
[ F ]2– [Mg]2+
NH3
H N H
H
• Note bonds can also be drawn with a dash to represent two electrons
E. COVALENT BONDS: Atoms share electrons rather
than losing them
Notes
1. Usually between nonmetals
2. Sharing can be unequal causing the compound to seem to have a charge.
Notes
a. One nucleus is larger(has more protons)
and acts like a bigger magnet.(And because it has
a higher electronegativity)
Notes
b. The electrons spend more time around the larger
nucleus than around the smaller nucleus.
Notes
3. Water for example seems to have a charge, but it is a
covalent compound.
Notes
a. The oxygen nucleus is larger(has more protons)
and acts like a bigger magnet. (actually it has a higher
electronegativity)
Notes
b. The electrons spend more time around the oxygen nucleus than around the
hydrogen nuclei.
Notes
Structure Determination Structure Determination by VSEPRby VSEPR
Structure Determination Structure Determination by VSEPRby VSEPR
Water, HWater, H22OO The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL
The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL
The molecular The molecular geometry is geometry is BENTBENT..
The molecular The molecular geometry is geometry is BENTBENT..
H O H••
••
H O H••
••
2 bond 2 bond pairspairs
2 lone 2 lone pairspairs
Answer the following
1. Is the electronegativity values of nonmetallic elements greater or less than the electronegativity values of metallic elements?
2. In a polar covalent bond does the more electronegative atom have a slight positive or negative charge?
3. How many valence electrons do Oxygen and Sulfur have?
4. How many valence electrons will Nitrogen gain or lose to be isoelectronic with a noble gas?
5. What is the name of an ion that has gained electrons?
Types of covalent bonds(not on paper)
• Single covalent bond: a bond formed when a pair of electrons is shared between two atoms
• Double covalent bond: a bond formed when two pairs of electrons are shared between two atoms
• Triple covalent bonds: a bond formed when three pairs of electrons are shared between two atoms
• Coordinate covalent bond: a covalent bond formed when one atom contributes both bonding electrons
Answer the following
Double covalent bond electronegativity isoelectronic covalent bond triple covalent bond
• Attraction for a shared pair of electrons• Formed by sharing electrons• Having the same number of electrons• Sharing four electrons• Sharing six electrons
Pi Bond: caused by overlap of p orbitals
Hydrogen bonds
#11. Try this one
• Draw a structure for phosphate PO4-3
#12 Practice
• Mg + F2 --> Mg F2
- Draw a Bohr model showing the reaction
- Draw a Lewis dot diagram showing the reaction
- Draw a model of the reaction using the electron configuration diagrams including the boxes
#13. Try this
VSEPR: Lone PairsVSEPR: Lone Pairs
Lone pairsLone pairs• Thus far we have considered (built) only
structures where there are no free electrons around the central atom
• These electrons that are not involved in bonds are called “lone pairs”
• Essentially, they have the same influence on molecular structure as electron pairs in bonds
• The result is some weird shapes and names…
orVs.
orH C
H
H
H
H C H
H
H
H N H
H
H N H
H
Variations on Tetrahedral MoleculeVariations on Tetrahedral Molecule• The tetrahedral molecule is AX4
• Lone pairs can be indicated with AXYEZ, where Z is the number of lone pairs
• By replacing 1 bond with a lone pair the tetrahedral shape becomes “trigonal pyramidal”
• AX3E
• By replacing two bonds with lone pairs we get a “bent” (non-linear) shape (AX2E2 )
Variations on Trigonal BipyramidalVariations on Trigonal Bipyramidal• AX5 is trigonal
bipyramidal
• AX4E is unsymmetrical tetrahedron
• AX3E2 is T-shaped
• AX2E3 is linear
Variations on Octahedral ShapeVariations on Octahedral Shape• AX6 is octahedral
• AX5E is square pyramidal
• AX4E2 is square planar
For more lessons, visit www.chalkbored.com
Answer these
Given elements with electronegativities as follows: L: 1.9, M:3.0, Q: 0.9, R: 2.5
14. Which combination would be the least polar?
15. Which combination would be the most polar?
16. How many valence electrons in SO4-2?
Compounds
• Compounds are pure substances made of more than one kind of atom
• Obey the law of definite proportions by always combining in the same proportions by mass
• A molecule is a neutral group of atoms that act as a unit
• Compounds composed of molecules are molecular compounds– Tend to have relatively low melting and boiling
points– Many exist as gases or liquids at room
temperatures– Most are composed of two or more
nonmetallic elements– Examples: water and carbon dioxide
• Compounds composed of positive and negative ions are called ionic compounds– Arranged in orderly 3-dimensional pattern
– Each positive ion between two or more positive ions and at the same time each negative ion is between two or more positive ions.
– Are electrically neutral
– Most are crystalline solids at room temperature
– Usually formed from a metallic and nonmetallic element
– Example: sodium chloride (table salt)
Define the following as we go through the lesson
17. Chemical formula18. Molecular formula
19. Subscript
20. Ionic compound
21. Simplest formula
22. Formula unit
23 to 25. Describe ionic and molecular compound characteristics
Chemical Formulas
• Chemical formulas show the kinds and numbers of atoms in the smallest representative unit of the substance
• The chemical formula for a molecular compound is called the molecular formula– The number of atoms of each kind is
indicated by a subscript written after the formula
– Examples: water = H20, carbon dioxide = CO2
• Requires a diagram to show the arrangement of the atoms
• Ionic compounds are composed of equal amounts of each type of atom arranged in an orderly pattern
• Chemists use the simplest formula to represent an ionic compound
• Example: sodium chloride could be NaCl, Na2Cl2, Na3Cl3, etc., so the simplest formula, NaCl is used
• Formula unit is the lowest whole-number ratio of ions in an ionic compound
Characteristics of Ionic and Molecular Compounds
Characteristic Ionic Compound Molecular Compound
Representative unit
Formula unit Molecule
Type of elements Metallic combined with nonmetallic
Nonmetallic
Physical state Solid Solid, liquid or gas
Melting point High: above 300C Low: below 300C
IV. THE OCTET RULE: atoms form bonds to achieve a noble
gas configuration
Notes
VII. ELECTRON DOT SYMBOLS or Lewis electron
dot symbols
Notes
A. Each atom would then have 8 electrons in the outermost
energy level.
B. Hydrogen is an exception, it would have 2 electrons.
Notes
V. Bond formation is predicted by two
observations:
Notes
A. Noble gases are unreactive and form very few
compounds.
Notes
B. A filled outermost orbital is very stable
Notes
1. Helium has 2 valence electrons.
2. All the other noble gases have 8 valence electrons.
Notes
IV. Most stable compounds containing representative elements contain ions that have acquired an electron
configuration that is the same as the electron configuration of
a noble gas.
Notes
A. Developed by G. N. Lewis in 1916
Notes
B. The element symbolrepresents the nucleus and the core electrons
C. Dots represent the valence electrons - each dot is an electron
Notes
The number of valence electrons is the group number for all group A elements. (An element in group 2A has 2
valence electrons)
This statement is not on your paper.
Notes
D. Imagine a box around the symbol
FFluorine is in family 7A. It has 7 valence electrons
Notes
1. Place one dot on each side of the symbol until there is
one dot on each side.
F.
..
.
Notes
2. Then pair the dots on each side
.... .
.
.F
Notes
E. Exact placement of dots depends upon how the symbol is being used.
Notes
F. Try to group the dots so that the electron pairs are on opposite sides of the symbol to illustrate the way electrons
spread out around the nucleus.
Se.. . ...
Se = family 6A = 6 valence electrons
Notes
G. Do electron dot symbols for oxygen, chlorine, carbon and
neon:
O Cl C Ne
Notes
CO.
.
.. ...
. ..Notes
ClNe.. .
...
..
... ..
..Notes
VIII. Writing electron dot structures of compounds:
answer these questions:
Notes
A. How many kinds of atom are in the compound?
Notes
1. Determine this from the compound formula.
2. MgCl2 = 2 types of atoms –
Magnesium and Chlorine
Notes
B. How many valence electrons are available?
Notes
1. Use the position of each atom in the periodic table to
determine the number of valence electrons.
Notes
2. Group A families: use the family/group number.
3. Group B families: we are not doing these.
Notes
4. Mg is in group 2A = 2 valence electrons
Notes
5. Cl is group 7A = 7 valence electrons but there are two Cl, so multiply the valence number by the number of atoms in the formula 2 X 7 = 14 valence
electrons
Notes
6. Add up the total electrons for the compound
2 (from Mg) + 14 (from Cl) = 16valence electrons
Notes
7. Use the total number of valence electrons in the electron dot structure.
Notes
C. What is the skeleton structure?
Notes
1. The skeleton structure shows which atoms are bonded to
each other.
Notes
2. The single atom in the formula is usually the central atom.
3. Carbon always goes in the middle. (Even if there are more than one
carbon in the formula.)
Notes
Cl Mg Cl
D. Where do the dots go in the structure?
1. Place the dots around the element symbols so that each
symbol has 8 electrons.
SKELETON = Cl Mg Cladd in the 14 electrons
Cl ClMg .. ......
....
. ...
2. Hydrogen is an exception it will have 2 electrons.
Practice: Do each Lewis dot diagram
MOLECULE: H2ONUMBER OF EACH TYPE
OF ATOM
H = 2
O = 1
NUMBER OF VALENCE ELECTRONS FOR EACH
ATOM
H = 1
O = 6
TOTAL VALENCE ELECTRONS
H: 21=2+ O: 16=6
8
SKELETON STRUCTURE
H O H
LEWIS DOT STRUCTURE
H O H.. .. ....
MOLECULE: CaCL2NUMBER OF EACH TYPE
OF ATOM
Ca = 1
Cl = 2
NUMBER OF VALENCE ELECTRONS FOR EACH
ATOM
Ca = 2
Cl = 7
TOTAL VALENCE ELECTRONS
Ca: 12= 2+ Cl: 27=14
16
SKELETON STRUCTURE
Cl Ca Cl
LEWIS DOT STRUCTURE
Cl Ca Cl.. ....
...... ....
MOLECULE: H2SNUMBER OF EACH TYPE
OF ATOM
H = 2
S = 1
NUMBER OF VALENCE ELECTRONS FOR EACH
ATOM
H = 1
S = 6
TOTAL VALENCE ELECTRONS
H: 21=2+ S: 16=6
8
SKELETON STRUCTURE
H S H
LEWIS DOT STRUCTURE
H S H.. .. ....
MOLECULE: SiF4NUMBER OF EACH TYPE
OF ATOM
Si = 1
F = 4
NUMBER OF VALENCE ELECTRONS FOR EACH
ATOM
Si = 4
F = 7
TOTAL VALENCE ELECTRONS
Si: 14= 4+ F: 47=28
32
SKELETON STRUCTURE
FF Si F
F
LEWIS DOT STRUCTURE
FF Si F
F
. ......
. . .....
... ... ..
......
.. . .
MOLECULE: CCl4NUMBER OF EACH TYPE
OF ATOM
C = 1
Cl = 4
NUMBER OF VALENCE ELECTRONS FOR EACH
ATOM
C = 4
Cl = 7
TOTAL VALENCE ELECTRONS
C: 14= 4+ Cl: 47=28
32
SKELETON STRUCTURE
ClCl C Cl
Cl
LEWIS DOT STRUCTURE
ClCl C Cl
Cl
. ......
. . . ....
... ... ..
......
.. . .
XI. LIMITATIONS OF THE OCTET RULE:
A. The octet rule is a rule of thumb and compounds do
not obey rules.
B. Some compounds cannot be explained by the octet rule.
C. Nitric oxide (NO) has an odd number of valence
electrons (5 + 6 = 11) and does not satisfy the octet rule
and is not an ion.
D. Atoms without octets
1. Some stable compounds have a central atom without
an octet.
2. Boron trifluoride BF3 is stable and has been shown
experimentally to have only 6 electrons around the Boron
atom.
E. Some stable compounds have a central atom with more
than an octet of electrons.
1. Compounds synthesized from noble gases are an
example.
2. More than an octet is possible because of the larger
size of some central atoms.
3. Sometimes the bond includes electrons from the core electrons in addition to
the valence electrons.
F. Equivalent electron dot structures
1. Some compounds and polyatomic ions can have more
than one structure.
2. These are resonance structures.
3. Writing each of the possible structures and putting double headed arrows () between
the structures shows the resonance.
Molecular orbitals
• Bonding orbitals: molecular orbital with an energy lower than that of the atomic orbitals from which it is formed (all electrons seek lowest energy level)
• Sigma bond (): a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical along the axis connecting the two atomic nuclei
• Pi bond (): a bond in which the bonding electrons are most likely to be found in the sausage-shaped regions above and below the nuclei of the bonded atoms
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.
• Hybridization: several orbitals mix to form the same total number of equivalent hybrid orbitals
• ex: methane CH4 : One 2s orbital and three 2p orbitals of a carbon atom mix to form four sp3 hybrid orbitals. These four sp3 hybrid orbitals then overlap the 1s orbital of each hydrogen atom.
Face centered