COMPOUNDS AND BONDING.

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 bond Polar molecule Dipole Van der Waals Forces Dispersion forces Dipole interactions Hydrogen bonds

Van der Waals forces Consist of two kinds
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

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 I. COMPOUND: A. The Chemistry meaning:

Materials made from atoms of two or more combined elements.
Notes 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.

3. Na + Cl  NaCl (table salt) which we eat with little harm.
Notes 3. Na + Cl  NaCl (table salt) which we eat with little harm.

II. BONDING: A. The Chemistry meaning:
Notes II. BONDING: A. The Chemistry meaning:

Interaction between atoms that results in the formation of a compound.
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. exothermic 2. Energy has to be applied to break the bond. endothermic

3. The bond energy is the lowest potential energy for the compound.
Notes 3. The bond energy is the lowest potential energy for the compound.

D. IONIC BONDS: Atoms gain or lose electrons
Notes D. IONIC BONDS: Atoms gain or lose electrons

1. Usually happens between a metal and a nonmetal.
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)

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 An ionic bond forming calcium phosphide A covalent bond forming carbon monoxide (make sure Carbon and Oxygen both have 8 valence electrons available to them)

Hybrid 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

LiF is ionic (metal + non-metal)
Overlapping orbitals Draw orbital diagrams for F + F, H + O, Li + F 1s 2s 2p 1s 2s 2p F2 1s H2O 1s 2s 2p 1s 1s 2s 1s 2s 2p LiF is ionic (metal + non-metal)

Lewis diagrams Draw 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

Ionic bonding Recall: Ionic bonding involves 3 steps:
1) loss of e-, 2) gain of e-, 3) +ve, -ve attract e– 1) 2) Na Cl 3) Cl– Na+ Cl– Na+ This can be represented via Lewis diagrams… Diagram the reaction between Li + Cl and Mg + O (PE 3)

The octet rule (ionic compounds)
Draw Li + Cl and Mg + O (PE 3, pg. 230) Li Cl [ Cl ]– [Li]+ O Mg [ O ]2– [Mg]2+ 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 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) Cl O N H H H H Cl Cl C Cl H2O H H NH3 Cl [ F ]2– [Mg]2+ HCl CCl4 MgF2 - Ionic Note bonds can also be drawn with a dash to represent two electrons

E. COVALENT BONDS: Atoms share electrons rather than losing them
Notes 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.

Structure Determination by VSEPR
Water, H2O The electron pair geometry is TETRAHEDRAL 2 bond pairs 2 lone pairs The molecular geometry is BENT.

Answer the following Is the electronegativity values of nonmetallic elements greater or less than the electronegativity values of metallic elements? In a polar covalent bond does the more electronegative atom have a slight positive or negative charge?

How many valence electrons do Oxygen and Sulfur have?
How many valence electrons will Nitrogen gain or lose to be isoelectronic with a noble gas? 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 Pairs

Lone pairs Thus far we have considered (built) only structures where there are no free electrons around the central atom H C H C Vs. H N H N or or 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…

Variations 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 Bipyramidal
AX5 is trigonal bipyramidal AX4E is unsymmetrical tetrahedron AX2E3 is linear AX3E2 is T-shaped

Variations on Octahedral Shape
AX6 is octahedral AX5E is square pyramidal AX4E2 is square planar For more lessons, visit

Answer these Given elements with electronegativities as follows: L: 1.9, M:3.0, Q: 0.9, R: 2.5 Which combination would be the least polar? Which combination would be the most polar? 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 formula 18. 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
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

Notes IV. THE OCTET RULE: atoms form bonds to achieve a noble gas configuration

VII. ELECTRON DOT SYMBOLS or Lewis electron dot symbols
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.

V. Bond formation is predicted by two observations:
Notes V. Bond formation is predicted by two observations:

A. Noble gases are unreactive and form very few compounds.
Notes A. Noble gases are unreactive and form very few compounds.

B. A filled outermost orbital is very stable
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.

A. Developed by G. N. Lewis in 1916
Notes A. Developed by G. N. Lewis in 1916

Notes B. The element symbol represents 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.

D. Imagine a box around the symbol
Notes D. Imagine a box around the symbol F Fluorine 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 . .

2. Then pair the dots on each side
Notes 2. Then pair the dots on each side . . . F . . . .

E. Exact placement of dots depends upon how the symbol is being used.
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 . . C . . . . O . . .

. . Notes . . Cl . . . . . . . Ne . . . .

Notes VIII. Writing electron dot structures of compounds: answer these questions:

A. How many kinds of atom are in the compound?
Notes A. How many kinds of atom are in the compound?

Notes 1. Determine this from the compound formula MgCl2 = 2 types of atoms – Magnesium and Chlorine

B. How many valence electrons are available?
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.

4. Mg is in group 2A = 2 valence electrons
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.

C. What is the skeleton structure?
Notes C. What is the skeleton structure?

1. The skeleton structure shows which atoms are bonded to each other.
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.)

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 Cl add in the 14 electrons
. . . . . . . . . . . . Cl Mg Cl . . . .

2. Hydrogen is an exception it will have 2 electrons.

Practice: Do each Lewis dot diagram

NUMBER OF EACH TYPE OF ATOM
MOLECULE: H2O NUMBER OF EACH TYPE OF ATOM H = 2 O = 1

NUMBER OF VALENCE ELECTRONS FOR EACH ATOM

TOTAL VALENCE ELECTRONS
H: 21=2 + O: 16=6 8

SKELETON STRUCTURE H O H

LEWIS DOT STRUCTURE . . . . . . H O H . .

MOLECULE: CaCL2 NUMBER OF EACH TYPE OF ATOM Ca = 1 Cl = 2

Ca = 2 Cl = 7

Ca: 12= 2 + Cl: 27=14 16

SKELETON STRUCTURE Cl Ca Cl

LEWIS DOT STRUCTURE . . . . . . . . . . . . Cl Ca Cl . . . .

MOLECULE: H2S NUMBER OF EACH TYPE OF ATOM H = 2 S = 1

H: 21=2 + S: 16=6 8

SKELETON STRUCTURE H S H

LEWIS DOT STRUCTURE . . . . . . H S H . .

MOLECULE: SiF4 NUMBER OF EACH TYPE OF ATOM Si = 1 F = 4

Si = 4 F = 7

Si: 14= 4 + F: 47=28 32

SKELETON STRUCTURE F F Si F

. . . . LEWIS DOT STRUCTURE . . . . . . . . F F Si F . . . . . . . . . . . . . . . . . . . .

MOLECULE: CCl4 NUMBER OF EACH TYPE OF ATOM C = 1 Cl = 4

Cl = 7

+ Cl: 47=28 32

SKELETON STRUCTURE Cl Cl C Cl

. . . . LEWIS DOT STRUCTURE . . . . . . . . Cl Cl C 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
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

COMPOUNDS AND BONDING.

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