Types of Bonding. Ionic Bonding occurs between metals and nonmetals. Covalent Bonding occurs between two or more nonmetals

Covalent Bonding Types of Bonding Ionic Bonding occurs between metals and nonmetals. Covalent Bonding occurs between two or more nonmetals. Metallic...
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Covalent Bonding

Types of Bonding Ionic Bonding occurs between metals and nonmetals. Covalent Bonding occurs between two or more nonmetals. Metallic Bonding occurs between metal atoms.

Molecular Compounds Covalent bonds are the bonds formed between atoms who are sharing electrons. A molecule is a neutral group of atoms joined together by covalent bonds.

A compound composed of molecules is a molecular compound. Molecular formula is the chemical formula for a molecular compound. See Pages Examples: CO2 or NH3

213 - 216

Molecular Compounds Diatomic molecules are molecules that consist of two atoms. Example: N₂, O2, F₂, Cl₂, Br₂, I₂, H₂

Properties of Molecular Compounds • Usually lower melting points than ionic compounds. • Usually lower boiling points than ionic compounds.

See Page 214

Representing Molecules

Hydrocarbons Molecular compounds that contain only carbon and hydrogen atoms.

H H H

H H H H H

H–C–C–C–C–C–C–C–C–H

H H H H H H H H

Examples of Hydrocarbons Chains

Branches

Rings

Hydrocarbons (Alkanes) Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane

CH₄ C₂H₆ C₃H₈ C₄H₁₀ C₅H₁₂ C₆H₁₄ C₇H₁₆ C₈H₁₈ C₉H₂₀ C₁₀H₂₂

General formula for alkanes

CnH2n+2

Hydrocarbons (Alkenes) Methene Ethene Propene Butene Pentene Hexene Heptene Octene Nonene Decene

CH2 C₂H4 C₃H6 C₄H8 C₅H10 C₆H12 C₇H14 C₈H16 C₉H18 C₁₀H20

General formula for alkenes

CnH2n

Hydrocarbons (Alkynes) Ethyne Propyne Butyne Pentyne Hexyne Heptyne Octyne Nonyne Decyne

C₂H2 C₃H4 C₄H6 C₅H8 C₆H10 C₇H12 C₈H14 C₉H16 C₁₀H18

General formula for alkynes

CnH2n-2

Polymers • Molecules composed of a regularly repeating structural sequence • Extended chain structures are formed from simple molecules

Protein

Isomers Compounds that have the same formula but a different structure

Pentane, C5H12

Isomers glucose

fructose

galactose

Naming Molecular Compounds (Other than hydrocarbons)

Prefixes Mono 1 Di 2 Tri 3 Tetra 4 Penta 5 Hexa 6 Hepta 7 Octa 8 Nona 9 Deca 10

Pg. 269

Rules for Naming Molecular Compounds Name the elements in the molecule and indicate the number of each using the prefixes. Ex. N2O5 dinitrogen pentaoxygen The suffix of the name of the second element is ‘-ide’. Ex. N2O5 dinitrogen pentaoxide

Rules for Naming Molecular Compounds The vowel at the end of a prefix is dropped when the element begins with a vowel. Ex. 1 oxygen would be monoxide not monooxide If just one atom of the first element is in the formula, omit the prefix mono-. Ex. CO2 would be carbon dioxide, not monocarbon dioxide

Due the following in your notes! Write the name for each of the following:

1. P3Cl7

1. triphosphorus heptachloride

2. S3F4

2. trisulfur tetrafluoride

3. N2Br6

3. dinitrogen hexabromide

4. N2O

4. dinitrogen monoxide

5. C3H8

5. propane

6. SF5

6. sulfur pentafluoride

Due the following in your notes! Write the formula for each of the following: 1. dihydrogen monoxide

1. H2O

2. trinitrogen pentasulfide

2. N3S5

3. carbon dioxide

3. CO2

4. tetraphosphorus decaoxide 4. P4O10

5. carbon tetrachloride

5. CCl4

6. dinitrogen monoxide

6. N2O

Empirical Formula A formula with the lowest wholenumber ratio of elements in the compound. Molecular Formula A chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound.

Write the empirical formula for the following molecular formulas. 1. C6H14

1. C3H7

2. N2O4

2. NO2

3. C4H8

3. C2H4

4. C12H18O2

4. C6H9O

5. C12H22O11

5. C12H22O11

What are the only elements that exist in nature as uncombined atoms? The noble gases. What term is used to describe such elements? Monatomic.

Which of the following gases in Earth’s atmosphere would you expect to find as molecules and which as individual atoms? a. nitrogen

b. oxygen

c. argon

d. chlorine

e. helium

f. hydrogen

Nitrogen, oxygen, chlorine, and hydrogen would be molecules. Argon and helium would be individual atoms.

Homework Write the names for the following: 1. N₂O₅ 2. P₃O₇ 3. S₃F₄ 4. CO₂ 5. N₂O₆ 6. N₂O 7. SO₃ 8. SF₆

Write the empirical formula for the following molecular formulas. 1. C₆H₁₄ 2. N₂O₄ 3. C₄H₈ 4. C₁₂H₁₈O₂ 5. N₄H₆O₄ 6. S₂O₇ 7. C₄H₃O₄ 8. C₁₂H₂₂O₁₁

Homework Write the formulas for the following compounds: 1. dihydrogen tetraoxide 2. trinitrogen pentasulfide 3. carbon dioxide 4. tetraphosphorus decaoxide 5. dinitrogen monoxide 6. carbon tetrachloride

The Nature of Covalent Bonding

Octet Rule Atoms react by gaining or losing electrons so as to acquire the stable electron structure of a noble gas. (Atoms want to look like the noble gases, they want eight outermost electrons). In order to obtain eight electrons, some atoms will share electrons with other atoms. When two atoms share two electrons (1 pair), it is called a single covalent bond.

See page 217

Unshared Electrons Electrons that are not shared are called unshared pair electrons or lone pair electrons or nonbonding electrons.

See page 218

More Covalent Bonds When two atoms share four electrons (two pairs), a double covalent bond is formed. Double bonds are stronger and shorter than single bonds.

See pages 221-222

More Covalent Bonds When two atoms share six electrons (3 pairs), a triple covalent bond is formed. Triple bonds are stronger and shorter than double bonds and single bonds.

Polyatomic Ions A polyatomic ion is a group of atoms that are covalently bonded, but has either a positive or negative charge. These ions behave as a unit.

See pages 223-225

Breaking the Bond Bond dissociation energy is the energy required to break a covalent bond. A strong bond (i.e. a triple bond) requires a large bond dissociation energy to break it.

See page 226

Resonance Sometimes a molecule can have two or more legitimate Lewis structures due to the placement of single, double or triple bonds. This is known as resonance. If more than one structure is possible, then all structures must be drawn.

See page 227

Exceptions to the Octet Rule Atoms that are happy with less than an octet: Be and B Beryllium is happy with 4 electrons (2 pairs). Boron is happy with 6 electrons (3 pairs).

See pages 228-229

Exceptions to the Octet Rule Some atoms are happy with more than an octet: P, S, I, Xe, Se, As Some are happy with 10 electrons (5 pairs), others prefer 12 electrons (6 pairs).

See pages 228-229

List 3 ways in which the octet rule can sometimes fail to be obeyed. The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number. There are also molecules in which an atom has fewer than a complete octet of valence electrons. There are also molecules in which an atom has more than a complete octet.

Which of these compounds contain elements that do not follow the octet rule? a. NF3

b. PCl2F3

c. SF4

d. SCl2

b and c do not follow the octet rule. P and S atoms have 10 valence electrons.

Bonding Theories

VSEPR Theory Valence Shell Electron Pair Repulsion theory

VSEPR Theory The repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.

The VSEPR theory plays a huge role in determining the polarity of molecules.

Chemquest 27 Molecular Shapes See pages 232-233

VSEPR Theory

Some Molecular Shapes

Use VSEPR theory to predict the shapes of the following species. a. CO2

b. SiCl4

c. SO3

d. SCl2

e. CO

f. H2Se

a. linear b. tetrahedral

c. trigonal planar

d. bent

f. bent

e. linear

Predict the shape and bond angle for the following: a. CF4

a. tetrahedral, 109.5o

b. PF3

b. trigonal pyramidal, 107o

c. F2O

c. bent, 104.5o

d. BCl3

e. SiF4

(109.5o is acceptable)

(109.5o is acceptable)

d. trigonal planar, 120o e. tetrahedral, 109.5o

Molecular Orbitals Molecular orbitals are produced when the atomic orbitals (s, p, d, f) of two atoms overlap. A molecular orbital that can be occupied by two electrons of a covalent bond is called a bonding orbital. When two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting two atomic nuclei, a sigma bond is formed.

Sigma Bonds When two s orbitals combine, a sigma bond can form…

Sigma Bonds …or when two p orbitals combine, a sigma bond can form.

Pi bonds When dealing with the p orbitals… after the sigma bond has been formed, the remaining p orbitals can form pi bonds.

Pi bonds are weaker then sigma bonds because the orbitals creating the pi bonds do not overlap as much as the orbitals creating the sigma bond.

How are atomic and molecular orbitals related? When two atoms combine, their atomic orbitals overlap to produce molecular orbitals.

Hybrid Orbitals Orbital hybridization provides information about both molecular bonding and molecular shape. In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals.

Ex. 1s ___ 2s ___ 2p ___ ___ ___ 2s and 2p orbitals mix to give sp3. sp3 ___ ___ ___ ___ 5 types of hybridization: sp3, sp2, sp, dsp3, and d2sp3

sp3 hybridization is based on the tetrahedral shape. If 4 electron regions are available around the atom, sp3 hybridization occurs.

2 H atoms

2 H atoms

1 C atom

When all 4 H atoms bond to the C atom, 4 sigma bonds form creating the methane molecule.

sp2 hybridization is based on the trigonal planar shape. If 3 electron regions are available around the atom, sp2 hybridization occurs. 2 H atoms

2 H atoms

1 C atom

When the sp2 orbitals overlap, a sigma bond forms. When the extra p orbital (in blue) overlaps,a pi bond forms. The s orbitals overlap with the outer sp2 orbitals and create sigma bonds.

1 C atom

sp hybridization is based on the linear shape. If only 2 electron regions are available around the atom, sp hybridization occurs.

Summary When determining hybridization, use Lewis structures to find the number of electron regions around the central atom(s). If 4 electron regions are available around the central atom, sp3 hybridization will occur. If 3 electron regions are available around the central atom, sp2 hybridization will occur. If 2 electron regions are available around the central atom, sp hybridization will occur.

How are atomic and molecular orbitals related? When 2 atoms combine, their atomic orbitals overlap to produce molecular orbitals. What shape would you expect a simple carbon-containing compound to have if the carbon atom has the following hybridizations? a. sp2 b. sp3 c. sp a. trigonal planar b. tetrahedral

c. linear

What types of hybrid orbitals are involved in the bonding of the carbon atoms in the following molecules? a. CH4

b. H2C=CH2

c. HC≡CH

d. N≡C-C≡N

a. sp3

b. sp2

c. sp

d. sp

Indicate the hybrid orbitals used by each carbon atom in the following compound.

sp3

sp2 sp2

sp

sp

sp3

H3C – C = C – C ≡ C – CH3 H

H

Polar Bonds and Polar Molecules

Bond Polarity Nonpolar covalent bonds are bonds where the bonding electrons are shared equally. Polar covalent bonds are bonds where the bonding electrons are not shared equally.

See pages 237-238

Electronegativity Electronegativity is the ability of an atom to attract electrons.

Electronegativity difference range

Most PROBABLE type of bond

0.0 to 0.4999 0.5 to 1.999 Greater than or equal to 2.0

Nonpolar covalent Polar covalent Ionic

Polar Bonds Partial positive (δ⁺) charges and Partial negative (δ⁻) charges δ⁺

δ⁻

H – F 2.1 4.0

δ⁺

δ⁻

S – O 2.5 3.5

Polar Bonds Dipole Moments A molecule that has two poles is called a dipolar molecule or a dipole.

H–F S–O

Polar / Nonpolar Molecules To determine the polarity of the entire molecule, two factors must be taken into account: 1. The polarity of each bond that makes up the molecule. 2. The shape of the molecule.

1. Name the shape and give the approximate bond angle. 2. Describe what type of hybridization occurs with the central atom. 3. Are the bonds polar covalent or nonpolar covalent? 4. Is the molecule polar covalent or nonpolar covalent?

Network Solids A solid substance that is entirely made up of covalently bonded atoms which build up to make a network. These are referred to as ‘giant molecules’.

Network solids typically have very high melting points (above 1000⁰C) Examples include diamond (C), silicon carbide (SiC), silica (SiO₂)

What type of bond will form between each pair of atoms – polar covalent, nonpolar covalent, or ionic? a. Na and O

a. ionic

b. P and O

b. polar

c. Ba and Cl

c. ionic

d. O and O

d. nonpolar

e. N and Br

e. polar

Draw structural formulas for each molecule and identify polar covalent bonds by assigning the partial positive and partial negative symbols to the appropriate atoms. a. NH3

b. CCl4

c. H2O

State whether the following compounds contain polar covalent, nonpolar covalent, or ionic bonds, based on their electronegativities. a. KF

a. ionic

b. SO2

b. polar covalent

c. NO2

c. polar covalent

d. Cl2

d. nonpolar covalent