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Chapter 4 Compounds and Their Bonds

4.5Covalent Compounds

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Covalent bonds form

• when atoms share electrons to complete octets.

• between two nonmetal atoms.

• between nonmetal atoms from Groups 4A(14), 5A(15), 6A(16), and 7A(17).

Covalent Bonds

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Hydrogen Molecule

A hydrogen molecule

• is stable with two electrons (helium).

• has a shared pair of electrons.

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Forming Octets in Molecules

In a fluorine, F2,, molecule, each F atom

• shares one electron.

• attains an octet.

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Carbon forms 4 covalent bonds

In a CH4, methane, molecule

• a C atom shares 4 electrons to attain an octet.

• each H shares 1 electron to become stable like helium.

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Multiple Bonds

In nitrogen molecule, N2,

• each N atom shares 3 electrons.• each N attains an octet.• the bond is a multiple bond called a triple bond.• the name is the same as the element.

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Naming Covalent Compounds

To name covalent compounds• STEP 1: Name the first

nonmetal as an element. • STEP 2: Name the second

nonmetal with an ide ending.

• STEP 3: Use prefixes to indicate the number of atoms (subscript) of each element.

Table4.12

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What is the name of SO3?

1. The first nonmetal is S sulfur.

2. The second nonmetal is O named oxide.

3. The subscript 3 of O is shown as the prefix tri.

SO3 sulfur trioxide

The subscript 1 (for S) or mono is understood.

Naming Covalent Compounds

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Name P4S3.

1. The first nonmetal P is phosphorus. 2. The second nonmetal S is sulfide.3. The subscript 4 of P is shown as tetra. The subscript 3 of O is shown as tri.

P4S3 tetraphosphorus trisulfide

Naming Covalent Compounds

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Formulas and Names of Some Covalent Compounds

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Select the correct name for each compound.

A. SiCl4 1) silicon chloride

2) tetrasilicon chloride3) silicon tetrachloride

B. P2O5 1) phosphorus oxide

2) phosphorus pentoxide3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

2) dichlorine oxide3) chlorine heptoxide

Learning Check

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Select the correct name for each compound.

A. SiCl4 3) silicon tetrachloride

B. P2O5 3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

Solution

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Write the name of each covalent compound.

CO _____________________

CO2 _____________________

PCl3 _____________________

CCl4 _____________________

N2O _____________________

Learning Check

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Write the name of each covalent compound.

CO carbon monoxide

CO2 carbon dioxide

PCl3 phosphorus trichloride

CCl4 carbon tetrachloride

N2O dinitrogen monoxide

Solution

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The prefixes in the name are used to write the formula.

STEP 1: Write the symbols in the order of the elements in

the name.

STEP 2: Write any prefixes as subscripts.

Example: Write the formula for carbon disulfide.

STEP 1: Elements are C and S

STEP 2: No prefix for carbon means 1 C

Prefix di = 2

Formula: CS2

Guide to Writing Formulas

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Write the correct formula for each of the following.

A. phosphorus pentachloride

B. dinitrogen trioxide

C. sulfur hexafluoride

Learning Check

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Write the correct formula for each of the following.

A. phosphorus pentachloride

1 P penta = 5 Cl PCl5

B. dinitrogen trioxide

di = 2 N tri = 3 O N2O3

C. sulfur hexafluoride

1 S hexa = 6 F SF6

Solution

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Learning Check

Identify each compound as ionic or covalent and give itscorrect name.

A. SO3

B. BaCl2C. (NH4)3PO4

D. Cu2CO3

E. N2O4

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Solution

Identify each compound as ionic or covalent and give itscorrect name.

A. SO3 covalent – sulfur trioxide

B. BaCl2 ionic – barium chloride

C. (NH4)3PO3 ionic – ammonium phosphite

D. Cu2CO3 ionic – copper(I) carbonate

E. N2O4 covalent – dinitrogen tetroxide

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Learning Check

Name the following compounds.

A. Ca3(PO4)2

B. FeBr3

C. SCl2

D. Cl2O

E. N2

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Solution

Name the following compounds.

A. Ca3(PO4)2 ionic Ca2+ PO43− calcium phosphate

B. FeBr3 ionic Fe3+ Br − iron(III) bromide

C. SCl2 covalent 1S 2 Cl sulfur dichloride

D. Cl2O covalent 2 Cl 1 O dichlorine monoxide

E. N2 covalent 2N(element) nitrogen

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Learning Check

Write the formulas for the following.

A. calcium nitrate

B. boron trifluoride

C. aluminum carbonate

D. dinitrogen tetroxide

E. copper(I) phosphate

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Solution

Write the formulas for the following.

A. calcium nitrate Ca2+, NO3−

Ca(NO3)2

B. boron trifluoride 1 B, 3 F BF3

C. aluminum carbonate Al3+, CO32− Al2(CO3) 3

D. dinitrogen tetroxide 2 N, 4 O N2O4

E. copper(I) phosphate Cu+, PO43−

Cu3PO4

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Predicting Compounds using Lewis Dot Structures

Going back to the idea of Lewis dot configuration as a good way to keep track of valence electrons for predicting structure of ionic/covalent compounds.

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Ionic Compounds

Magnesium Iodide using the crossover method to determine the molecular formula and draw the structure using Lewis dot valence electrons.

Step 1: Forming the magnesium cation:

Mg2+Mg + 2e-

Step 2: Forming the iodide anion:

I + 1e- I

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Step 3: Putting the ions together

We need 2 iodide anions to balance the +2 charge on the magnesium, as indicated by the formula MgI2

IMg2+I

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Covalent Compounds

Covalent compounds between oxygen and hydrogen

Step 1: Determine how many bonds are formed by oxygen

Step 2: Determine how many hydrogen atoms are in the chemical formula (hydrogen forms a single bond)

Step 3: Draw the structure

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Draw the structure for H2O

O6 valence e- 2 max bonds

O H

H

O H2

6 valence e-

and

1 valence e-H2O

H1 valence e- 1 bond each

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Covalent Compounds

Covalent compounds between carbon and hydrogen

Step 1: Determine how many bonds are formed by carbon

Step 2: Determine how many hydrogen atoms are in the chemical formula (hydrogen forms a single bond)

Step 3: Draw the structure

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Draw the structure for CH4

H1 valence e- 1 bond each

4 valence e- 4 max bondsC

H4

4 valence e-

and

1 valence e-

CH4

C H

H

C

H

H