Chapter 4 Forces Between Particles 4.6

Covalent Compounds

Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings

1

Covalent Bonds 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).

2

Hydrogen Molecule

A hydrogen molecule • is stable with two electrons (helium).

• has a shared pair of electrons.

3

Forming Octets in Molecules

In a fluorine, F 2 , , molecule, each F atom • shares one electron.

• attains an octet.

4

Carbon forms 4 covalent bonds

In a CH 4 , methane, molecule • a C atom shares 4 electrons to attain an octet.

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

5

Multiple Bonds

• • • • In nitrogen molecule, N 2 , 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.

6

Naming Covalent Compounds

• • • To name covalent compounds

Table4.12

STEP 1:

Name the first nonmetal as an element.

STEP 2:

Name the second nonmetal with an

ide

ending.

STEP 3:

Use

prefixes

indicate the number of to atoms (subscript) of each element.

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Naming Covalent Compounds

What is the name of SO 3 ?

1. The first nonmetal is S sulfur. 2. The second nonmetal is O named ox

ide.

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

tri

.

SO 3  sulfur

tri

oxide The subscript 1 (for S) or

mono

is understood.

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Naming Covalent Compounds

Name P 4 S 3 .

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

.

P 4 S 3 

tetra

phosphorus

tri

sulfide

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Formulas and Names of Some Covalent Compounds

Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings

10

Learning Check

Select the correct name for each compound.

A.

SiCl B. P C.

Cl 2 2 O O 4 5 7 1) silicon chloride 2) tetrasilicon chloride 3) silicon tetrachloride 1) phosphorus oxide 2) phosphorus pentaoxide 3) diphosphorus pentaoxide 1) dichlorine heptaoxide 2) dichlorine oxide 3) chlorine heptaoxide

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Solution

Select the correct name for each compound.

A.

SiCl 4 B. P 2 O 5 C.

Cl 2 O 7 3) silicon tetrachloride 3) diphosphorus pentaoxide 1) dichlorine heptaoxide

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Learning Check

Write the name of each covalent compound.

CO CO 2 PCl 3 CCl 4 N 2 O _____________________ _____________________ _____________________ _____________________ _____________________

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Solution

Write the name of each covalent compound.

CO CO 2 PCl 3 CCl 4 N 2 O carbon monoxide carbon dioxide phosphorus trichloride carbon tetrachloride dinitrogen monoxide

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Guide to Writing Formulas

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: CS 2

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Learning Check

Write the correct formula for each of the following.

A. phosphorus pentachloride B. dinitrogen trioxide C. sulfur hexafluoride

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Solution

Write the correct formula for each of the following.

A. phosphorus pentachloride 1 P penta = 5 Cl PCl 5 B. dinitrogen trioxide di = 2 N tri = 3 O N 2 O 3 C. sulfur hexafluoride 1 S hexa = 6 F SF 6

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Learning Check

Identify each compound as ionic or covalent and give its correct name.

A. SO 3 B. BaCl 2 C. (NH 4 ) 3 PO 4 D. Cu 2 CO 3 E. N 2 O 4

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Solution

Identify each compound as ionic or covalent and give its correct name.

A. SO 3 B. BaCl 2 C. (NH 4 ) 3 PO 3 D. Cu 2 CO 3 E. N 2 O 4 covalent – sulfur trioxide ionic – barium chloride ionic – ammonium phosphite ionic – copper(I) carbonate covalent – dinitrogen tetroxide

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Learning Check

Name the following compounds.

A. Ca 3 (PO 4 ) 2 B. FeBr 3 C. SCl 2 D. Cl 2 O E. N 2

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Solution

Name the following compounds.

A. Ca 3 (PO B. FeBr 3 4 ) 2 ionic ionic Ca Fe 2+ 3+ PO 4 3 − Br − calcium phosphate iron(III) bromide C. SCl 2 covalent 1S 2 Cl sulfur dichloride D. Cl 2 O covalent 2 Cl 1 O dichlorine monoxide E. N 2 covalent 2N(element) nitrogen

21

Learning Check

Write the formulas for the following.

A. calcium nitrate B. boron trifluoride C. aluminum carbonate D. dinitrogen tetroxide E. copper(I) phosphate

22

Solution

Write the formulas for the following.

A. calcium nitrate Ca 2+ , NO 3 − B. boron trifluoride 1 B, 3 F C. aluminum carbonate Al 3+ , CO 3 2 − D. dinitrogen tetroxide 2 N, 4 O E. copper(I) phosphate Cu + , PO 4 3− Ca(NO 3 ) 2 BF 3 Al 2 (CO 3 ) 3 N 2 O 4 Cu 3 PO 4

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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:

Mg Mg 2+ + 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 MgI 2 I Mg 2+ 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 27

Draw the structure for H

2

O

6 valence e O 2 max bonds 1 valence e H 1 bond each O and 2 H 6 valence e 1 valence e H O H 2 O H

28

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 29

Draw the structure for CH

4 4 valence e C 4 max bonds 1 valence e H C and 4 H 4 valence e 1 valence e H 1 bond each H C H H CH 4

30