General orrganic and biological chemistry structures off liffe 5th by karen timberlake06 worked examples

© 2016 Pearson Education, Inc.General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C.. © 2016 Pearson Education, Inc.General, Organic, and Biological Chemistry: Stru

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

a The element with seven protons is nitrogen In an ion of nitrogen with 10 electrons, the ionic charge would be

3–, [(7+) + (10–) = 3–] The ion, written as N3–, is the nitride ion.

b The element with 20 protons is calcium In an ion of calcium with 18 electrons, the ionic charge would be 2+,

[(20+) + (18–) = 2+] The ion, written as Ca2+, is the calcium ion.

Study Check 6.1

How many protons and electrons are in each of the following ions?

a S2– b. Al3+

Answer

a 16 protons, 18 electrons b. 13 protons, 10 electrons

a Write the symbol and name for the ion that has 7 protons and 10 electrons.

b Write the symbol and name for the ion that has 20 protons and 18 electrons.

Consider the elements aluminum and oxygen.

a Identify each as a metal or a nonmetal.

b State the number of valence electrons for each.

c State the number of electrons that must be lost or gained for each to achieve an octet.

d Write the symbol, including its ionic charge, and name for each resulting ion.

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

Lithium, which is a metal in Group 1A (1), forms Li+; nitrogen, which is a nonmetal in Group 5A (15), forms N3–

The charge of 3– is balanced by three Li+ ions

3(1+) + 1(3–) = 0

Writing the cation (positive ion) first and the anion (negative ion) second gives the formula Li3N

Study Check 6.3

Write the symbols for the ions, and the correct formula for the ionic compound that would form when calcium

and oxygen react

Group 5A (15)

Study Check 6.4

Name the compound Ga2S3

Answer

gallium sulfide

Write the name for the ionic compound Mg3N2

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

Antifouling paint contains Cu2O, which prevents the growth of barnacles and algae on the bottoms of boats What

is the name of Cu2O?

Charge Metal Ions

Step 2 Name the cation by its element name and use a Roman numeral in parentheses for the charge copper(I)

Charge Metal Ions

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

is an ionic compound

Write the correct formula for iron(III) chloride

Step 2 Balance the charges.

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

Cation Polyatomic ion (anion)

aluminum hydroxide

Al3+ OH–

is written by enclosing the formula of the hydroxide ion, OH–, in parentheses and writing the subscript 3 outside the right parenthesis

Al(OH)3

An antacid called Amphojel contains aluminum hydroxide, which treats acid indigestion and heartburn Write the

formula for aluminum hydroxide

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

nonmetal (Cl) is named chloride

is needed The subscript 3 for the Cl atoms is shown as the prefix tri The name of NCl3 is nitrogen trichloride

Name the molecular compound NCl3

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

shown as a subscript 2 in the formula The prefix tri in trioxide indicates that there are three atoms of

oxygen, shown as a subscript 3 in the formula

B2O3Write the formula for the molecular compound diboron trioxide

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

a K3P, consisting of a metal and a nonmetal, is an ionic compound As a representative element in Group 1A (1), K forms the potassium ion, K+ Phosphorus, as a representative element in Group 5A (15), forms a phosphide ion,

P3– Writing the name of the cation followed by the name of the anion gives the name potassium phosphide

b NiSO4, consisting of a cation of a transition element and a polyatomic ion SO42–, is an ionic compound As a

transition element, Ni forms more than one type of ion In this formula, the 2– charge of SO42– is balanced by one nickel ion, Ni2+ In the name, a Roman numeral written after the metal name, nickel(II), specifies the 2+ charge

The anion SO42– is a polyatomic ion named sulfate The compound is named nickel(II) sulfate

c SO3 consists of two nonmetals, which indicates that it is a molecular compound The first element S is sulfur (no

prefix is needed) The second element O, oxide, has subscript 3, which requires a prefix tri in the name The

compound is named sulfur trioxide

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

valence electrons for each of the atoms in the molecule

represented by a bond line

Draw the lewis structure for PCl3, phosphorus trichloride, used commercially to prepare insecticides and flame

retardants

Step 4 Place the remaining electrons using single or multiple bonds to complete the octets Six electrons

(3 × 2 e–) are used to bond the central P atom to three Cl atoms Twenty valence electrons are left

26 valence e– – 6 bonding e– = 20 e– remaining

We use the remaining 20 electrons as lone pairs, which are placed around theouter Cl atoms and on the

P atom, such that all the atoms have octets

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

only one Cl atom For a polyatomic ion, the atoms and electrons are placed in brackets, and the charge is written outside to the upper right

[O Cl O]–

valence electrons for each of the atoms in the ion Because the ion has a negative charge, one more electron

is added to the valence electrons

Sodium chlorite, NaClO2, is a component of mouthwashes, toothpastes, and contact lens cleaning solutions Draw

the Lewis structure for the chlorite ion, ClO2–

Step 3 Attach each bonded atom to the central atom with a pair of electrons Each bonding pair can also be

represented by a line, which indicates a single bond

to bond the O atoms to the central Cl atom, which leaves 16 valence electrons Of these, 12 electrons are drawn as lone pairs to complete the octets of the O atoms

The remaining four electrons are placed as two lone pairs on the central Cl atom

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

the carbon atom has four valence electrons, and each oxygen atom has six valence electrons, which gives a total of 16 valence electrons

O : C : O or O—C—O

atom to two O atoms, there are 12 valence electrons remaining

16 valence e– – 4 bonding e– = 12 e– remainingDraw the Lewis structure for carbon dioxide, CO2, in which the central atom is C

The 12 remaining electrons are placed as six lone pairs of electrons on the outside O atoms However, this does not complete the octet of the C atom

To obtain an octet, the C atom must share lone pairs of electrons from each of the O atoms When two bonding pairs occur between atoms, it is known as a double bond

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

a polar covalent (0.9) b nonpolar covalent (0.0) c ionic (2.6)

Using electronegativity values, classify each of the following bonds as nonpolar covalent, polar covalent, or ionic:

O—K, Cl—As, N—N, P—Br

Predict the shape of a molecule of SiCl4

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

electron-group geometry would be tetrahedral

bonded pairs and no lone pairs of electrons, the SiCl4 molecule has a tetrahedral shape

between the central N atom and O atoms, and one double bond between N and O) Note that the double bond can be drawn to any of the O atoms

electron groups would have a trigonal planar geometry

has a trigonal planar shape

Study Check 6.17

Use VSEPR theory to predict the shape of ClO2–

Answer

With two bonded atoms and two lone pairs of electrons, the shape of ClO2– is bent with a bond angle of 109°

Use VSEPR theory to predict the shape of the polyatomic ion NO3–

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

electronegativity difference of 0.5 (4.0 – 3.5 = 0.5), which makes each of the O—F bonds polar covalent

Determine whether a molecule of OF2 is polar or nonpolar

Step 2 If the bonds are polar covalent, draw the Lewis structure and determine if the dipoles cancel The Lewis

structure for OF2 has four electron groups and two bonded atoms The molecule has a bent shape in which the dipoles of the O—F bonds do not cancel The OF2 molecule would be polar

© 2016 Pearson Education, Inc.

General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

a HF is a polar molecule that interacts with other HF molecules by hydrogen bonding.

b Br2 is nonpolar; only dispersion forces provide attractive forces

c The polarity of the PCl3 molecules provides dipole–dipole attractions