Chapter 2 Molecules & Ions & Compounds

7/30/2019 Chapter 2 Molecules & Ions & Compounds

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Copyright (c) 1999 by Harcourt Brace & Company

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Molecules, Ions &Their Compounds

NaCl, salt

Buckyball, C60

Ethanol, C2H6O
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Compounds & Molecules

COMPOUNDSare a combination of 2 ormore elements in definite ratios by mass.

The character of each element is lost when

forming a compound.

MOLECULESare the smallest unit of acompound that retains the characteristics of

the compound.


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MOLECULAR FORMULAS

Formula for glycine is C2H5NO2 In one molecule there are

2 C atoms

5 H atoms

1 N atom

2 O atoms


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WRITING FORMULAS

Can also write glycine formula as

H2NCH2COOH

to show atom ordering

or in the form of a structural formula

C

H

H C

H

H

O

O HN


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MOLECULAR MODELING

C

H

H C

H

H

O

O HN

Ball & stick Space-filling

Structural formula

of glycine


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Molecular & Ionic Compounds

Heme NaCl

Fe

N


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ELEMENTS THAT EXIST AS

MOLECULES

Allotropes of C


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ELEMENTS THAT EXIST ASDIATOMIC MOLECULES


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ELEMENTS THAT EXIST ASPOLYATOMIC MOLECULES

White P4 and polymeric

red phosphorus

S8 sulfurmolecules


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IONS AND IONIC COMPOUNDS

see Screen 3.5

IONSare atoms or groups of atoms with apositive or negative charge.

Taking away an electron from an atom gives a

CATION with a positive charge

Adding an electron to an atom gives an

ANION with a negative charge.


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Forming Cations & Anions

A CATION forms

when an atom

loses one or

more electrons.

An ANION forms

when an atom

gains one or

more electrons

Mg --> Mg2+ + 2 e- F + e- --> F-
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Active figure 3.5


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PREDICTING ION CHARGES

In general

metals (Mg) lose electrons ---> cations

nonmetals (F) gain electrons ---> anions

See CD-ROM Screen 3.5 and book Figure 3.7


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Charges on Common Ions

+3

-4 -1-2-3+1

+2

By losing or gaining e-, atom has same

number of e-s as nearest Group 8A atom.


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Predicting Charges on Monatomic Ions


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METALS

M ---> n e- + Mn+where n = periodic group

Na+ sodium ion

Mg2+ magnesium ion

Al3+ aluminum ion

Transition metals --> M2+ or M3+are common

Fe2+ iron(II) ion

Fe3+ iron(III) ion


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NONMETALS

NONMETAL + n e- ------> Xn-where n = 8 - Group no.

C4-,carbide N3-, nitride O2-, oxide

S2-, sulfide

F-, fluoride

Cl-, chloride

Group 7AGroup 6AGroup 4A Group 5A

Br-, bromide

I-, iodide

Name derivedby adding -ideto stem


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Valence Electrons

3Li

7

4Be

9.4

9F

19

5B

11

7N

14

6C

12

8O

16

Li BBe C N O F

10Ne

19Ne

The Octet Rules

Lewis

electron dot

diagrams


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Sodium can loose one electron to expose

an octet

Chlorine can gain one electron to

complete an octet

11Na

23Na

17Cl

35.5Cl

[Na]+

+

Cl

+

-

V l


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Valence Atoms differ in their combining

power or valence.

Na combines with one Cl, NaCl, whileCa combines with two, CaCl2

We say that Ca has a valence of twoand sodium a valence of one whencompared to Cl.

Cl, a non metal is given a valence of

1-, in contrast to Na which is 1+or Ca= 2+.

Sulfur has a valence of 2- so it forms

Na2S.


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Valence and Charge

Atoms with positive valence formpositive ions by loosing electrons.

Atoms with negative valence form

negative ions by gaining electrons. The charge of an ion is determined

by the difference between the

number of protons and the numberof electrons.


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Ionic charge from theperiodic table


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Ionic Compounds

The atoms of ionic compounds existas charged ions and are heldtogether by strong electrostaticforces creating a crystal lattice.

NaCl, FeCl2, NaHCO3, (NH4)2SO4

Water molecules are sometimesincorporated into the lattice creatingcompounds called hydrates.

CuSO45H2O


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Ionic Compounds Electrostatic forces attraction

and repulsion by two chargedspecies

The force of attraction betweentwo oppositely charged ions isgreater as their charges increaseand the distance (d) decreases

Generally arranged in a crystallattice network

M t l i C ti


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Metal ions- CationsCations are named with the name of the element.

Na+ -sodium

H+ - hydrogen

K+ -potassium

Ca2+ - calcium

Some Cations have common names and may exist with

several different ionic charges; these are denoted with Romannumerals showing the amount of positive charge on the ion.

Fe2+ Iron(II) Ferrous ion

Fe3+ Iron(III) Ferric ion

Cu2+ Copper(II) Cupric ion

Cu1+ Copper(I) Cuprous ion

Lead(II), (IV), Mercury(I), (II), Tin(III), (IV) are only some of

the other metals forming multiple ions


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Negative Ions - AnionsAnions are named by changing the ending of the element

name to ide.

Cl1- Chloride

O2- Oxide

H1- Hydride

N3- Nitride


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POLYATOMIC IONSCD Screen 3.6

Groups of atoms with a charge.

MEMORIZE the names and

formulas in Table 3.1, page 107.


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Note: many Ocontaining anions

have names ending

inate (or -ite).


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CATION +

ANION --->COMPOUND

A neutral compd.

requires

equal number of +

and - charges.

COMPOUNDSFORMED FROM

IONS

Na+ + Cl- --> NaCl


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Some Ionic Compounds

Mg2+ + NO3- ---->

Mg(NO3)2

magnesiumnitrate

Fe2+ + PO43- ---->

Fe3(PO4)2

iron(II) phosphate(See CD, Screen 3.11 for naming

practice)

calcium fluoride

Ca2+

+ 2 F-

---> CaF2

roperties o Ionic


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roperties o IonicCompounds

Forming NaCl from Na and Cl2

A metal atom cantransfer anelectron to a

nonmetal. The resulting

cation and anionare attracted to

each other byelectrostaticforces.
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Copyright (c) 1999 by Harcourt Brace & CompanyAll rights reserved

Electrostatic Forces

The oppositely charged ions in ionic compounds are

attracted to one another by ELECTROSTATIC

FORCES.These forces are governed by COULOMBS LAW.
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COULOMBS LAW

As ion charge increases, the attractive force

_______________.

As the distance between ions increases, theattractive force ________________.

This idea is important and will come upmany times in future discussions!


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COULOMBS LAW

Active Figure 3.10


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Importance of Coulombs Law

NaCl, Na+ and Cl-,

m.p. 804 oCMgO, Mg2+ and O2-

m.p. 2800 oC

Naming Ionic


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Naming IonicCompounds

Positive ion name goes firstfollowed by the negative ion

CaBr2

Mg(OH)2

KCl

AgSO4 NH4CO3

Molecular


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MolecularCompounds

Binary compounds:

use valence to write formulas as if theywere ionic.

use prefixes: mono-1, di-2, tri-3,tetra-4,

penta-4, hexa-6.for both anion andcation.


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Molecular CompoundsCompounds without Ions

CH4 methane

CO2 Carbon dioxide

BCl3 boron trichloride


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Naming MolecularCompounds

CH4 methaneBCl3

boron trichloride

CO2 Carbon dioxide

All are

formed from

two or more

nonmetals.

Ionic

compounds

generallyinvolve a metal

and nonmetal

(NaCl)

Naming Binary


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Naming BinaryCompounds

Usually put the the elements inincreasing atomic number

Use prefixes such as di-, tri-, etc

There are some common namesthat are still used for somecompounds (see page 96)

Example: water, ammonia,methane

N i Bi


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Naming BinaryCompounds

NF3

Nitrogen trifluoride

N2O4

Dinitrogen tetraoxide

SF6

Sulfur hexafluoride

NO2

Dinitrogen dioxide

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Chapter 2 Molecules & Ions & Compounds