chemistry-ch02_the language of chemistry

8/9/2019 Chemistry-Ch02_The Language of Chemistry

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22The languageThe language

of chemistryof chemistry


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2.1 Measurement2.1 Measurement

Measurements

always have a unit

always an associated uncertainty

Unit

specific standard quantity of a particular

property

used to measure all other quantities of

specific property


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The seven SI base units

Measurement Unit Symbol

length metre mmass kilogram kg

time second s

temperature kelvin K

amount of substance mole molelectric current ampere A

luminous intensity candela Cd


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The SI units for ANY physical quantity

can be built from the seven base units

For example area = length width

length and width are measured in metres

the unit of area is square metre, m2

Units undergo the same kinds of

mathematical operations as the

numbers to which they are attached


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SI or derived units are sometimes

inconvenient

Use prefixes that divide or multiply the

unit by a particular power of ten

Prefix Symbol Factor

kilo k 103

deci d 10-1

centi c 10-2

milli m 10-3


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Uncertainties and significant figures

Every measurement has an associated

uncertainty


24.3 C

297.45 K

24.32 C

297.47 K


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All figures up to and including the first

estimated figure are recorded

These figures are called significant figures



24.3 C

297.45 K

24.32 C

297.47 K


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Scientific notation expresses numbers in

terms of powers of ten

24.3 C is 2.43 101 C

24.32 C is 2.432 101 C



24.3 C

297.45 K

24.32 C

297.47 K


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Significant figures in calculations

Multiplication or division of

measurements

Addition or subtraction of measurements

6.

..!

v

8.1 9

2.125

3.41

247.3


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Precision

Signifies how reproducible a

measurement is when made a number of

times



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Accuracy

refers to how close the value is to the

correct value


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2.2 Representations of2.2 Representations of

moleculesmolecules

Chemical formulae

Shows the relative number of each type

of atom present in a substance

H2O

C30H34AuBClF3N O2P2PtW

A molecular formula is a chemical

formula that refers to a discrete molecule

There is a standardised way of writing

chemical formulae


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moleculesmolecules

Binary compounds

Element further to the left of the periodic

table appears first

KCl, Al2S3

Hydrogen is the exception to this rule

LiH, NH3, H2O2, HCl

If both elements are from the samegroup the lowest element appears first

SiC, BrF3


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moleculesmolecules

Binary compounds

In ionic compounds the cation is written

first followed by the anion

NaBr, MgCl2

Note: a subscripted number refers ONLY

to the atom immediately preceding it.


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moleculesmolecules

Writing chemical formulae for

compounds containing more than two

elements requires some knowledge of

the bonding within the compound.

Ionic compounds

Covalent compounds


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moleculesmolecules

Ionic compounds

Cation followed by anion

Total charge zeroCa(NO3)2(s) Ca

2+(aq) + 2NO3-(aq)

Hydrate formation common among ionic

compoundsCa(NO3)2.4H2O


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moleculesmolecules

Covalent compounds

Majority are carbon-based organic

compounds

Chemical formula often written carbon

first, followed by hydrogen and then the

remaining elements in alphabetical

order, e.g. C2H O, C4H9BrO

Limited structural information in the

chemical formula


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moleculesmolecules

Structural formulae

Attempt to show the way in which the

atoms in the molecule are bonded

together

Chemical symbols still used for each

element present

Constituent atoms are placed in theorder in which they are bonded together

Bonds between neighbouring atoms are

represented as lines


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moleculesmolecules

Structural formulae

NH3

Structural formulae do not necessarily

show the correct geometry of acompound

Presence of lone pairs of electrons is

often neglected in depictions of

molecules

NH HH

HN

H

H

NH HH


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moleculesmolecules

Organic chemistry

Structural formulae are particularly useful

Carbon atoms bond to themselves catenation

Carbon is a tetravalent element it

prefers to form a total of 4 bonds within

a molecule These bonds may be single, double or

triple


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moleculesmolecules

Structural formulae

C C

H

H

H

HC2H

ethane

C2H4

ethene

C2H2

ethyne

single bond double bond triple bond

C C

H

H

H

H

H

H

C C HH

C C C C C C


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moleculesmolecules

Structural formulae can remove

ambiguities inherent in the chemical

formula

Isomers are molecules with the same

chemical formula but different structural

formula

dimethyl etherethanolC2H OC2H O

C C O H

H

H

H

H

H C O CH

H

H

H

H

H


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moleculesmolecules

Two types of shorthand structural

formulae

condensed structural formulae

line structures

Condensed structural formulae

Constituent atoms are arranged inbonded groups, actual bonds not drawn

dimethyl ether CH3OCH3

ethanol CH3CH2OH


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moleculesmolecules

Line structures

Are constructed according to the

following guidelines:1. All bonds except C-H bonds are shown aslines.

2. C-H bonds and H atoms attached to carbon are

not shown in the line structure.

3. Single bonds are shown as 1 line; double

bonds are shown as 2 lines; triple bonds are

shown as 3 lines.

4. Carbon atoms are not labelled. All other atoms

are labelled with their elemental symbols.


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moleculesmolecules

Drawing line structures

C

C

C

H3C O

H

H

H

H

HH

C

H

H

H


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moleculesmolecules


C

C

C

H3C O

H

H

H

H

HH

C

H

H

H

C

C

C

C O C


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moleculesmolecules


C

C

C

H3C O

H

H

H

H

HH

C

H

H

H O

C

C

C

C O C


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moleculesmolecules


C

C

C

H3C O

H

H

H

H

HH

C

H

H

H

C

C

C

C O C

CH3

CH3

H3C O CH3


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moleculesmolecules


C

C

C

H3C O

H

H

H

H

HH

C

H

H

H

C

C

C

C O C

Me

Me

Me O Me


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moleculesmolecules

H

H

H

H

CH3 CH3

HH H

H

Three-dimensional structures

To draw a three-dimensional structure

add perspective to a structural formula or

line structure

cis isomer trans isomer

H

H

H

H

H CH3

HCH3 H

H


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moleculesmolecules

X

XX

X

Three-dimensional structural formulae

ML

L L

L

L

L

Tetrahedral

Conventional wayto draw 4 bonds

around a single

carbon atom

Octahedral

Transition metal ioncomplex

ML


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moleculesmolecules

X

XX

X

Three-dimensional structural formulae

Tetrahedral

Conventional wayto draw 4 bonds

around a single

carbon atom

Octahedral

Transition metal ioncomplex

ML

L

L

L

L

L

L


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2.2 Representations of2.2 Representations ofmoleculesmolecules

Three-dimensional structures


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2.3 Nomenclature2.3 Nomenclature

Nomenclature the system for

naming of compounds

International Union of Pure and AppliedChemistry (IUPAC)

Some compounds are better known by

their common unsystematic name

rather than their systematic IUPAC

name

The systematic name of water is oxidane


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1. The element closer to the left of theperiodic table appears first.

If both elements are from the same

group of the periodic table, the lower

one appears first.

Nitrogen monoxide Nitrogen dioxide Dinitrogen pentoxide


Naming Inorganic compounds

Nonmetallic binary compounds

Guidelines for naming:

NO NO2 N2O5Nitrogen monoxide Nitrogen dioxide Dinitrogen pentoxide


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2. The element that appears first retainsits elemental name.








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3. The second element begins with aroot derived from its elemental name

and ends with the suffix ide.







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4. When there is more than one atom ofa given element in the formula, the

name of the element usually contains

a prefix that specifies the number of

atoms present.








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Binary compounds of hydrogen

Hydrogen requires special consideration

It may appear first or second in the

chemical formula of a compound,

therefore first or second in the name

Lithium hydride LiH

Hydrogen fluoride HF Hydrogen sulfide H2S

Calcium hydride CaH2


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Ionic compounds

Binary ionic compounds are written with

the cation first and the anion, which

takes the suffix ide, last

Potassium iodide KI

Calcium fluoride CaF2

Ionic compounds may containpolyatomic ions

Ammonium NH4+

Nitrate NO3-


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1. The name has a root taken from the

name of the central atom

Carbonate CO32-

Nitrite NO2-


Ionic compounds

Anions containing a central atom

surrounded by oxygen atoms are known

as oxoanions. Naming rules:


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2. When an element forms 2 different

oxoanions, the one with fewer oxygen

atoms ends in ite, and the otherends in ate

Sulfite SO32-

Sulfate SO42-


Ionic compounds





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3. Chlorine, bromine and iodine each

form 4 different oxoanions that are

distinguished by prefixes and suffixes Hypobromite BrO-

Bromite BrO2-

Bromate BrO3-


Ionic compounds





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4. A polyatomic anion with a charge

more negative than 1- may add H+ to

give another anion. These anions arenamed from the parent anion by

adding the word hydrogen

Hydrogen carbonate HCO3-

Hydrogen phosphate H2PO4-


Ionic compounds





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Organic compounds

Composed primarily of carbon and

hydrogen atoms

Naming system based on the number of

carbon atoms in a particular molecule

Functional groups

A group of one or more atoms within amolecule bonded in a particular fashion

Usually the point of reaction within a

molecule


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Organic compounds

Named according to their functional

groups

Functional Name of Found

group group inhydroxyl alcohols

carbonyl aldehydes

carbonyl ketones

carboxyl carboxylic acids


R OH

C

O

R R

C

O

R OH

C

O

R H


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Alkanes

Molecules that contain only carbon and

hydrogen

Carbon atoms are joined by single bond

only

2 parts to the name of an alkane

Prefix: indicating the number of carbonatoms in the longest chain

Ending: -ane


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IUPAC rules for naming alkanes:

1. The name of an alkane with an

unbranched chain of carbon atoms

consists of a prefix showing the number ofcarbon atoms in the chain and the ending

-ane

CH3CH2CH2CH3

butane


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2. For the branched-chain alkanes, the

longest chain of carbon atoms is the

parent chain, and its name becomes theroot name

12345

2-methylpentane

CH3CH2CH2CHCH3CH3


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3. For an alkane with 1 substituent, number

the parent chain so that the carbon atom

bearing the substituent is given the lowestpossible number

2-methylpentane

12345CH3CH2CH2CHCH3

CH3


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4. Give the substituent on the parent chain a

name and number. The number shows

the carbon atom of the parent chain towhich the substituent is bonded. Use a

hyphen to connect the number to the

name

1 2 3CH3CHCH3

CH3

2-methylpropane


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5. If there are two or more identical

substituents, number the parent chain

from the end that gives the lower numberto the substituent closest to the end of the

chain

12345

2,4-dimethylhexane

CH3CH2CHCH2CH2CH3

CH3 CH3


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CH3CH2CHCH2CHCH2CH3

CH2CH3

CH31 2 3 4 5 7

3-ethyl-5-methylheptane



. If there are two or more different

substituents, list them in alphabetical

order, and number the chain from the endthat gives the lower number to the

substituent encountered first


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1 2 3 4 5

4-ethyl-2,2-dimethylhexane



7. The prefixes di, tri, tetra etc. and the

hyphenated prefixes sec- and tert- are

disregarded for the purposes of placingthe substituents in alphabetical order

CH3CCH2CHCH2CH3CH3

CH3

CH2CH3


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Constitutional isomerism in alkanes

Compounds with the same chemical

formula but a different order of

attachment of the constituent atoms

Usually distinguishable by their differing

physical properties

pentane

2,2-dimethylpropane

2-methylbutane


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General organic nomenclature The name of any compound with a chain of

carbon atoms consists of 3 parts.

1. A prefix: shows the number of carbonatoms in the parent chain

2. An infix: shows the nature of the carbon-

carbon bonds in the parent chain

3. Asuffix: shows the class of compound towhich the substance belongs, and

therefore the functional group(s) present

in the compound


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General organic nomenclature

H3CHC CH2 CH3CH2CH2CH2COH

O

propene

a carbon-carbon

double bond

a

hydrocarbon

3 carbon

atoms

pentanoic acid

only carbon-carbon

single bonds

a COOH

(carboxyl)

group

5 carbon

atoms


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