chemistry stpm matter chapter 1

7/27/2019 Chemistry STPM Matter Chapter 1

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Chapter 1 : MATTER

1.1 Atoms and Molecules1.2 Mole Concept


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1.1 Atoms and Molecules


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MATTER1.1 ATOMS

&

MOLECULE

Subatomic particles

Proton no, nucleon no

Isotope , isotope notation

Ar, Mr

Mass spectrometer

Analyze mass spectrum

Calculate average atomic massCations,anions,salts


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Learning OutcomeAt the end of this lecture, students should be able :

(a) Identify and describe proton, electron andneutron as subatomic particle.

(b) Define proton number, Z, nucleon number, A

and isotope. Write isotope notation.

(c) Define relative atomic mass, Arand

relative molecular mass, Mrbased on

the C-12 scale.


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Introduction

Matter

Anything that occupies space and has mass.

e.gair, water, animals, trees, atoms, ..

Matter may consists of atoms, molecules or ions.


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Three States of Matter

SOLID LIQUID GAS


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1.1.1 Atoms

An atom is the smallest unit of a chemical

element/compound. In an atom, there are three subatomic particles:

- Proton (p)

- Neutron (n)

- Electron (e)

1.1 Atoms and Molecules

Packed in a small nucleus

Move rapidly around the nucleus of an atom


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Modern Model of the Atom

Electrons move around the region of the atom.

(The nucleus is surrounded by a cloud of electrons

Electrons cloud


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Fundamental Particles of Atoms

The particles in a nucleus are called

nucleons which made up of protons and

neutrons.

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Subatomic ParticlesParticle Symbol Charge

(units)

Relative

mass

(a.m.u)

Approximate

relative

mass

(units)

Proton(p)

1 1 p +1 1.007 1.0

Neutron

(n)

10n 0

1.0091.0

Electron

(e)

0-1 e -1 0.000543

(1/1840)

0


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Effect of Electric and

Magnetic Fields on

Subatomic Particles

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The behaviour of a beam of protons,neutrons and

electrons in an electric field

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The NEGATIVE electrons are deflected to

the positive plate.

The neutrons, which do not carry any

electrical charge, are not deflected.

The POSITIVE protons are deflected to

the negative plate.

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The behaviour of a beam of protons,neutrons and

electrons in a magnetic field

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The beams of electrons is deflected much

more the the beam of protons in the

electric or magnetic field.

This shows the electrons are lighter than

protons


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STPM 2003/P2/Q1


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Elements

A substance that cannot be separated into

simpler substances by chemical reactions.

example: Na , Al, C, Ne

An element is composed of atoms of only

one kind.example: oxygen gas, florine gas


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Isotope

Isotopes are two ormore atoms of the same

element that have the same number of

protons in their nucleus but different number

of neutrons. Examples:

Hg20080

Hg20080

(D)21H

U23592 U238

92

(T)H31H1

1


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Isotopes have the same chemical

properties because they are atoms of the

same element and different physical

properties.

These physical properties include

melting point,boiling point,density and

rate of of diffusion.

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Stable and Unstable isotopes

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Isotope Notation

X = element symbol

Z = Proton Number

of X

= p

A = Nucleon Numberof X

= Z + n

An atom can be represented by an isotope notation

( atomic symbol )


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Total charge on

the ion

Number of

atoms that

formed the ionprotonnumber of

mercury,

Z = 80

Nucleon number of

mercury, A = 202

The number of

neutrons

= A Z

= 202 80

= 122


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Exercise 1

Symbol Number of : Charge

Proton Neutron Electron

Give the number of protons, neutrons,electrons

and charge in each of the following species:

Hg20080

Cu6329217

8O

35927Co


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Exercise 1(answer)

Symbol Number of : Charge

Proton Neutron Electron

80 120 80 0

29 34 29 0

8 9 10 2-

27 32 24 3+

Give the number of protons, neutrons,electrons

and charge in each of the following species:

Hg20080

Cu6329217

8O

35927Co


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Exercise 2

Species Number of : Notation

for

nuclideProton Neutron Electron

A 2 2 2

B 1 2 0

C 1 1 1

D 7 7 10

Write the appropriate notation for each of the

following nuclide :


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Exercise 2(answer)

Species Number of : Notation

for

nuclideProton Neutron Electron

A 2 2 2

B 1 2 0

C 1 1 1

D 7 7 10

Write the appropriate notation for each of the

following nuclide :


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Special case ;

14

7 N

14

6 C +0

+1e (Positron Emission)

Exercises;

Write equations for the following radioactivedecay reactions.Identify X and Y.

(a) 146 C X ( decay)

(b) 23994 Pu Y ( decay)

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1.1.5 Ion

Cation

a positive charge ion

formed when a neutral atomloses an electron(s).

11 protons 11 protons

11 electrons 10 electrons

Two types of ions : a) cation b) anion

Na Na+

Anion

a negative charge ion

formed when a neutral atomgains an electron(s).

17 protons 17 protons

17 electrons 18 electrons

Cl Cl-


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STPM 2003/P2/Q1(b)

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Molecule A molecule consists of a small number of atoms

joined together by bonds.


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A diatomic molecule

Contains only two atoms

Example :

H2, N2, O2, Br2, HCl, CO

A polyatomic molecule

Contains more than two atoms

Example :

O3, H2O, NH3, CH4


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A plot of the number ofneutrons,N, against the number of

protons,P, for all non-reactivenuclei fall in a well defined belt or

band in (figure 1.3)

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Relative Isotopic Mass

i. Relative Isotopic MassA mass of one atom of the isotopecompared to 1/12 mass of one atom of12Cwith the mass 12.000

C

lative

12ofatomoneofMassX121

isotopetheofatomoneofMass

mass,IsotopicRe


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Isotope Relative Isotopic Mass NucleonNumber


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Relative Mass

ii. Relative Atomic Mass, ArA mass of one atom of an elementcompared to 1/12 mass of one atom of12Cwith the mass 12.000

C

lative

12ofatomoneofMassX121

elementofatomoneofMass

Armass,atomicRe


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Example 1 Determine the relative atomic mass of an

element Y if the ratio of the atomic mass of Y to

carbon-12 atom is 0.45ANSWER:

Ar (Y) : Ar (Carbon-12)= 0.45 : 1

Ar (Y) =0.45 x Ar (carbon-12)

= 0.45 x 12

= 5.4

1

45.0

)12(

)(

carbonAr

YAr

iii) Relative Molecular Mass, Mr


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) , A massof one molecule of a compound

compared to 1/12 mass of one atom of12Cwith the mass 12.000

C12ofatomoneofMassX

12

1

compoundaofmoleculeoneofMass

Mrmass,molecularRelative

The relative molecular mass of a compound is

the summation of the relative atomic masses

of all atoms in a molecular formula.

Example 2


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Example 2 Calculate the relative molecular mass of

C5H5N,

Ar C = 12.01

Ar H = 1.01

Ar N = 14.01

ANSWER:

Mr = 5(Ar of C) + 5(Ar of H) + Ar of N

= 5(12.01) + 5(1.01) + 14.01

= 60.05 + 5.05 + 14.01

= 79.11


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For elements that have isotopes,

the relative atomic mass is

calculated by using the formula:

Relative atomic mass, (Ar)= m1X + m2y + m3z

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Where,

m1, m2, m3 = nucleon numbers of isotopes

1,2 and 3 respectively.

x,y,z = relative abundance of isotopes

1,2 and 3 respectively.

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Calculate the relative atomic mass of

naturally occurring silicon from the

following data.

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Isotopes Relative

abundanceSilicon-28 92.21%

Silicon-29 4.7%

Silicon-30 3.09%


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Relative atomic mass, (Ar) of Silicon,

= (28 x 92.21) +(29 x 4.7) + (30 x 3.09)

100

= 28.1

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Many compounds do not exist as molecules.

When considering ionic compounds such assodium chloride,Na+Cl- , the term RFM issued

in place of RMM.

Sodium Chloride- made up of positive and

negative ions and not

molecules

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The mass of an ion is very close

to the mass of its atom.

Hence, the RAM of the atoms are

used to calculate the RFM.

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STPM 2006/P1/Q1


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STPM 2006/P1/Q1


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Learning Outcome

At the end of this lecture, students should

be able :

(a) Sketch and explain the following main

components of a simple mass

spectrometer.


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Mass Spectrometer

A mass spectrometer is used todetermine:

i. Relative atomic mass of an element

ii. Relative molecular mass of acompound

iii. Types of isotopes, the abundance

and its relative isotopic massiv. Recognize the structure of thecompound in an unknown sample

A Mass Spectrometer


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+

AMPLIFIER

- -

AccelarationChamber

Vacuum

Pump

Heated

Filament

Vaporisation

Chamber

Ionisation

Chamber

Magnetic

Chamber

Ion Detector

Recorder

A Mass Spectrometer

Ion Beam


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Vaporisation Chamber

- sample of the element is vaporised into

gaseous atom

Ionisation Chamber


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Ionisation Chamber- A gaseous sample is bombarded by astream of high-energy electrons that are

emitted from a hot filament.

- Collisions between the electrons and

the gaseous sample produce positive ions

Acceleration Chamber


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Acceleration Chamber

- the positive ions are acceleratedby

an electric field towards the twooppositely charge plates

- the electric field is produced by a

high voltage between the two plates

- the emerging ions are ofhigh and

constant velocity.


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Vacuum Pump

A pump maintains a vacuum inside the

mass spectrometer to avoid any small

particle that would block the movement.


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Magnetic Field

- The positive ions are separated and

deflected into a circular path by a magnet

according to its mass / charge (m/e)

ratio.

- Positive ions with small m/e ratioare

deflected most .Ions with large m/e ratioare deflected least.


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Beam of35Cl+ and 37Cl+

35Cl+ 37Cl+

Ion Detector


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Ion Detector

The numbers of ions and types of

isotopes are recorded as a massspectrum.

Example : A mass spectrum of Mg

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8.1 9.1

24 25 26

Relative

abundanc

e

m/e (amu)

Mass Spectrum of Magnesium


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Mass Spectrum of Magnesium The mass spectrum of Mg

shows that Mg consists of

three isotopes: 24Mg,25Mg and 26Mg.

The height of each lineispropartional to the

abundance of each

isotope.

24Mg is the most abundant

of the three isotopes

63

8.19.1

24 25 26

Relative

abundance

m/e (amu)


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Fi 1 4 d 1 5 h th f


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Figure 1.4 and 1.5 shows the passages of

16O+ , 17O+ , 18O+ and 18O2+ through a

magnetic field.

Identify the particles A,B,C and D

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Learning Outcome


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g

At the end of this lecture, students shouldbe able :

(a) Analyse mass spectrum of an element.

Calculate the average atomic mass of

an element given the relativeabundance of isotopes or a mass

spectrum.

(b) Name cation, anions and salt according

to the IUPAC nomenclature.

How to calculate the relative atomic


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How to calculate the relative atomic

mass from mass spectrum?

i

ii

Q

MQAr

Q = therelative abundance / percentage

abundance of an isotope of the element

M = the relative isotopic mass of the element

Example 1


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Example 11. Fig 1.1 shows the mass spectrum

of the element rubidium, Rb;

a. What isotopes are present inRb?

b. What is the percentageabundance of each isotope?

18

7

85 87

Relativeabund

ance

m/e

(amu)

85Rb and 87Rb

% abundance

85

Rb= 18 x 100

25

= 72 %

% abundance 87Rb

= 7 x 100

25

= 28 %

Example 1 (cont)


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Example 1 (cont)c. Calculate the relative atomic mass of Rb.

85.56

amux12.00121

amu85.56RbofA

amu85.56

25

)87x7()85x18(

QiRbofmassAverage

r

QiMi


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Example 2

6.94?isLiofmassatomicrelativetheif

isotopeeachofabundancepercentagetheisWhat

.7.02and6.01are73and6

3

ofmassatomicrelativeTheLiLi

Assume that,% b d f 6Li X %


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% abundance of6Li = X %

% abundance of7Li = (100 - x) %

Ar Li = QiMi

Qi

6.94 = X (6.01) + (100 X) 7.02

X + 100 X6.94 = 6.01 X + 702 7.02 X

100

694 - 702 = -1.01 X

+8 = +1.01 XX = 7.92 %

So, % abundance of6Li = 7.92 %

And % abundance of7Li = 92.08 %


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I i Ab d


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Isotopic Abundance

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Interpreting Mass Spectra

in Terms of RelativeAbundance of Isotopes

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Interpreting Mass Spectra in

Terms of Molecular fragments

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Th t f M th


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The mass spectrum of Methane

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Th t f Eth l


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The mass spectrum of Ethanol

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Solution :


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Solution :

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Solution;


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Solution;

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IUPAC Nomenclature of Ions


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A) Cations

i) For the metals of group 1, 2 and 13 :

Name the metals followed by the word ions

e.g : Na+ : sodium ion, Al3+ : aluminium ion

ii) For the metal with more oxidation states,

Roman numerals are used to indicate the

oxidation state.

e.g : Cu2+ : copper(II) ion, Fe3+ : iron(III) ion

B. Anions


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Monoatomic ions have names that ended with

idee.g : F- : fluoride ion, O2- : oxide ion

Other polyatomic anions have their own names

e.g : CO32- : carbonate ion,

SO42- : sulphate ion,

Cr2O72- : dichromate ion

When a metal combines with a non-metal


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When a metal combines with a non-metal

element, the metal is named before the

nonmetal

Example : Fe2(SO4)3 - Iron(III) sulphate

FeCl3 - Iron(III) chloride

CuCl2

- copper(II) chloride

chemistry stpm matter chapter 1

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