new way chemistry for hong kong a-level book 11 atomic structure and relative masses 1.1the atomic...

New Way Chemistry for Hong Kong A-Level Book 11

Atomic Structure Atomic Structure and Relative Massesand Relative Masses

1.11.1 The Atomic Nature of MatterThe Atomic Nature of Matter

1.21.2 The Experimental Evidence of Atomic StructureThe Experimental Evidence of Atomic Structure

1.31.3 Sub-atomic ParticlesSub-atomic Particles

1.41.4 Atomic Number, Mass Number and IsotopesAtomic Number, Mass Number and Isotopes

1.51.5 Mass SpectrometerMass Spectrometer

1.61.6 Relative Isotopic, Atomic and Molecular MassesRelative Isotopic, Atomic and Molecular Masses

11


1.1.11 The Atomic The Atomic

Nature of Nature of MatterMatter


What is “atom”?What is “atom”?

1.1 The atomic nature of matter (SB p.2)

The Greek philosopher Democritus


Iron

Continuous division

Continuous division


These are iron atoms!!


Dalton’s atomic Dalton’s atomic theorytheoryJohn Dalton proposed his Dalton’s atomic theory



Main points of Dalton’s atomic Main points of Dalton’s atomic theorytheory


5. Atoms of different elements combine to form a compound. The numbers of various atoms combined bear a simple whole number ratio to each other.

1. All elements are made up of atoms.

2. Atoms can neither be created nor destroyed.

3. Atoms of the same element are identical. They have the same mass and chemical properties.

4. Atoms of different elements are different. They have different masses and chemical properties.

Check Point 1-1Check Point 1-1


The The Experimental Experimental Evidence of Evidence of

Atomic Atomic StructureStructure

1.1.22


1.2 The experimental evidence of atomic structure (SB p.3)

Discovery of electronsDiscovery of electrons

• A beam of rays came out from the cathode and hit the anode

• He called the beam cathode rays



The beam was composed of negatively charged fast-moving particles.Deflected in

the electric field

Deflected in the magnetic

field



Measure the mass to charge ratio (m/e) of the particles produced Independent of the

nature of the gas inside the discharge tube

The particles were constituents of all atoms!!

He called the particles ‘electrons’.



Thomson’s atomic Thomson’s atomic modelmodel

Atom

An atom is electrically neutral

No. of positively charged particles

=

No. of negatively charged particles



How are the particles distributed How are the particles distributed in an atom?in an atom?

+ +

+

+ +

+

Positive charge

• An atom was a positively charged sphere

• Negatively charged electrons embedded in it like a ‘raisin pudding’

Electron



Gold foil scattering experimentGold foil scattering experiment

• performed by Ernest Rutherford



• He bombarded a thin gold foil with a beam of fast-moving -particles (+ve charged)

Observation:

• most -particles passed through the foil without deflection

• very few -particles were scattered or rebounded back



Interpretation of the experimental resultsInterpretation of the experimental results

• The condensed core is called ‘nucleus’

• The positively charged particle is called ‘proton’



Rutherford’s atomic Rutherford’s atomic modelmodel

Expectation:

Mass of atom = Total mass of protons

Mass of atom > Total mass of

protons



Chadwick’s atomic modelChadwick’s atomic model

• presence of neutrons

• proved by James Chadwick


Chadwick’s atomic Chadwick’s atomic modelmodel


ProtonElectron

Neutron Check Point 1-2Check Point 1-2


Sub-atomic Sub-atomic ParticlesParticles

1.1.33


Sub-atomic particlesSub-atomic particles

1.3 Sub-atomic particles (SB p.6)

3 kinds of sub-atomic particles:

• Protons

• Neutrons

• Electrons

Inside the condensed nucleus

Moving around the nucleus


A carbon-12 atomA carbon-12 atom



Characteristics of sub-atomic Characteristics of sub-atomic particlesparticles


Sub-atomic particle

Proton Neutron Electron

Symbol p or n or e- or

Location in atom

Nucleus Nucleus Surrounding the nucleus

Actual charge (C)

1.6 10-9 0 1.6 x 10-9

Relative charge +1 0 -1

Actual mass (g) 1.7 10-24 1.7 10-24 9.1 10-28

Approximate relative mass (a.m.u.)

1 1 0

H11

n10

e0-1


Relative size of the atom and the Relative size of the atom and the nucleusnucleus




Atomic Atomic Number, Number,

Mass Mass Number and Number and

IsotopesIsotopes

1.1.44


Atomic numberAtomic number1.4 Atomic number, mass number and isotopes (SB p.7)

The atomic number (Z) of an element is the number of protons contained in the nucleus of the atom.

Atomic number =

Number of protons

Number of electrons=

Reason: Atoms are electrically neutral.

WHY?


Mass numberMass number

1.4 Atomic number, mass number and isotopes (SB p.8)

The mass number (A) of an atom is the sum of the number of protons and neutrons in the nucleus.

Mass number

=Number of

protonsNumber of neutrons

+


Atomic numbers and mass Atomic numbers and mass numbers numbers of some common atomsof some common atoms


Atom No. of protons

No. of electrons

No. of neutrons

Atomic number

Mass number

Hydrogen 1 1 0 1 (1 + 0) = 1

Oxygen 8 8 8 8 (8 + 8) = 16

Argon 18 18 22 18 (18+22) = 40


IsotopesIsotopes1.4 Atomic number, mass number and isotopes (SB p.8)

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

Representation:

XA

Z

Symbol of the elementMass

number

Atomic number



e.g. the two isotopes of chlorine are written as:

Cl3517 Cl

3717

OR labelled as Cl-35 and Cl-37.




Element Isotope Atomic number

No. of protons

No. of neutrons

Natural abundanc

e (%)

Hydrogen 1 1 0 99.8

1 1 1 0.02

Carbon 6 6 6 98.89

6 6 7 1.11

6 6 8 trace

Isotopes of some common Isotopes of some common elementselements

H11

H21

C12

6

C13

6

C14

6


Mass Mass SpectrometeSpectromete

rr

1.1.55


1.5 Mass spectrometer (SB p.10)

Mass spectrometerMass spectrometer

A highly accurate instrument!


Mass spectrometer consists of 6 Mass spectrometer consists of 6 parts:parts:



Mass spectrum of Mass spectrum of ClCl22::


m/e ratio Corresponding ion

35 35Cl+

37 37Cl+

70 35Cl─35Cl+

72 35Cl ─ 37Cl+

74 37Cl ─37Cl+


Mass spectrum of CHMass spectrum of CH33Cl:Cl:

m/e ratio Corresponding ion

35 35Cl+

37 37Cl+

50 12CH3─35Cl+

51 13CH3 ─ 37Cl+

52 12CH3 ─37Cl+




Relative Relative Isotopic, Isotopic,

Atomic and Atomic and Molecular Molecular MassesMasses

1.1.66


1.9 Relative isotopic, atomic and molecular masses (SB p.22)

Relative isotopic massRelative isotopic mass

The relative isotopic mass of a particular isotope of an element is the relative mass of one atom of that isotope on the carbon-12 scale.

e.g. relative isotopic mass of Cl-35 = 35

relative isotopic mass of Cl-37 = 37



What is carbon-12 scale?What is carbon-12 scale?

Mg has the same mass as two C-12 atoms

use carbon-12 as the reference standard


Relative atomic massRelative atomic mass

The relative atomic mass of an element is the weighted average of the relative isotopic masses of its natural isotopes on the carbon-12 scale.




What is the relative atomic mass of Cl?What is the relative atomic mass of Cl?The relative abundances of Cl-35 and Cl-37 are 75.77 a

nd 24.23 respectively

Relative atomic mass of Cl

=

= 35.48

24.23)(75.5524.23)(3775.77)(35


Relative molecular Relative molecular massmass


The relative molecular mass is the relative mass of a molecule on the carbon-12 scale.



What is the relative molecular mass of CH3Cl?

Relative molecular mass of CH3Cl

=

= 50.5040)2(123

40)(522)(51123)(50

Example 1-6Example 1-6



The END


(a)What does the word “atom” literally mean?

(b)Which point of Dalton’s atomic theory is based on the law of conservation of mass proposed by Lavoisier in 1774 which states that matter is neither created nor destroyed in the course of a chemical reaction?

(c)Which point of Dalton’s atomic theory is based on the law of constant proportion proposed by Proust in 1799 which states that all pure samples of the same chemical compound contain the same elements combined together in the same proportions by mass?


(a) Indivisible

(b) Atoms can neither be created nor destroyed.

(c) Atoms of different elements combine to form a compound. The numbers of various atoms combined bear a simple whole number ratio to each other.

Back

Answer


(a)Atoms were found to be divisible. What names wer given to the particles found inside the atoms?

(b)Give the most important point of the following experiments:

(i) E. Goldstein’s gas discharge tube experiment;

(ii) J. J. Thomson’s cathode ray tube experiment;

(iii) E. Rutherford’s gold foil scattering experiment.

1.2 The Experimental evidence of atomic structure (SB p.4)

(a) Electron, proton and neutron

(b) (i) Discovery of cathode rays

(ii) Discovery of electrons

(iii) Discovery of nucleus in atoms

Back

Answer


The identity of an element is determined by the number of which sub-atomic particle?

Back


The identity of an element is determined by the number of protons in its atomic nucleus.

Answer


(a)Which part of the atom accounts for almost all the mass of that atom?

(b) The mass of which sub-atomic particle is often assumed to be zero?

1.3 Sub-atomic Particles (SB p.7)

(a) Nucleus

(b) Electron

Back

Answer


Are there any sub-atomic particles other than protons, neutrons and electrons?

Back


Other than the three common types of sub-atomic particles (proton, neutron and electron), there are also some sub-atomic particles called positron (anti-electron) and quark.

Answer


If bromine has two isotopes, 79Br and 81Br, how many physically distinguishable combinations of Br

atoms are there in Br2?

Back


There are three physically distinguishable combinations of Br atoms (79Br—79Br, 79Br—81Br and 81Br—81Br) in Br2.

Answer


Write the symbol for the atom that has an atomic number of 11 and a mass number of 23. How many protons, neutrons and electrons does this atom have?


Back

, 11 protons, 12 neutrons, 11 electrons.Na23

11

Answer


Label the different parts of the mass spectrometer.


Back

A – Vaporization chamber

B – Ionization chamber

C – Accelerating electric field

D – Deflecting magnetic field

E – Ion detector

Answer


The mass spectrum of neon is given below. Determine the relative atomic mass of neon.


Back

Relative atomic mass of neon

=

= 20.18

)2.112.0114()2.1122()2.021()11420(

Answer


(a) The mass spectrum of lead is given below. Given that the relative atomic mass of lead is 207.242, calculate the relative abundance of the peak at m/e of 208.


Let x be the relative abundance of the peak at m/e of 208.

(204 1.5 + 206 23.6 + 207 22.6 + 208x) (1.5 + 23.6 + 22.6 + x) = 207.242

x = 52.3

The relative abundance of the peak at m/e of 208 is 52.3.

Answer


(b) The mass spectrum of dichloromethane is given below. Calculate the relative molecular mass of dichloromethane.

Back


The relative molecular mass of dichloromethane

= (84 94 + 85 3.0 + 86 59 + 87 2.2 + 88 13 + 89 2.5 + 90 0.8) (94 + 3.0 + 59 + 2.2 + 13 + 2.5 + 0.8)

= 85.128

The relative molecular mass of dichloromethane is 85.128.

Answer

new way chemistry for hong kong a-level book 11 atomic structure and relative masses 1.1the atomic...

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