1972-11-24 — Page 26

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頁二第張七第 日九十月十年子壬麻夏

WAH KIU YAT PO

五期星

日四廿月一十年二七九一腊公年一十六國民華中育教儒割

1973英文中學會考試題預習專欄

化學科

(五)

Chemistry 5

Blectronic arrangement and periodo table

Electronic Energy Levels

The energy levels are number- Jed, starting with the lowest as 1,

the next higher as 2 etc. The number of energy level, is usually designated by h. Each principal energy level shell is again sub- divided into sub-levels. In the n1 shell, there is only one sub-level, (S). In the n = 2 shell, there are two sub-levels, (S,P). in the n = 3 shell, there are three sub-levels (S,P and d) and so on,

Solution for last week

Element by wt.

atomic wt, relative no: of atom

simplest ratio,

of atoms:

Sodium 43.4

Carbon

11.3

Oxygen [45.3

noco

AMAH

Elements in

(2n)

sub-level,

Max.No.of

electrons

in sub-levels.

1

2882

KARZ

Energy

Principal

Letter

Max.No. of

levels

Quantum

Number

n

n = 2

P,d,f}

alomic Volume

12

B. Periodicity of properties a. periodicity of valency of elements:

1) valency towards hydrogen and j

chlorine b

Elements an Group 1 TO LV and VIII, the valency is equal to the number of the Group; in Group V to

(8 it is equal tu

the number of Group). Example: In 2nd period

H 10H

HN HO

Group

II

Il

Element Li

Valency

Be

III

Compound Lil BeCl2 BC13

IV V VI

VII

VIII:

atomic we

11) Other physical properties showing similar characteristics are malleability, ductility and electrical conductivity

Isotopes:

Atoms having the same number of protons but different number of neutrons are called isotopes. For examples: 350 and 370 are the two

istopes of chlorine. Isobars

-- Atoms of the same mass number but different atomic, numbers are

40% balled isobars, e.ɛ• 1847, 195

Exercise

Part I

1. Which of the following has the most dominating influence on the

properties of an atom?

A. the number of neutrons in its

nucleus.

B. the number or protons in its

nucleus.

C. the atomic wo. of the atom, D. the electronic configuration of

the aton.

E. the total number or runc tional

particles composing the atom.

2. In which of the following cases

do both element have similar pro-, perties because of equal numbers of electrons in the outermost? orbit of their atoms?

A. O & N

B. Cr & A2

0. C & B

B

Therefore the simplest Na2CO3

2. Fes + 2HC1FeCl + H2

mol.wt.

55.85+

87.85

2.2

+32 34

34 gm Hydrogen sulphide i produced from 87.85 gm. of ferrous sulphide

The

wt. of Hydrogen sulphide is produced from 3.2 m. ferrous sulphide is:

34 x 2.2.

0.85.

2 The structure of atoms.

of

The structure of atom will be summarized as follow:

Atoms of any element are made up of three kinds of particles called the electrons, protons and neutrons. These particles arrange themselves in a general pattern as:

Nucleus

Protons &

neutrons

are here

/V,L,M,N, O, P, Q, Are orbits in

which electrons are circulating.

The electrons circulate with great velocity in orbits around the nucleus of the atom. orbits are called "energy leal or "shells"

Thege

A proton carries 1 unit of positive change and an election carries 1 unit of negative change; but neutrons have no change. In an atom, the numbe of protons is always equal, to the number of electrons. D. The proton and the neutron have

about the same weight but the electron is only about

1840

the weight of the proven. So the atomic weight equal to the sum of the protons and neutrons, The number of protons in the nucleus is referred to as the "atomic number" of the element. e.g. 7, 16

Electrons distribution of elements in periodic table.

(1) The maximum number of electroar that can be contained in a given shell-

(2) The outermost shell is limited to 8 electrons and the next to the outermost shell is limited to 18 electrons.

A. Electronic Configuration;

Element Atomic No.

principal shell sub-levels

Electronic Arrangement

K.

•1 = 2

12

n = 2

15 25

T

Ř A UZ

457

0

152 252

Is?

1s2 252 2p6

152 282

0.1

Ne

11) Valency towards oxygen

The Maximum valency of an

element is equal to the number of the Group in which it occurs Example: In 3rd period

V VI VII

VIIL

AIIIE

9

Valency

Na

Mg

PARE

Compound Na 0 Ngo Al20 $102 F205 S03 C1207

2

3

D. 5 & 01

B. Na & 01

3. Atomic number can be defined as

1. the other of elements when

arranged according to their mass number.

the unmber of electrons in an unionised at on

3. the number of protons in the

element

the number of neutrons in an atom

5. the number of protons in an

atom

A. 1,2,3

B. 2,3,4

C. 3,4,5

D. 2,5

E.

isotopy

But the elements of the higher, numbered Group may often exercise a lower valency in oxides, as well as the maximum valency. For example: Nitrogen in N, O, NO

and TO2, Sulphur in su etc.

D. Periodicity of physical proper-

ties:

a) atomic volume as the figure.

E. 2,4

4. An element which possesses atoms of similar chemical properties · but different weights is said to: show

A. allotropy. B. periodicity C. isomerism

D. isomorphis

5. The chemical properties of an element depend on the number of

A. protons only B. neutrons only C. protons and neutrons together D. electrons in the innermost shell E, electrons in the outermost shell 5. Which statements are correct concerning these two isotopes?

40

184r and

Ar has i

404 2018

ULURUHN ELIR 4- neutrons per atom in the

isotope

2. Both isotopes have 40 electrons

per atom

3. Both isotopes have mase numbers

Of 40

4. They are isobars

1,2, Q1,3,4

R. 2,3

S. 3.4

T. 1,2,3

7. A certain element has an atomic number of 16 and a mass number of 32. How many neutrons are there in the nucleus of an atom of the element?

P. 0: QU 18.

III

Group

апашата

R 16

S. 32

T

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