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MODULE • Chemistry Form 4

3 Changes in physical properties going down the group / Perubahan sifat fizik menuruni kumpulan:
(a) The melting and boiling points are low because the molecules are attracted by weak Van der Waals forces, and small
amount of energy is required to overcome these forces. However the melting and boiling points increase going down
the group.
Takat didih dan takat lebur adalah rendah kerana molekul ditarik oleh tarikan Van der Waals yang lemah, sedikit tenaga diperlukan
untuk mengatasi daya itu. Walau bagaimanapun, takat lebur dan takat didih meningkat menuruni kumpulan.
Explanation / Penerangan:
– The atomic size increases going down the Group 17 because of increasing in number of shell , the size
molecules get larger.
Saiz atom bertambah menuruni kumpulan kerana dengan pertambahan bilangan petala , saiz molekul semakin besar.
– The inter molecular forces of attraction (Van der Waals forces) between molecules become stronger.
Daya tarikan antara molekul (daya Van der Waals) antara molekul semakin kuat.
– More heat is needed to overcome the stronger forces between molecules during melting or boiling.
Lebih banyak tenaga diperlukan untuk mengatasi daya antara molekul yang lebih kuat semasa peleburan atau pendidihan.
(b) Physical properties change from gas (fluorine and chlorine) to liquid (bromine) and to solid (iodine) at room
temperature due to increase in the strength of inter molecular forces from fluorine to iodine.
Keadaan fizik berubah dari gas (flourin dan klorin) kepada cecair (bromin) dan kepada pepejal (iodin) pada suhu bilik kerana
pertambahan kekuatan tarikan antara molekul dari flourin kepada iodin.
(c) The density is low and increases going down the group.
Ketumpatan adalah rendah dan semakin meningkat apabila menuruni kumpulan.
(d) The colour of the elements becomes darker going down the group: fluorine (light yellow), chlorine (greenish
yellow), bromine (brown) and iodine (purplish black).
Warna unsur semakin gelap menuruni kumpulan iaitu flourin (kuning muda), klorin (kuning kehijauan), bromin (perang) dan
iodin (ungu kehitaman).
4 Chemical properties of Group 17 elements / Sifat kimia unsur Kumpulan 17:
(a) All atoms of elements in Group 17 have seven valence electrons and achieve a stable octet electron
arrangement by accepting one electron to form negatively charged ions.
Semua atom unsur Kumpulan 17 mempunyai tujuh elektron valens, mencapai susunan elektron oktet yang stabil dengan
menerima satu elektron membentuk ion bercas negatif .
Example / Contoh:
(i) Fluorine atom receives one electron to achieve stable duplet electron arrangement:
Atom flourin menerima satu elektron untuk mencapai susunan elektron oktet yang stabil:
F + e F –

Electron arrangement / Susunan elektron : 2.7 Electron arrangement / Susunan elektron : 2.8
Number of protons = 9, total charge: +9 Number of protons = 9, total charge: +9
Bilangan proton = 9, jumlah cas: +9 Bilangan proton = 9, jumlah cas: +9
Number of electrons = 9, total charge: –9 Number of electrons = 10, total charge: –10
Bilangan elektron = 9, jumlah cas: –9 Bilangan elektron = 10, jumlah cas: –10
Fluorine atom is neutral . Negatively charged fluoride ion, F is formed.
–
neutral negatif
Atom flourin adalah . Ion flourida, F bercas terbentuk.
–
(ii) Chlorine atom receives one electron to achieve stable octet electron arrangement:
Atom klorin menerima satu elektron untuk mencapai susunan elektron oktet yang stabil:
Cl + e Cl –
Electron arrangement / Susunan elektron : 2.8.7 Electron arrangement / Susunan elektron : 2.8.8
Number of protons = 17, total charge: +17 Number of protons = 17, total charge: +17
Bilangan proton = 17, jumlah cas: +17 Bilangan proton = 17, jumlah cas: +17
Number of electrons = 17, total charge: –17 Number of electrons = 18, total charge: –18
Bilangan elektron = 17, jumlah cas: –17 Bilangan elektron = 18, jumlah cas: –18
–
Chlorine atom is neutral . Negatively charged chloride ion, Cl is formed.
Atom klorin adalah neutral . Ion klorida, Cl bercas negatif terbentuk.
–
(b) All elements in Group 17 have similar chemical properties because atoms in Group 17 have seven valence
electron and achieve the stable octet electron arrangement by receiving one electron to form a negatively
charged ion.

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