Page 16 - Chemistry ICSE Class X

4 ICSE Chemistry – 10
Periodic Properties and Their Variations in Groups

and Periods
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following periodic properties of elements, and their variations in groups
Gold and platinum are called noble and periods:
metals because of their limited ƒ Atomic size (or atomic radius)
reactivity. ƒ Metallic character
ƒ Nonmetallic character
ƒ Ionisation potential (or ionisation energy)
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ƒ Electronegativity
What are the causes of periodicity
While studying the modern periodic law, we have learnt that the chemical
and physical properties of elements are the periodic functions of their
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elements are written as a function of their atomic numbers, similar outer
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periodicity in the properties of elements (QT GZCORNG CNN CNMCNK OGVCNU
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In this section, we describe the periodic properties of elements and
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Atomic Size

How is the atomic size described
The atomic size of an element can be expressed as the radius of its atom
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“The distance from the centre of the nucleus to the outermost shell
of electrons in an isolated atom is called its atomic radius.”
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“Half the distance between the nuclei of the two similar atoms
covalent bonded to each other by a single bond is called its atomic (or
covalent) radius.”
For example, the H – H covalent bond has a length of 74 pm (pm is
called picometre; 1 pm = 1 × 10 –12 O 5Q
74 pm
Atomic radius of hydrogen atom = = 37 pm
2
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Fig. 1.1 Atomic (or covalent) radius of “Half of the distance between the nuclei of the two adjacent metal
H atom atoms in the metallic crystal is called its atomic radius.”