Name: Periods in the Modern Periodic Table
Uploaded: 2019-07-19
Duration: 5 min 31 s
Description: The general characteristics of periods are identified by its total number of shells in an atom or period number. The electronic configuration of an element d...

Question

Give the trends shown by the following properties when we go down a group or from left to right in a period in the modem periodic table &mdash; valency, atomic size, ionisation potential, electronegativity

Accepted Answer

Valency: Valency is defined as the number of electrons needed to complete the octet. While moving across a period from left to right, the valency first increases and then it decreases to zero. And while moving down the group, the valency remains the same as the valence electrons remain the same on moving down the group.

Atomic size: While moving across a period, the atomic size decreases. This is because, while moving across a period, the effective nuclear charge increases. As a result, the outermost shell electrons are pulled towards the nucleus and hence, the atomic size decreases. And while moving down the group, new shells are getting added, therefore, the atomic size increases.

Ionisation energy: Ionisation energy is the energy required to remove the most loosely held electron from an isolated gaseous atom. While moving across a period, due to high effective nuclear charge, more energy is needed to remove the electrons in the outermost shell. Therefore, it increases while moving across a period. While moving down the group, it decreases as the effective nuclear charge decreases.

Electronegativity: Electronegativity is the tendency of an atom to attract the shared pair of electrons towards itself. It decreases while moving down the group and it increases while moving across a period.

$Li$	$Be$	$B$	$C$	$N$	$O$	$F$
$Na$	$Mg$	$Al$	$Si$	$P$	$S$	$Cl$

Give the trends shown by the following properties when we go down a group or from left to right in a period in the modem periodic table — valency, atomic size, ionisation potential, electronegativity

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