• Skip to main content
  • Skip to secondary menu
  • Skip to primary sidebar
  • Skip to footer

CBSE Tuts

CBSE Maths notes, CBSE physics notes, CBSE chemistry notes

  • NCERT Solutions
    • NCERT Solutions for Class 12 English Flamingo and Vistas
    • NCERT Solutions for Class 11 English
    • NCERT Solutions for Class 11 Hindi
    • NCERT Solutions for Class 12 Hindi
    • NCERT Books Free Download
  • TS Grewal
    • TS Grewal Class 12 Accountancy Solutions
    • TS Grewal Class 11 Accountancy Solutions
  • CBSE Sample Papers
  • NCERT Exemplar Problems
  • English Grammar
    • Wordfeud Cheat
  • MCQ Questions

Why does atomic radii decrease going from the bottom left to the upper right of the periodic table?

Why does atomic radii decrease going from the bottom left to the upper right of the periodic table?

Answer:
Two separate trends are occurring.

EFFECTIVE NUCLEAR CHARGE (LEFT/RIGHT)

Across a period, the number of protons and electrons both increase by 1 for each element as we move from left to right. It appears as if no net attractive force is attained.

However, the added electron presents a bit of shielding; each electron can effectively block the others from the positive nucleus. That means an effectively-less negative charge interacts with the positively-charged nucleus, i.e. the net electron charge increases slower than the net nuclear charge does.

So, the nuclear attraction becomes larger from left to right, and the electrons get pulled in more easily.

We say that the effective nuclear charge increases from left to right on the periodic table for the same row.
Why does atomic radii decrease going from the bottom left to the upper right of the periodic table Img 1
We calculate effective nuclear charge as follows:
\(\mathbf{Z}_{\mathrm{eff}}=\mathbf{Z}-\mathbf{S}\)

where \(Z_{\text {eff }}\) is the effective nuclear charge, \(Z\) is the atomic number, and \(S\) is the shielding constant.
Why does atomic radii decrease going from the bottom left to the upper right of the periodic table Img 2
By definition:
\(Z_{e f f}\) is the average attraction of the electron(s) to the proton(s) after accounting for the rapid motion of electrons and the wall of core electrons in between the nucleus and the valence electron in question.

Z corresponds to the number of protons.

S is a value based on degree of “shielding” of the valence electrons from the positively-charged nucleus. For general chemistry, we approximate S as the number of core electrons.

For example, comparing \(Mg\) and \(F\).
Why does atomic radii decrease going from the bottom left to the upper right of the periodic table Img 3
and we have that \(Z_{e f f, F}>Z_{e f f, M g}\), so the atomic radius of \(\text { F (42 pm) }\) is smaller than that of \(Mg(145pm)\). The large difference is also due to having one more quantum level.

As a general rule then (besides for the transition metals), as \(Z_{e f f}\) increases, atomic radii decrease. Thus, since \(Z_{e f f}\) increases from left to right, atomic radii decrease from left to right.

QUANTUM LEVELS (UP/DOWN)

This is a simpler explanation. Each row of the periodic table corresponds to a new quantum level, denoted by the principal quantum number n.
Why does atomic radii decrease going from the bottom left to the upper right of the periodic table Img 4
Each quantum level is farther away from the nucleus than the previous, and is higher in energy. For instance, that’s why the \(3s\) orbital is larger than the \(2 s\) orbital—because \(n=3\) is higher in energy and farther away from the nucleus than \(n=2\).

Therefore, an element on the same column but a new row is automatically larger, because it has another quantum level.

Primary Sidebar

NCERT Exemplar problems With Solutions CBSE Previous Year Questions with Solutoins CBSE Sample Papers
  • The Summer Of The Beautiful White Horse Answers
  • Job Application Letter class 12 Samples
  • Science Lab Manual Class 9
  • Letter to The Editor Class 12 Samples
  • Unseen Passage For Class 6 Answers
  • NCERT Solutions for Class 12 Hindi Core
  • Invitation and Replies Class 12 Examples
  • Advertisement Writing Class 11 Examples
  • Lab Manual Class 10 Science

Recent Posts

  • Understanding Diversity Question Answer Class 6 Social Science Civics Chapter 1 NCERT Solutions
  • Our Changing Earth Question Answer Class 7 Social Science Geography Chapter 3 NCERT Solutions
  • Inside Our Earth Question Answer Class 7 Social Science Geography Chapter 2 NCERT Solutions
  • Rulers and Buildings Question Answer Class 7 Social Science History Chapter 5 NCERT Solutions
  • On Equality Question Answer Class 7 Social Science Civics Chapter 1 NCERT Solutions
  • Role of the Government in Health Question Answer Class 7 Social Science Civics Chapter 2 NCERT Solutions
  • Vital Villages, Thriving Towns Question Answer Class 6 Social Science History Chapter 9 NCERT Solutions
  • New Empires and Kingdoms Question Answer Class 6 Social Science History Chapter 11 NCERT Solutions
  • The Delhi Sultans Question Answer Class 7 Social Science History Chapter 3 NCERT Solutions
  • The Mughal Empire Question Answer Class 7 Social Science History Chapter 4 NCERT Solutions
  • India: Climate Vegetation and Wildlife Question Answer Class 6 Social Science Geography Chapter 8 NCERT Solutions
  • Traders, Kings and Pilgrims Question Answer Class 6 Social Science History Chapter 10 NCERT Solutions
  • Environment Question Answer Class 7 Social Science Geography Chapter 1 NCERT Solutions
  • Understanding Advertising Question Answer Class 7 Social Science Civics Chapter 7 NCERT Solutions
  • The Making of Regional Cultures Question Answer Class 7 Social Science History Chapter 9 NCERT Solutions

Footer

Maths NCERT Solutions

NCERT Solutions for Class 12 Maths
NCERT Solutions for Class 11 Maths
NCERT Solutions for Class 10 Maths
NCERT Solutions for Class 9 Maths
NCERT Solutions for Class 8 Maths
NCERT Solutions for Class 7 Maths
NCERT Solutions for Class 6 Maths

SCIENCE NCERT SOLUTIONS

NCERT Solutions for Class 12 Physics
NCERT Solutions for Class 12 Chemistry
NCERT Solutions for Class 11 Physics
NCERT Solutions for Class 11 Chemistry
NCERT Solutions for Class 10 Science
NCERT Solutions for Class 9 Science
NCERT Solutions for Class 7 Science
MCQ Questions NCERT Solutions
CBSE Sample Papers
NCERT Exemplar Solutions LCM and GCF Calculator
TS Grewal Accountancy Class 12 Solutions
TS Grewal Accountancy Class 11 Solutions