Atomic radius

1. Atomic radius Concepts – electron-shell shielding, electron-electron repulsion, effective nuclear charge

2. This is defined as the half the distance between the nuclei of two atoms that are not bound to the same molecule Why not measure the radius of a single atom? Because an atom is so small, it is really hard to measure a single atom. Nucleus Nucleus What is Atomic radius? Atomic radius Edge of electron cloud Edge of electron cloud

3. Factors affecting atomic radius

4. Explaining increasing atomic radius

5. explaining decreasing atomic radius

6. Atomic radius increases down a group. For every consecutive period, there is an increase in the number of electron shells and inner electrons. This means that there is increased shielding of valence electrons from nucleus by inner electrons. There is also increased electron-electron repulsion among inner electrons. This reduces the effective nuclear charge (that is the attraction between the positive nucleus and the valence electrons) Therefore , the atomic radius increases. Increasing atomic radius Increasing number of shells and inner electrons Atomic radii in periodic table Source: www.camsoft.co.kr/.../VFI_Atomic_Radii_sm.jpg

7. Atomic radius decreases across a period For every consecutive element within a given period, there is an increase in the number of protons and inner electrons. Although the number of electrons is equivalent tl the number of proton, the distance between the electron shell and the nucleus remains the same. This means that there is decreased shielding of valence electrons from nucleus by inner electrons. This results in a contracting of the electron cloud,, resulting in decreasing atomic radius Decreasing atomic radius Atomic radii in periodic table Increasing number of protons with same number of shells Source: www.camsoft.co.kr/.../VFI_Atomic_Radii_sm.jpg

8. electronegativity How atomic radius affects electronegativity

9. The more protons in the nucleus Defining electronegativity • Electronegativity is the ability of an atom to attract electrons to itself. • Dependent on atomic radius and effective nuclear charge • Developed by Linus Pauling (Nobel Prize winner The smaller the atomic radius And the fewer electron shells between the nucleus and the valence (outermost) electrons The effective nuclear charge is the protons’ ability to attract valence (outermost) electrons) And the greater the nucleus’ ability to attract electrons to itself i.e. The higher the electronegativity

10. Fluorine (F) has the smallest atomic radius and therefore the highest electronegativity Francium (Fr) has the largest atomic radius and therefore the lowest electronegativity Atomic radii and electronegativity Source: www.camsoft.co.kr/.../VFI_Atomic_Radii_sm.jpg

11. The most electronegative element is fluorine (F) The least electronegative is francium (Fr) Increasing electronegativity