1. Objectives

• Define atomicandionic radii, ionization energy, electron affinity,andelectronegativity.

Comparethe periodic trends of atomic radii, ionization energy, and electronegativity, and state the reasons for these variations.

Define valence electrons,and state how many are present in atoms of each main-group element.

Section 2Periodic Trends 2. Atomic Radii

The boundaries of an atom are fuzzy, and an atoms radius can vary under different conditions.

To compare different atomic radii, they must be measured under specified conditions.

Atomic radius - one-half the distance between the nuclei of identical atoms that are bonded together.

Section 2Periodic Trends 3. Atomic Radii Section 2Periodic Trends 4. Atomic Radii

Atoms tend to be smaller as you go from left to right on the periodic table.

This is due to increasing positive charge in the nucleus, pulling the electrons closer to the center.

Atoms tend to be larger down a group.

This trend is due to the increasing size of the electron cloud as electrons fill up larger energy levels.

Section 2Periodic Trends 5. Atomic Radii Section 2Periodic Trends 6. Ion definition Section 2Periodic Trends

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7. Ionic Radii trends Section 2Periodic Trends 8. Ionic Radii trends Section 2Periodic Trends

Positive ions tend to be smaller than neutral atoms.

The larger the positive charge, the smaller the ion.

Again, this is due to increasing positive charge in the nucleus, pulling the electrons closer to the center.

9. Ionic Radii trends Section 2Periodic Trends

Negative ions tend to be larger than neutral atoms.

The more negative the charge, the larger the ion.

This is due to the repelling forces between electrons, causing them to occupy a larger space around the atom

10. Ionization Energy Section 2Periodic Trends

The process to form an ion is called ionization.

The energy required to remove one electron from a neutral atom is calledionization energy .

Sometimes refered to asIE 1 orfirst ionization energy .

11. Ionization Energy Section 2Periodic Trends

Ionization energies increase across a period.

Caused by increasing effect nuclear charge

Higher positive charge more strongly attracts electrons in the same energy level

12. Ionization Energy Section 2Periodic Trends

Ionization energies decrease down a group.

Electrons removed from larger atoms are at higher energy levels, and are farther away from the nucleus.

Electrons are removed more easily due to their distance from the nucleus.

13. Ionization Energy Section 2Periodic Trends 14. Ionization Energy Section 2Periodic Trends

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15. Electron affinity Section 2Periodic Trends

The energy change that occurs when an electron is acquired by a neutral atom is calledelectron affinity.

Electron affinity generally increases across periods.

Electron affinity generally decreases down groups.

All these can be explained by effective nuclear charge and by the distance of an electron from the nucleus.

16. Electron Affinity Section 2Periodic Trends

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17. Valence electrons Section 2Periodic Trends

Compounds form because electrons are lost, gained, or shared between atoms.

Electrons involved in this behavior are calledvalence electrons.

Valence electrons are the outermost energy level electrons in an atom.

Atoms tend to want to have a full set of 8 valence electrons to be stable.

18. Valence electrons Section 2Periodic Trends

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19. Electronegativity Section 2Periodic Trends

Valence electrons hold atoms together in compounds.

In many compounds, the negative charge of the electrons is concentrated closer to one atom than another.

20. Electronegativity Section 2Periodic Trends

Electronegativity is the ability of an atom in a compound to attract electrons from another atom in the compound.

Electronegativity generallyincreases across rows,anddecreases down a group

21. Electronegativity Section 2Periodic Trends

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22. Summary of periodic trends Section 2Periodic Trends