1. Elemental Properties and Patterns
Periodic Trends
Elemental Properties and Patterns

2. Periodic Trends
There are several important atomic characteristics that show predictable trends that you should know.
Atomic properties—
Deal with only single atoms

3. Atomic Radii
An atom’s size affects chemical and physical properties of an atom
Enables us to gain information on atom’s size
Outer electrons hard to locate
Atom’s size is related to the radius of the atom
Radius of atom = ½ distance between nuclei of 2 adjacent atoms of the same element
Radius is the distance from the center of the nucleus to the “edge” of the electron cloud.
half the distance between the nuclei of 2 bonded atoms.

4. Atomic Radius Trend
Decreases
Increases

5. 1. Metallic Radius
Half the distance between nuclei of adjacent atoms in a metal
Radius of metallic atoms

6. 2. Covalent Radius
Half the distance between the nuclei of 2 adjacent, bonded atoms in a chemical compound.
Atoms MUST be identical
Radius of nonmetallic atoms (Ex. Cl2. Br2)
Smaller radii than metallic—covalent bonds hold the atoms close
Ex. Br2 Å
1.43 Å

7. 3. Ionic Radii
Ions
Atoms that have gained or lost electrons (anion, cation)
Electrons gained/lost from valence shell (outer electron shell)
Defined by the distance between the nuclei of 2 ions
Studies with crystal structures
Radii related to original atomic radii

8. Ionic Radii (cont.) 1) Anions LARGER size than original neutral atom
Generally nonmetals
Additional electrons cause the atom’s size to increase
Electrons repel as increase in number, causes size to increase

9. Ionic Radii (cont.) 2) Cations SMALLER size than original neutral atom
Generally metals
Removal of electrons causes the atom’s size to decrease
more attractive force from nucleus, nucleus can pull remaining electrons towards it.

10. Atomic Radius
The effect is that the more positive nucleus has a greater pull on the electron cloud.
The nucleus is more positive and the electron cloud is more negative.
The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

11. Identify the atom with the largest radii
1) Ca, F
2) Cl, O
3) N, P

12. Electron Shielding Repulsive forces exist between electrons.
Electrons are found at various distances from the nucleus
Electrons closer to the nucleus (at lower energy levels) can “screen/shield” outer electrons
Outer electrons do not feel the attractive force from the nucleus as a result
Affects periodic trends such as ionization energy
Explains why ionization decreases down a column

13. Ionization Energy
If an electron is given enough energy (in the form of a photon) to overcome the electrical forces holding it, the electron can be removed from the atom completely.
Amount of energy needed to remove ONE electron from a neutral atom
Removal from ground state in neutral atom of gaseous state to form positive ion

14. Ionization Energy (cont.)
The energy required to remove an electron from an atom is ionization energy.
Formation of positive ions (cations)
The larger the atom is, the easier its electrons are to remove.
Ionization energy and atomic radius are inversely proportional.

15. Ionization Energy (cont.)
1st ionization energy
Energy required to remove 1st electron from atom
Taken from highest energy level
Easiest to remove
Energy increases as more electrons are removed

16. Ionization Energy Trend
Increases
Decreases

17. Ionization Energy

18. Identify the highest ionization energy
F, Mg
Na, Rb
P, O

19. Classwork: Ionization Energy
Circle the atom with the highest first ionization energy.
Al, B 5) Fr, Li 9) Se, Cl
Mg, Na 6) Mg, Al 10) Rb, Mg
P, As 7) C, F
I, At 8) K, Sc

20. What does affinity mean?

21. Electron Affinity
energy change that occurs when electrons are added to a neutral atom
Some atoms will release energy, others will absorb energy to “force” electron into atom
Ex. Hot Potato
Greater value with smaller atoms
Energy released when electron added
Exothermic, negative value
An atom’s “desire/affinity” for more electrons, wants to get more electrons ! ! !
Metals—decrease electron affinity.
Nonmetals—increase electron affinity, more reactive
Stable atoms—full octet

22. Electron Affinity Trend
Increases
Decreases

23. Electronegativity increases decreases
trait or characteristic of an atom
Ability of an atom to pull electrons toward it, how tightly an atom wants to hold onto its electrons
Atom’s ability to attract electrons from another atom
Periodic Trend:
increases
decreases

24. Practice: Which atom is more electronegative?
Lithium or fluorine
Chlorine or iodine
Magnesium or oxygen
Calcium or barium
Rubidium or Strontium F Cl O Ca Sr

25. Metallic Character
This is simply a relative measure of how easily atoms lose or give up electrons.
Tendency to LOSE electrons
Related to atomic radius/ionization energy, how easy to remove electrons

26. Metallic Character Atoms with a tendency to LOSE electrons Decreases
Increases

27. Nonmetallic Character
Atoms with a tendency to GAIN electrons
Increases
Decreases