Agenda Block 4 Attendance Make Groups for element assignment Get into your groups Preform your trend Powerpoint Homework-Part C and Part D.

Agenda Block 4• Attendance• Make Groups for element assignment• Get into your groups• Preform your trend• Powerpoint • Homework-Part C and Part D

Periodic Table Trends

WooT Get Excited!!!

PERIODIC TRENDS:

Periodic trend - when many properties of the elements change in a predictable way as you move through the periodic table.

Atomic and Ionic Radii:

Atomic size is usually described by the radius of an atom.

Atomic radii - atomic radius usually determined by the distance between the nuclei of metal atoms in a crystal. (X-ray diffraction)Trend-

Ionic radii Def’n- is a measure of the size of the electron probability volume for an ion.

i.e. Charged molecules will vary in size as electrons are received or lost.

Atoms get larger going down a group. Atoms get smaller moving from left to right across each period.

Why does radius get smaller as # of electrons increases as you move across a period?

-higher atomic number - more protons-more protons - more positive charge-increased force of attraction causes negative electrons to move closer to the nucleus

Why does radius get larger as you go down a group?-number of electrons increases-orbitals further and further from the nucleus-repulsive forces from inner electrons shields outer electrons from attractive forces of the nucleus. (Shielding effect)

Shielding Effect

• Decrease in attraction between an electron and the nucleus in any atom with more than one electron shell.

Ionization Energy:Def’n- the minimum amount of energy needed to remove the most loosely bound electron from a gaseous atom to form an ion with a 1+ charge

element(g) + ionization energy --> Ion+(g) + e-

• Ionization energies enable scientists to predict which elements may form the positive ions in ionic substances.

• Lower IE most likely to be positive ion.

• Atoms with high ionization energies hold onto their electrons very tightly.

ex Noble gases - highest IE Alkali metals - lowest IE

** ionization energies decrease as you move down a group. Ionization energies increase as you move from left to right across a period. **

The difference between 1st, 2nd, and 3rd ionization energies is the increase in energy for every electron removed. (1st 2nd and 3rd)

ex Magnesium 3rd IE is considerably higher because the first 2 are valence electrons.

Ionization energies:

-decrease as you move down a group.

-increase as you move from left to right across a period.

Electron Affinity:

Def’n- The amount of energy absorbed when an electron is added to an atom to form an ion with a 1- charge.

Elements with very negative electron affinities gain electrons easily to form negative ions (anions)

• In general, non-metals have more negative electron affinities than the metals do. Non-metals release energy when they gain electrons. Metals have to gain energy before they gain an electron.

• ** electron affininity is more negative as you move up a group. EA is more negative as you move from left to right across a period**

Electronegativity: Def’n- An atom’s ability to attract electrons in a chemical bond.

Fluorine is the most electronegative element (4.0). Cesium and Francium have the least electronegativities (0.7).

• Electronegativity is used to make predictions about bonding.

• Large differences in EN react to form ionic compounds

• Small difference in EN usually form covalent compounds

• ** electronegativities usually increase from left to right across periods and from bottom to top within groups.**

Metallic Properties:

• General properties of metals increase from right to left across periods and from top to bottom within groups.