The Periodic Table

Atomic Radius (radius of an atom)◦ atomic radius is measured (just like any other radius)◦ the atomic radius of an atom increases each period and decreases from

group to group◦ The shielding effect is how the atomic radius of an atom decreases

from left to right on the periodic table

Ionic Radius (radius of an ion)◦ ions have a different radius than their non-ionic counterparts.

Example: H+ has a different radius than H because it has no electrons◦ protons pull electrons towards the center, preventing them from

escaping orbit◦ electrons pull away from the center because they are in constant motion

cations are smaller than their neutral form because they have more protons than electrons (more protons means more force keeping electrons in)

anions are larger than their neutral form (more electrons means they can orbit further away)

Periodic Trends

Ionic Radius

Ionization Energy and Electronegativity Ionization Energy is the amount of energy required

to lose an electron from a regular atom (how easily it will give up an electron)

Electronegativity/Electron Affinity is an atom’s ability to draw electrons toward it when it has a chemical bond

ionization energy and electronegativity share the same patter on the periodic table◦ They both increase as the group number increases, but

decreases as the period number increases

Periodic Trends

Periodic Trends

Valence electrons are the electrons that occupy the highest energy level (1-7) of the electron cloud.◦ The highest energy level is equal to the period

Example: ◦ Carbon has the electron configuration 1s2 2s2 2p2.◦ Carbon belongs to period 2, so its highest occupied

energy level is 2.◦ Carbon’s 2nd energy level has 2 electrons in

sublevel s and 2 electrons in sublevel p, therefore carbon has 4 valence electrons

Valence Electrons

Group 1 has 1 valence electron Group 2 has 2 valence electrons Groups 3-12 (transition metals) vary Group 13 has 3 valence electrons Group 14 has 4 valence electrons Group 15 has 5 valence electrons Group 16 has 6 valence electrons Group 17 has 7 valence electrons Group 18 has 8 valence electrons

Valence Electrons

Ionization – The formation of an ion

Groups 1-14 elements make cations ◦ These ions ALWAYS have 0 valence electrons

Groups 14-17 elements make anions◦ These ions ALWAYS have 8 valence electrons

Group 18 elements (noble gases) don’t make ions because they already have 8 valence electrons

The charge of an ion can be determined from the number of valence electrons◦ 1 valence e- makes a +1 charge because it had to lose 1 electron to equal

zero◦ 6 valence e- makes a -2 charge because it had to gain 2 electrons to equal 8◦ 4 valence e- makes either a +4 or a -4 charge, depending on the element

Formation of Ions

Formation of Ions

Group 1 Alkali Metals: Most metallic and reactive group◦ form +1 cations

Group 2 Alkaline Earth metals: Very reactive group◦ form +2 cations

Block D Transition Metals: Semi-reactive◦ form cations with different charges

Block F Lanthanides and Actinides: Radioactive and extremely heavy metals

Group 16 Chalcogens: Very reactive and electronegative◦ form -2 anions

Group 17 Halogens: Extremely reactive and electronegative group◦ form -1 anions

Group 18 Noble Gases: Completely unreactive because of complete valence shell

Properties of Groups

There are 3 types of elements: metals, metalloids and nonmetals

◦ 1) S, D and F block Metals: Malleable (can change shape without breaking), shiny, conducts electricity

◦ 2) P Block Metalloids: Show both metallic and non-metallic character. Metalloids touch the staircase of the periodic table

 ◦ 3) P Block Nonmetals: dull, brittle, and poor at conducting

electricity because they hog electrons

Note: metallic character trend follows the same pattern as atomic radius

Types of Elements

Mendeleev was the scientist responsible for seeing the pattern of properties of the elements in the periodic table

◦ he was the first to organize those elements into periods and groups.

◦ Elements within the same group have the same physical and chemical properties.

◦ When he organized his version of the table, there were holes in it because there were only 60 out of 110 known elements at the time. After he died, the holes were later filled by newly discovered elements, verifying what he knew to be correct:

you can predict how an atom will behave by knowing where its atomic number falls on the periodic table.

Periodic law – Both physical and chemical properties of the elements are functions of their atomic numbers.

History