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