Chapter 5: The Periodic Law

States that the physical and chemical properties of an element are periodic functions of thier atomic numbers

Cannizzaro - found method of standard relative massive
Meendelev - 1st periodic table, no noble gas group
- arranged by mass/properties
- empty spaces = undiscovered elements
Moseley - arranged table by increasing atomic numbers
- current table being used
- periods (horizontal), families (vertical)
- periodic law

Group 1/1A
highly reactive
soft nonmentals
H, Li, Na, K, Rb, Cs, Fr
1 valence electron
oxidation number is always +1
S block, ns¹
not found as free elements in nature
Fr = most metallic

Group 2/2A
less reactive than group 1
2 valence electrons, high ionization energy between 2nd and 3rd levels
S block, ns²
metals; this & group 1 have lower electronegative values
Be, Mg, Ca, Sr, Ba, Ra
harder, more dense, stronger than alkalis

D block, groups 3-12
4s, 3d...
in deviations, sum of outer s+d electrons = group number
metallic, good conductors
platinum, gold, palladium = least reactive
atomic radius decrease across period; less than that of main group b/c d sublevels add more shielding
ionization energy increase for periods & groups (1st IE) because electrons available for ionization in outer s sublevel is less shielded from nucleus charge by electrons in incomplete d sublevels.
have electronegative values between 1.1 and 2.54
get rid of S first, then P
most form 2+ ions

1/2 distance between nuclei of identical atoms that are bonded together.
TRENDS
Period: Decreases bc of increasing positive charges in nucleus. pulls electrons closer.
Family: increases b/c electrons occupy sublevels in higher main energy levels

Measurements = kJ/mol
A + energy --> A⁺ + e^-
endothermic, requires energy
electrons can be removed if sufficient energy
energy required to remove 1 electron from neutral atom of an element = ionization energy
TRENDS
Period: Nonmetals have higher ionization energies than metals;
Increases bc of increasing nuclear charge; attracts electrons in same energy level
Family: decreases because electrons in higher energy level, further from nucleus, more electrons between nucleus and outer as atomic number increases.