The Periodic Table

Mendeleev (1869) used valence and atomicweight to organize elements into periods.He did this through recognition that thevalences rose and fell in regular patterns

Meyer (1870) recognized a periodicitybetween atomic volumes and atomicweights

• Rows are periods numbered in relative to the firstquantum number of the orbitals being filled withincreasing atomic number– First period – electrons in 1s orbital– Second period – electrons in 2s, 2p orbitals– Third period – electrons in 3s, 3p orbitals– Fourth period – electrons in 4s, 4p, plus 10 elements filling 3d

orbitals– Fifth and sixth periods – similar to fourth in terms of filling d

orbitals– 6th period also contains 14 extra elements called the rare earths,

containing electrons in the 4f orbital– 7th period has 14 extra elements called the actinides containing

electrons in the 5f orbital

• Elements in s and b blocks form the AGroup

• Elements in d block formed the B Group

• Group IA - +1 valence – Alkali metals,except Hydrogen

• Group IIA - +2 valence – Alkaline metals• Group VIIA - +7 valence: five in p orbital

and 2 in s orbital– In nature these actually pick up one electron

to form a -1 valence• Noble Gases – all orbitals filled – valence

= 0

• Transition metals– Group IB – d10s1 – valence +1

• 1s2,2s2, 2p6,3s2,3p6,3d10,4s1 = Cu– Group IIB +2 ions– Group IIIB – valence +3

• 3d1,4s2 = Sc– Group VIIB – valence +7,+6,+4,+3,+2– Sd5,4s2

• Group VIIIB- Fe, Co, and Ni areanomalous– Should be valence +8 based on 3d6,4s2

However, valence is actually +2 and +3• Remainder of platinum group elements

have valence of +2, +3, +4, +6, +8

Periodic Law

• Chemical and Physical properties ofelements are similar with increasingatomic number

• Elements in Groups have similar valencesbecause they have similar electronicstructures– This leads to similar physical and chemical

properties within groups

Atomic Number and Atomic MassNumber

• Atomic Number = z = number of protons innucleus

• Atomic Mass Number = A = Z+N– 12

6C• Atomic Mass Unit – AMU = 1/12 of the

mass of 126C– The most abundant stable isotope of carbon

Atomic Weight, Gram AtomicWeight, Gram Molecular Weight

• Atomic weight = sum of mass ratio ofnaturally occurring isotopes– Atomic weight is dimensionless because it is

expressed relative to the mass of carbon• Gram atomic weight = atomic weight in

grams• Gram molecular weight and gram formula

weight = molecular weight in grams

• Both Gram Atomic Weight and Gram Molecularweight are referred to as the mole (mol)– Basic unit of mass of elements and compounds

• 1 mol = fixed number of atoms or molecules• NA = 6.022045 x 1023 atoms or molecules/mole –

Avagadro’s Number– 1 mol of a substance contains as many basic units as

there are atoms in 0.012 kg of carbon-12

• The relationship between moles, atomicweight and Avagadro’s Number allows usto represent reactions by equations2H2 + O2 >>>> 2H2O

2 mol = 1 mol >>>>>>>>> 2 mol

2 g + 1g does not yield 2 gram water

Molecular Weight of Compounds

• BaSO4 (barite)• Ba – 137.3400 g/mol• S – 37.064 g/mol• O – 15.9994 g/mol• Barite – 233.4016 g/mol• Solubility in cold water for barite = 2.22x

10-4 g/100 mL

Molecular Weight of Compounds

• BaSO4 >>>>>>>>>> Ba2+ + SO42-

1mol 1 mol + 1 mol

2.22 g/L divided by 233.4016 g/mol = 9.512 x 10-6

mol/L

9.512 x 10-6 mol/L x 137.34 g/mol = 1.3064 g Ba2+

Number of ions in solution = 9.512 x 10-6 x6.022045 x 1023 = 5.778 x 1018 ions/L

Gram Equivalent Weight

• Gram equivalent weight = gram atomicweight or gram molecular weight dividedby valence

• For acids and bases:• Gram equivalent weight = gram molecular

weight divided by the number of hydrogenion or hydroxyl ion groups when the acidor base is dissociated in fluid

Gram Equivalent Weight for Ca2+

• Atomic weight calcium = 40.08 g/mol• Valence = +2

• Gram equivalent weight = 40.08 (g/mol)/2= 20.04 equivalents (eq)

For Acids

• H2SO4 it is ½ the molecular weightbecause 2 H will dissociate in fluid–½ molecular weight = 49.04 eq

• H3PO4 it is 1/3 the molecular weightbecause 3 H will dissociate in fluid– 1/3 molecular weight = 32.67 eq