The Periodic Table
Group
1
2
7
8
Name
Properties
Soft, silver-coloured, solids at
room temp, react strongly with
H2O, stored in mineral oil (to
prevent reacting with O2)
Light, metallic properties, react
Alkaline
with O2 to form oxides, solids at
metals
room temp
S/L/G at room temp, nonHalogens
metallic, v. reactive (esp. with
hydrogen)
G at room temp, low MP/BP, v.
Noble
unreactive
gases
Alkali
metals
• The atomic number (Z) is also the # of
protons for an atom of that element
• The mass number (A) is the sum of the
sub-particles in an atom (protons +
neutrons). Note – electrons weigh virtually nothing,
so they are not included. The # of electrons is the same
as the # of protons!
• You can calculate the # of neutrons by:
# neutrons = A – Z
Mass Number
(bigger)
Atomic Number
(smaller)
A
Z
X
symbol
Element
Ca
Sn
Atomic Atomic # Protons
#
Number Mass
Electrons
20
50
40
119
20
50
20
50
#
Neutrons
20
69
Isotopes
• The same atom with a different atomic
mass. The atomic number, and therefore
the number of protons and electrons in the
atom, does not change
• Eg. Carbon can be carbon-12 and carbon13.
• Some isotopes are more abundant
(common) than others.
Calculating Average Atomic Mass
• Average Atomic Mass =
(Atomic mass x % Abundance)Isotope 1
+
(Atomic mass x % Abundance)Isotope 2
Note: Convert % abundance into decimal value
(eg. 75% = 0.75)
Example 1
Carbon-12 has atomic mass of 12.000000
and % abundance of 98.90
Carbon-13 has atomic mass of 13.003355
and % abundance of 1.10
Av. AM = (12.000000)(0.9810) +
(13.003355)(0.0110)
= 12.011 u
Example 2
Natural neon consists of three stable
isotopes: neon-20 (90.48%), neon-21
(0.27%), neon-22 (9.25%). Calculate the
average atomic mass of neon.
Av. AM = (20)(0.9048) +(21)(0.0027) +
(22)(0.0925)
= 20.1877 u
Trends in the Periodic Table
1. Atomic Radius
•
Distance from center of atom to edge
2. Ionization Energy
•
The energy required to remove one electron
from that atom
Increasing Ionization Energy
Trends in the Periodic Table
3. Electron Affinity
•
Energy change that accompanies the
addition of an electron
4. Electronegativity
•
A number; the tendency of an atom to
attract an electron
Increasing EN and EA