General Features of the Periodic Table

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General Features of the Periodic Table

• Periods (Horizontal)
• Groups (Vertical)
• Representative elements
• Transition elements
• Metals
• Alkali metals
• Alkaline earth metals
• Non-metals
• Halogens
• Inert
• Metaloids

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The Atom
Units of mass atomic mass unit (amu) Defined as
1/12 of the mass of a carbon atom
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Structure of the atom
The gold foil experiment Showed that most of the
atom is empty space with a dense nucleus
Ernest Rutherford (1871-1937)
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Q. What distinguishes elements?

• Number of PROTONS in nucleus
• Given by Atomic Number

Carbon has 6 p
Oxygen has 8 p
Because atoms are electrically neutral, number p
number of e-
So, carbon also has 6 e-
and oxygen also has 8 e-
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• Mass number (number p) (number n)

(in amu)

• What is the element with 13 p and 14 n?
• How many e- does this element have?

Al
13
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Isotopes

• Definition Atoms with the SAME number of p but
  DIFFERENT number of n.

Mass number (top) (p n)
Atomic number (bottom) (p)
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Atomic Mass

• Reported (periodic table entries) are weighted
  averages of masses of all known isotopes, based
  on abundance

i.e., if there is more 35Cl than 37Cl on earth,
atomic mass of Cl will be closer to 35 amu than
to 37 amu.
75.8 of Cl is 35 24.2 of Cl is 37
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So where is the electron???
Heisenberg's Uncertainty PrincipleWerner Karl
Heisenberg (1901-1976) stated in 1927 that
certain specific pairs of variables cannot be
measured simultaneously with high accuracy. Most
importantly, he pointed out that within an atom,
it is possible to measure the position, or the
momentum, of a subatomic particle such as an
electron. However, it is not possible to measure
both of them at the same time, because the
measuring process interferes to a substantial
degree with what is being measured.
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Electron Configuration

• Main Energy Levels (Shells)
• n 1, 2, 3, 4(Whole integers)
• Shells contain SUBSHELLS
• These are denoted as s, p, d, f
• Number of subshells in shell shell number (n)
• So.
• there is 1 subshells in Shell n 1 and
• 2 subshells in Shell n 2
• 3 subshells in Shell n 3 etc. Get it?

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Orbitals

• Subshells consist of defined regions of space, in
  which electrons can exist
• Each has a specific shape
• Each can accommodate a finite number of
  electrons
• Maximum number of electrons 2n2

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p subshell 3 orbitals 6 electrons
f subshell 7 orbitals 14 electrons
d subshell 5 orbitals 10 electrons