Week 2.pdf - Week 2 Lecture 3- Periodic Table • The atom is...

Week 2 Lecture 3- Periodic Table
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The atom is divisible
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Protons, neutrons, electrons, and other subatomic particles
Dimitri Mendeleev
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Russian chemist, uni of St. Petersburg
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1871, Published the periodic table and predicted the properties of 3 new elements
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Gallium, scandium, germanium (1875, 1879, 1886)
Periodic Table of the Elements
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Each row is called a period
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Each row is called a group
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Called periodic table because of Mendeleev's Periodic Law
Mendeleev's Periodic Law
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Properties of elements are periodic functions of their atomic weight
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Trends in the properties of the elements; these are related to their atomic weight and
associated electron structure
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Electron clouds (shells) for each element have a different radius (volume)
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Only a certain number of electrons can reside in any one shell
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Atomic radius goes up and down periodically as you go across the periodic table
3 important factors responsible for these trends:
1. From left to right across a period
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electrons are added to same energy level until filled
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Protons are added to nucleus in order to balance negative and positive particles
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Electrons are attracted more strongly and are pulled closer to the nucleus
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Results in the atomic size (radius) decreasing
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In between groups 2 and 3, there are 10 transition columns
2. Moving down in a group, start to fill more energy levels
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The outermost electrons become less tightly bound to the nucleus
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Results in the atomic size increasing
3. Elements tend to gain or lose outermost (valence) electrons
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To achieve stabled and filled octet (8) formation
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Makes those with 8 valence electrons very stable (inert, noble gases of group VII)
Don’t react with other elements
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These trends explain the periodicity observed in the elemental properties of atomic radius,
ionization energy, electron affinity, and electronegativity

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The periodicity led Mendeleev to organize the elements into the periodic table
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Atomic Radius of an element if half the distance between the centers of two atoms of that
element that are just touching each other
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Ionization Energy: amount of energy required to completely remove an electron from a
gaseous atom
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The closer and more tightly bound an electron is to the nucleus, the more
difficult it is to remove (higher ionization energy)
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Electron Affinity: amount of energy released when an electron is added to a neutral atom or
molecule to form a negative ion
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Electronegativity: describes the tendency of an atom to attract electrons
Summary of Periodic Table Trends:
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Moving left to right
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Atomic radius decreases
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Ionization energy increases
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Moving top to bottom
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Atomic radius increases
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Ionization energy decreases
Molecules
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Two or more atoms joined together by chemical bonds
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Example: H2O, two hydrogen atoms bonded to one oxygen atom
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Molecular weight is the sum of the atomic weights of both atoms
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One mole of water weighs 2 x (1.01g/mol H) + 16.00g/m O = 18.0g/mol H2O
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Example: CaCO3 (calcite) - limestone "rock" made up of mainly calcite
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One mole of calcite weighs 40.078g/mol Ca + 12.01g/mol C + 3 x (16.00g/mol O) =
100.1g/mol
Measurements:
Units and Prefixes
Prefix Symbol Factor Numerically Name
giga G 10
9
1 000 000 000 billion
mega M 10
8
1 000 000 million
kilo k 10
3
1 000 thousand
centi c 10
-2
0.01 hundredth
milli m 10
-3
0.001 thousandth
micro μ 10
-6
0.000 001 millionth
nano n 10
-9
0.000 000 001 billionth
Distance, Mass, Volume
Quantity measured Unit Symbol Conversion
Length.