trends in the periodic table dmitri mendeleev in 1869 mendeleev and lothar meyer (germany) published...
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TRENDS IN THE PERIODIC TABLE
Dmitri Mendeleev In 1869 Mendeleev and Lothar Meyer (Germany) In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical classification schemes for published nearly identical classification schemes for elements known to date. The periodic table is base on elements known to date. The periodic table is base on the similarity of properties and reactivities exhibited by the similarity of properties and reactivities exhibited by certain elements. Later, Henri Moseley certain elements. Later, Henri Moseley ( England,1887-1915) established that each elements ( England,1887-1915) established that each elements has a unique atomic number, which is how the current has a unique atomic number, which is how the current periodic table is organized.periodic table is organized.
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The Periodic Law
• When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.
• Horizontal rows = periods– There are 7 periods
• Vertical column = group (or family)– Similar physical & chemical prop.– Identified by number & letter (IA, IIA)
Across the Periodic Table• Periods: Are arranged horizontally across the Periods: Are arranged horizontally across the
periodic table (rows 1-7)periodic table (rows 1-7)• These elements have the same number of valence shells.These elements have the same number of valence shells.
1IA
18VIIIA
12
IIA13
IIIA14
IVA15VA
16VIA
17VIIA
2
33
IIIB4
IVB5
VB6
VIB7
VIIB8 9
VIIIB10 11
IB12IIB
4
5
6
7
2nd Period
6th Period
Down the Periodic Table•Family:Family: Are arranged vertically down the periodic table Are arranged vertically down the periodic table (columns or group, (columns or group, 1- 18 or 1-8 A,B)1- 18 or 1-8 A,B)•These elements have the same number electrons in the outer most shells, the valence shell.These elements have the same number electrons in the outer most shells, the valence shell.
1IA
18VIIIA
12
IIA13
IIIA14
IVA15VA
16VIA
17VIIA
2
33
IIIB4
IVB5
VB6
VIB7
VIIB8 9
VIIIB10 11
IB12IIB
4
5
6
7
Alkali Family: 1 e- in the valence shell
Alkali Family: 1 e- in the valence shell
Halogen Family: 7 e- in the valence shell
Halogen Family: 7 e- in the valence shell
All Periodic Trends
• Influenced by three factors:
1. Energy Level– Higher energy levels are further away from the
nucleus.
2. Charge on nucleus (# protons)– More charge pulls electrons in closer. (+ and –
attract each other)• 3. Shielding effect
Shielding• The electron on the outermost
energy level has to look through all the other energy levels to see the nucleus.
• The inner electrons shield the outer electrons from the pull of the nucleus. This effect is known as electron shielding
• Second electron has same shielding, if it is in the same period
What do they influence?
Energy levels and Shielding have an effect on
the GROUP ( )
Nuclear charge has an effect on a PERIOD
( )
Atomic Radius
• Average distance from the nucleus to the electron cloud.
• The electron cloud doesn’t have a definite edge.
• They get around this by measuring more than 1 atom at a time.
© 1995-2002. Prentice-Hall, Inc.
#1. Atomic Size - Group trends• As we increase the
atomic number (or go down a group). . .
• each atom has another energy level,
• so the atoms get
bigger.
HLi
Na
K
Rb
#1. Atomic Size - Period Trends• Going from left to right across a period, the size
gets smaller.
• Electrons are in the same energy level.
• But, there is more nuclear charge.
• Outermost electrons are pulled closer.
Na Mg Al Si P S Cl Ar
Atomic Radius
Trends in Ionic Size: Cations• Cations form by losing
electrons.• Cations are smaller than
the atom they came from – not only do they lose electrons, they lose an entire energy level.
• The ionic radius decreases as the nuclear charge on the ion increases
Cation Group trends
• Each step down a group is adding an energy level
• Ions therefore get bigger as you go down, because of the additional energy level.
Li1+
Na1+
K1+
Rb1+
Cs1+
Ionic size: Anions
• Anions form by gaining electrons.
• Anions are bigger than the atom they came from – have the same energy level, but a greater area the nuclear charge needs to cover
Ion Period Trends• Across the period from left to right, the nuclear
charge increases - so they get smaller.
• Notice the energy level changes between anions
and cations.
Li1+
Be2+
B3+
C4+
N3-O2- F1-
Ionization Energy • Energy needed to remove an electron from a
neutral atom
• Period - First ionization energy increases as you go from left to right across a period.
• Why?
• Group - ionization energy decreases as you go down a group.
• Why?
ELECTRON AFFINITY• Energy change that occurs when an electron is added to an
atoms outer level to form a negative ion
• Period - electron affinity (EA) increases from left to right across the periodic table
• Why?
• Group - electron affinity decreases down a group• Why?
ELECTRONEGATIVITY
• a quantitative measure of the electron-attracting ability of an atom in a molecule
• Period - electronegativity across a period
• Group - electronegativity down a group
• The most electronegative element is fluorine. What is the least electronegative element?
Trends in the Periodic Table
© 1995-2002. Prentice-Hall, Inc.