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Periodic Properties of the Elements
Chapter 7 AP Chemistry
I History and Development
Elements in pure form like Gold and Silver were known thousands of years ago
31 elements were known in 1800 by 1865 the number had more than doubled to 63.
The increase lead to the grouping and classification of the elements
First Periodic Law
Properties of elements are a periodic function of atomic weight
Although Meyer also grouped elements like Mendeleev
Mendeleev was given more credit because he left blanks for un-discovered elements
Mendeleev
Modern periodic law In 1913, by using x-ray
spectra obtained by diffraction in crystals, he found a systematic relation between wavelength and atomic number,
Using Atomic number Mosley rearranged the elements noting that the elements were a periodic function of atomic number
Henry Mosley
Design of the Table
Rows and Columns
Horizontal rows – series or periods – numbered 1-7 Notes the shell or principle QN
Vertical columns – group or a family – numbered 1-18 or 1A-8A, 1B-8B
Review electron configuration notation
Periodic Trends
Size of Atoms Within each group the atomic radius tends to
increase as you go down the group – the principle QN increases – size of the cloud gets larger
Within a period the atomic radius decreases as you go from left to right – the effective nuclear charge increases – the number of protons increases while the number of core electrons stays the same – the outer electrons don’t shied each other well
Ionization Energy (I)
I – the energy required to remove the outermost electron from a gaseous atom or ion
I1 – the energy to remove one electron – I2 – the second electron
Metals tend to give up e- to obtain a Nobel gas configuration
Ionization Energy Trends
Ist Ionization energy generally follows effective nuclear charge – increases from left to right in periods and from bottom to top in groups
Except from group 2A to 3A there is a slight increase – the second e- in the S sub-shell is harder to remove that the 1st P e-
GR 5A to 6A there is a slight increase due to repulsion of paired e-s in the P4 configuration
Every element shows large increase in IE when e’s are removed from a Nobel gas core
Electron Affinities
Is the energy change of the reaction of adding an electron to a gaseous atom or ion.
Tends to be an exothermic processes (Delta H is neg) although in some cases it is positive or endothermic
In general electron affinity tends to decrease ( become more negative) from right to left in periods. There is very little change going down a group in the value.
Properties of Metal, Non-Metals & Metalloids Metals – conduct heat
and electricity are lustrous, malleable, and ductile
Tend to lose e’s to become cations
Form basic oxides – metal oxides react with water to produce basic or alkaline solutions
Ex 7.7,7.8 in text
Metal Properties Cont.
Metal oxides + an acid yield a salt and water
Ex 7.9,7.10 in the text
Non-Metal Properties
Poor conductors of heat and electricity are often dull in color and shatter if forged
Nonmetals tend to gain electrons form other sub and become anions
Non-metals from acidic oxides – non-metal oxide react with water to form acidic solutions
Ex 7-12, 7-13 in text Non-metal oxides + a base yield a salt plus
water ex 7.14, 715 in text.
Mettaloids
Boundary between metals and non-metals Mettaloids can either gain or lose electrons Al and Po are metals not mettaloids Properties between metals and non-metals Several are semiconductors and re important
because of their use in circuits and computer chips
Metallic character – increases from left to right and from top to bottom in a group
Group Trends
Alkali Metals Soft, gray metals Low Ionization energies
– lose e’s easily – form +1 cations – very reactive
Electrolysis is a technique to force an electron back on a cation to produce a neutral metal – the metals can be obtained
Alkali Metals
by passing an electrical current through a molten salt. The metals combine with hydrogen to from
hydrides ex. 7.19, or with Sulfur to form Sulfides ex. 7.20 or with chlorine to form chlorides. ex 7.21
The alkali metals react with water to produce hydrogen gas and hydroxides ex 7.22.
See examples of reactions with oxygen ex 7.23-7.25
Alkaline Earth Metals
Slightly harder and more dense than Alkali metals
1st ionization energies are low but not a s low as alkali metals form 2+ cations
Reactivity tends to increase as you progress down a group.
See examples of reactions 7.26 – 7-29
Got Milk?
Trends in Selected Non-metals
Hydrogen Usually placed in grp 1A because of its 1s
electron config. Although a non-metal It reacts with other non-metals to form
molecular cmps ex 7.30-32 Reacts with metals to form hydrides 7.31-32
Oxygen Family
Non-metallic – top of family – metallic at bottom
O, S, Se are typical non-metals – O and S are allotropes – molecules of elements with different structures ( O2, O3, S2, S4, S6, S8)
Polonium is a rare and radioactive element See examples of reactions 7.33-36
The Halogens
All non-metals (astatine is radioactive – seldom discussed)
All are diatomic in gas phase
Bromine normally a liquid – iodine is normally a solid
See reactions 7.37-42
Nobel Gases
Mostly non-reactive Some compounds of
Xenon and Krypton are known
All monatomic gases Highest ionization
energies of any family
xenon tetrafluoride