Transcript Periodicity Glencoe Chapter 6

Periodicity
Glencoe
Chapter 6
Development
of the
Modern Periodic Table
1790s – 23 known elements
By 1870s – 70 known elements
1864 - John Newlands proposed arrangements by mass
and properties by octaves
1864 – Lothar Meyer proposes arrangements by mass
and columns of properties—but doesn’t publish!
1869 – Dmitri Mendeleev also proposed arrangements
by mass and columns of properties—and announces!
1913 – Henry Moseley proposed arrangements by
atomic number. (periodic law)
Newlands’ “octaves”
H1
F8
Cl 15
Co/Ni 22
Br 29
Pd 36
I 42
Pt/Ir 50
Li 2
Na 9
K 16
Cu 23
Rb 30
Ag 37
Cs 44
Tl 53
Gl 3
Mg 10
Ca 17
Zn 25
Sr 31
Cd 34
Ba/V 45
Pb 54
Bo 4
Al 11
Cr 18
Y 24
Ce/La 33
U 40
Ta 46
Th 56
C5
Si 12
Ti 19
In 26
Zr 32
Sn 39
W 47
Hg 52
N6
P 13
Mn 20
As 27
Di/Mo 34
Sb 41
Nb 48
Bi 55
O7
S 14
Fe 21
Se 28
Ro/Ru 35
Te 43
Au 49
Os 51
Shortly after, his ideas were presented to the Russian Physico-chemical Society. They were read by Professor Menschutkin because
Mendeleev was ill. His ideas were then published in the main German chemistry periodical of the time, Zeitschrift fϋr Chemie.
The world’s first view of Mendeleev’s Periodic Table – an extract from Zeitschrift fϋr Chemie, 1869. Click here for a translation
Key “landmarks”
of the
modern periodic table
Periods (horizontal)
Groups/families (vertical)
Representative elements

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s & p block
Groups 1A – 8A
Groups 1,2,13,14,15,16,17,18
Transition elements

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
d block (f block = “inner transition elements”)
Groups 1B – 8B
Groups 3 - 12
Other notable classifications:
Metals


Alkali (group 1)
Alkaline (group 2)
Metalloids
Nonmetals

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Halogens (group 17)
Noble gases (group 18)
Organizing Elements by Electron
Configuration
Valence Electrons

Atoms in the same group have similar
chemical properties b/c they have the same #
if valence electrons
Valence Electrons and Periods

Energy level of valence electrons indicates
the period on the PT
Valence Electrons and Group Number

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Group # = # valence electrons
Exception: Helium
The s-, p-, d-, and f- block elements

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
s-block
p-block
d-block
f-block
Periodic trends
Vary systemically


across a period (horizontally)
along a group (vertically)
Atomic radii
Based on probability of electron cloud,
therefore, defined by how closely an atom
lies to a neighboring atom
DECREASES to the right across a period

Due to larger nuclear attraction
INCREASES down a group

Due to more “layers” of electrons
Ionic Radii
Ions (charged atoms) form when electrons
are gained or lost….(the number of
protons and electrons don’t match!)
DECREASES to the right across a period
(in two phases)
INCREASES down a group
Ionization Energy
Defined as “amount of energy required to remove an
electron from a gaseous atom”



1st ionization energy
2nd ionization energy
Etc.
Think of this as the atom’s ability to hold onto its valence electron!
INCREASES across a period


Harder to remove ePositive energy means “harder”
DECREASES down a group

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Easier to remove eMore negative energy means “easier” or “more stable”
Element
I1
I2
I3
I4
I5
Na
490
4560
Mg
735
1445
7730
Al
580
1815
2740
11,600
Si
780
1575
3220
4350
16,100
P
1060
1890
2905
4950
6270
I6
21,200
I7
Octet Rule
Atoms tend to gain, lose, or share
electrons in order to acquire a full set of
eight valence electrons

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Note chemical stability of noble gases
Predicts ionic charge of main block elements
CATIONS—positively charged ions (lost e-)
ANIONS—negatively charged ions (gained e-)
Electron Affinity
Energy associated with adding an electron to an
atom’s electron cloud---think of the opposite of
Ionization Energy…but same effect!
INCREASES (but the energy gets more negative
= means “more stable”) across period
DECREASES (but the energy value gets more
positive = means “more difficult”) down group
Therefore, a great idea!....
Electronegativity
Indication of the relative ability of the atom
to attract electrons in a chemical bond

Think of this quantity as how strongly an atom
might want to gain an electron.
Arbitrary rating scaled to 4.0…..

Most electronegative element is fluorine with
3.98
INCREASES across a period
DECREASES down a group
Summary of Trends