Transcript Dmitri Mendeleev

Dmitri Mendeleev
• order elements by atomic mass
1834 - 1907
• saw a repeating pattern of properties
• Periodic Law – When the elements are
arranged in order of increasing relative mass,
certain sets of properties recur periodically
• used pattern to predict properties of
undiscovered elements
• where atomic mass order did not fit other
properties, he re-ordered by other properties
Periodic Table Pattern
nm H2O
a/b
H
1
H2
m Li2O m/nm BeOnm B2O3 nm CO2 nm N2O5 nm
O2 nm OF2
Li b
Be a/b B a
C a N a
O
F
7 LiH 9 BeH2 11 ( BH3)n 12 CH4 14 NH3 16 H2O 19 HF
left  right across a row (period) increasing atomic mass (not relative mass);
organized based on their activity and properties
Periodic Table Pattern
nm H2O
a/b
H
1
H2
m Li2O m/nm BeOnm B2O3 nm CO2 nm N2O5 nm
O2 nm OF2
Li b
Be a/b B a
C a N a
O
F
7 LiH 9 BeH2 11 ( BH3)n 12 CH4 14 NH3 16 H2O 19 HF
m Na2O m MgO m Al2O3 nm/m SiO2nm P4O10nm SO3 nm Cl2O7
Na b Mg b Al a/b Si a P a
S a Cl a
23 NaH24 MgH2 27 (AlH3) 28 SiH4 31 PH3 32 H2S 35.5 HCl
up  down column; similar properties; how the elements react with H and O
• some gaps were left in table for undiscovered elements; properties
of these elements were predicted.
Mendeleev's Predictions for Ekasilicon
(Germanium)
Property Silicon’s
Props
Atomic
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Mass
Color
Grey
Density
2.32
Reaction Resists
w/ Acid & Acid,
Base
Reacts
Base
Oxide
SiO2
Tin’s
Props
118
Predicted Measured
Value
Value
72
72.6
14
Si
28.09
White
metal
7.28
Grey
5.5
GreyWhite
5.4
Reacts
Acid,
Resists
Base
SnO2
Resists
Both
Resists
Both
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Ge
72.61
50
Sn
118.71
Eks1O2
GeO2
4
PERIODIC TABLE
Non-metals
Metals
Metalloids
5
PROPERTIES OF
METALS & NON-METALS
Metals
Non-metals
• Mostly solid
• Can be solid, liquid or gas
• Have shiny appearance
• Have dull appearance
• Good conductors of
heat & electricity
• Poor conductors of heat
& electricity
• Malleable & ductile
• Brittle (if solid)
• Lose electrons
• Gain or share electrons
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Metals
Non-metals
METALLOIDS
 Metalloids are elements
that possess some
properties of metals and
some of non-metals.
 The most important
metalloids are silicon (Si)
and germanium (Ge)
which are used extensively
in computer chips.
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Metalloids
Properties of Silicon
shiny
conducts electricity
brittle
PERIODIC TABLE
Metallic
Metallic character
character decreases
increases going down
acrossaagroup
period.
Least metallic
Most metallic
element
elements
F
Cs
Fr
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PERIODIC TABLE
 Seven elements exist as diatomic molecules.
 All others exist as monatomic (single atom).
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PERIODS & GROUPS

 The
Elements
periodic
in the
table
same
is composed
family have
of periods
similar (rows)
properties,
and
and areorcommonly
referred to by their traditional
groups
families (columns).
names.
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PERIODS & GROUPS
 Group
The group
Elements
Alkali
Noble
Halogens
gases
metals
2 elements
in
are
ofare
groups
metals
the
areun-reactive
most
soft
are
1-2
inmetals
called
reactive
between
and gases
13-18
alkaline-earth
that
nonmetals,
the
are
that
are
main
very
referred
aregroup
commonly
reactive.
and
metals.
to
occur
as
main-group
used
in
These
elements
nature
in
metals
light
are
only
or
bulbs.
called
are
as
representative
compounds.
less
transition
reactivewith
than
metals.
groups.
alkali
metals.
They
often
react
explosively
other
elements.
13
Important Groups - Hydrogen
• nonmetal
• colorless, diatomic gas
– very low melting point & density
• reacts with nonmetals to form molecular
compounds
– HCl is acidic gas and H2O is a liquid
• reacts with metals to form hydrides (negative
ion of hydrogen = H-)
– metal hydrides react with water to form H2
(Metal-H + H2O
H2 + metal-OH)
(NaH + HOH
H2 + NaOH)
Important Groups – IA, Alkali Metals
• hydrogen usually placed
here, though it doesn’t belong
• soft, low melting points,low
density
• flame tests  Li = red, Na =
yellow, K = violet
• very reactive, never find
uncombined in nature
• tend to form water soluble
compounds
lithium
sodium
potassium
rubidium
cesium
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Important Groups – IIA, Alkali Earth Metals
• harder, higher melting, and
denser than alkali metals
• flame tests  Ca = red, Sr =
red, Ba = yellow-green
• reactive, but less than
corresponding alkali metal
• form stable, insoluble oxides
from which they are normally
extracted
• oxides are basic = alkaline earth
• reactivity with water to form H2,
beryllium
magnesium
calcium
strontium
barium
Important Groups – VIIA, Halogens
• nonmetals
• F2 & Cl2 gases; Br2 liquid; I2
solid
• all diatomic
• very reactive
• react with metals to form ionic
compounds
• HX (X = halogen) are all acids
– HF weak < HCl < HBr < HI
fluorine
chlorine
bromine
iodine
Important Groups – VIIIA, Noble Gases
• all exist as gases at
room temperature,
– very low melting and
boiling points
• very unreactive,
practically inert
• very hard to remove
electron or add an
electron
ATOMIC
STRUCTURE
 The general designation for an atom is shown
below:
Atomic number (Z) = # of protons
Mass number (A) = # of p+ + # of n0
# of n0 = A - Z
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Charged Atoms
• The number of protons determines the
element!
– all sodium atoms have 11 protons in the
nucleus
• In a chemical change, the number of
protons in the nucleus of the atom doesn’t
change!
– no transmutation during a chemical change!!
– during radioactive and nuclear changes, atoms
do transmute
• Atoms in a compound are often electrically
charged, these are called ions
ELEMENTS
& IONS
 An ion (charged particle) can be produced when
an atom gains or loses one or more electrons.
Metals form
cations
A cation (+ ion) is formed when a
Cations are named the same as the parent atom
neutral atom loses an electron
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5.1
ELEMENTS
& IONS
 Anions are named by using the root of the
parent atom’s name and changing the ending
to –ide.
Chlorine
Non-metals
changes
to
form
anions
chloride
An anion (- ion) is formed when a
neutral atom gains an electron
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5.1
Ion Charge & the Periodic Table
•
•
•
•
Every element wants to be like the noble gases
wants 0 or 8 valence electrons
valence e- (outer electron shell used for bonding)
He has zero valence e-
ELEMENTS
& IONS
elements
of of
elements of
elements
elements
of have aof ions are
elements
of
Group
 For
main-group
elements,
the
charge
Group
VIA
Group IIA have a Group VA
Group
VIIA
have a
have
a
IA
have
a
+1
-2 charge
very characteristic
of the
group
+2 charge
-1 numbers.
charge
-3
charge
charge
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Structure of the Nucleus
(1877-1956)
• Frederick Soddy discovered that the same
element could have atoms with different masses,
which he called isotopes
– there are 2 isotopes of chlorine found in nature, one
that has a mass of about 35 amu and another that
weighs about 37 amu
• The observed mass is a weighted average of the
weights of all the naturally occurring atoms
– the atomic mass of chlorine is 35.45 amu
Isotopes
• Atomic mass - The average mass for a given element
• all isotopes of an element have the same number of
protons
• isotopes of an element have different masses
• isotopes of an element have different numbers of
neutrons
• isotopes are identified by their mass numbers
– protons + neutrons
ISOTOPES
 Atoms
Isotopesofofthe
ansame
element
element
havethat
the same
possess
atomic
a
different(Z),
number
number
but aof
different
neutrons
mass
are number
called isotopes.
(A).
The 3 isotopes of Hydrogen
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ISOTOPES &
ATOMIC MASS
 The mass of an atom is measured relative to the
mass of a chosen standard (carbon-12 atom),
and is expressed in atomic mass units (amu).
 The average atomic mass of an element is the
mass of that element’s natural occurring
isotopes weighted according to their abundance.
 Therefore the atomic mass of an element is
closest to the mass of its most abundant isotope.
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4.8 Isotopes: Natural Abundance
Isotopes of neon
Naturally occurring neon contains three different isotopes: Ne-20 (with 10
protons and 10 neutrons), Ne-21 (with 10 protons and 11 neutrons), and Ne-22
(with 10 protons and 12 neutrons).
Example 1:
Determine the number of protons, electrons and
neutrons in a chlorine atom .
35
17
Cl
A = 35
Z = 17
# of protons = 17 (Z)
# of electrons = 17 (= p+)
# of neutrons = 18 (35 - 17)
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Example 2:
Which two of the following are isotopes of each
other?
4
1
0 4
1
0
1
8
6 1
8
5
4
1
24
1
2
1
8
31
8
5
X
Y
Z
R
Isotopes of an element have the same atomic
number, but a different mass number
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Example 3:
Based on the information below, which is the most
abundant isotope of boron (atomic mass = 10.8 amu) ?
Isotope
10B
11B
Mass (amu)
10.0
11.0
Atomic mass of an element is closer to the
mass of the more abundant isotope
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CALCULATING MASS
FROM ISOTOPIC DATA
Isotope
Mass
(amu)
Abundance
(%)
107Ag
106.91
51.84
109Ag
108.90
48.16
(106.91)
(0.5184)
=o
55.42
amu
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(108.90)
(0.4816)
=e
52.45
amu
î
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107.87 amu
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Mass Number is Not the Same
as Atomic Mass
• the atomic mass is an experimental number
determined from all naturally occurring
isotopes
• the mass number refers to the number of
protons + neutrons in one isotope
– natural or man-made
THE END
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