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Dmitri Mendeleev
• order elements by atomic mass• 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
1834 - 1907
Periodic Table Pattern
H
nm H2O a/b
1 H2
Lim Li2O
b
7 LiH
Bem/nm BeO
a/b
9 BeH2
nm B2O3
a
11 ( BH3)n
Bnm CO2
a
12 CH4
Cnm N2O5
a
14 NH3
Nnm O2
16 H2O
Onm OF2
19 HF
F
left right across a row (period) increasing atomic mass (not relative mass);
organized based on their activity and properties
H
nm H2O a/b
1 H2
Lim Li2O
b
7 LiH
Nam Na2O
b
23 NaH
Bem/nm BeO
a/b
9 BeH2
m MgO
b
24 MgH2
Mg
nm B2O3
a
11 ( BH3)n
B
m Al2O3
a/b
27 (AlH3)
Al
nm CO2
a
12 CH4
C
nm/m SiO2
a
28 SiH4
Si
nm N2O5
a
14 NH3
N
nm P4O10
a
31 PH3
P
nm O2
16 H2O
O
nm SO3
a
32 H2S
Snm Cl2O7
a
35.5 HCl
Cl
nm OF2
19 HF
F
Periodic Table Pattern
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.
4
Mendeleev's Predictions for Ekasilicon (Germanium)
Property Silicon’s Props
Tin’s Props
Predicted Value
Measured Value
Atomic Mass
28 118 72 72.6
Color Grey White metal
Grey Grey- White
Density 2.32 7.28 5.5 5.4
Reaction w/ Acid &
Base
Resists Acid, Reacts Base
Reacts Acid,
Resists Base
Resists Both
Resists Both
Oxide SiO2 SnO2 Eks1O2 GeO2
32
72.61
Ge
14
28.09
Si
Sn 50
118.71
5
PERIODIC TABLE
Metals Non-metals
Metalloids
6
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
Metals Non-metals
8
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.
Metalloids
Properties of Siliconshiny
conducts electricitybrittle
10
PERIODIC TABLE
Metallic character increases going down a groupMetallic character decreases going across a period.
Cs
Fr
Most metallic elements F
Least metallic element
11
PERIODIC TABLE
Seven elements exist as diatomic molecules. All others exist as monatomic (single atom).
12
PERIODS & GROUPS
The periodic table is composed of periods (rows) and groups or families (columns).
Elements in the same family have similar properties, and are commonly referred to by their traditional names.
13
PERIODS & GROUPS
Elements in groups 1-2 and 13-18 are referred to as main-group or representative groups.
Alkali metals are soft metals that are very reactive. They often react explosively with other elements.
Noble gases are un-reactive gases that are commonly used in light bulbs.
Halogens are the most reactive nonmetals, and occur in nature only as compounds.
Group 2 elements are called alkaline-earth metals. These metals are less reactive than alkali metals.
The group of metals in between the main group elements are called transition metals.
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)
15
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
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,
magnesium
calcium
beryllium
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
bromine
iodine
chlorine
fluorine
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
19
ATOMICSTRUCTURE
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
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
21
5.1
ELEMENTS& IONS
An ion (charged particle) can be produced when an atom gains or loses one or more electrons.
A cation (+ ion) is formed when a neutral atom loses an electron
Metals form cations
Cations are named the same as the parent atom
22
5.1
ELEMENTS& IONS
An anion (- ion) is formed when a neutral atom gains an electron
Non-metals form anions
Anions are named by using the root of the parent atom’s name and changing the ending to –ide.
Chlorine changes to chloride
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-
24
elements of Group IIA have a
+2 charge
elements of Group IA have a +1
charge
elements of Group VA have a
-3 charge
elements of Group VIA have a
-2 charge
elements of Group VIIA have a
-1 charge
ELEMENTS& IONS
For main-group elements, the charge of ions are very characteristic of the group numbers.
Structure of the Nucleus
• 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
(1877-1956)
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
27
ISOTOPES
Atoms of the same element that possess a different number of neutrons are called isotopes.
Isotopes of an element have the same atomic number (Z), but a different mass number (A).
The 3 isotopes of Hydrogen
28
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.
4.8 Isotopes: Natural AbundanceIsotopes 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).
30
Example 1:
Determine the number of protons, electrons and neutrons in a chlorine atom .
3517Cl
A = 35
Z = 17
# of protons = 17 (Z)
# of electrons = 17 (= p+)
# of neutrons = 18 (35 - 17)
31
Example 2:
Which two of the following are isotopes of each other?
410 410 412 412186 185 183 185X Y Z R
Isotopes of an element have the same atomic number, but a different mass number
32
Example 3:
Based on the information below, which is the most abundant isotope of boron (atomic mass = 10.8 amu) ?
Atomic mass of an element is closer to the mass of the more abundant isotope
Isotope 10B 11B
Mass (amu) 10.0 11.0
33
(106.91) (0.5184) = 55.42 amu
(108.90) (0.4816) = 52.45 amu
107.87 amu
IsotopeMass
(amu)Abundance
(%)
107Ag 106.91 51.84
109Ag 108.90 48.16
CALCULATING MASSFROM ISOTOPIC DATA
Atomic mass Abundance Mass of Abundance Mass ofx + x
of an element of isotope 1 isotope 1 of isotope 2 isotope 2
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Mass Number is Not the Sameas 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
35
THE END