development of spu 3

7/27/2019 Development of Spu 3

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Classification of

Elements

The Periodic Table


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Arranging the ElementsDmitri Mendeleev wanted to create a table of

elements for a textbook he was writing, arranged

the elements by increasing atomic mass.

After arranging the elements he discovered a

pattern, several properties would repeat

themselves at certain intervals.

the properties of elements are periodic

functions of their atomic masses


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Mendeleev contd

When Mendeleev arranged the elements

by increasing mass and by similar

properties there were missing spaces,elements that had yet to be found. He

predicted 6 elements and they were

found soon thereafter

6 elements he predicted were scandium,gallium, germanium, technetium,

rhenium, polonium


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Accuracy of Mendeleevs

PredictionsEkasilicon Germanium

Date predicted 1871 Date discovered 1886

Atomic mass 72 Atomic mass 72.6

Density 5.5 g/cm3 Density 5.32 g/cm3

Bonding power 4 Bonding power 4

Color Dark gray Color Grayish white


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Modern Periodic Table

Moseley determined the atomic number ofelements (based on what?)

When elements were arranged by increasing

atomic number, elements with similarproperties were grouped together withoutexception

Based on the periodic law the physical and

chemical properties of the elements areperiodic functions of their atomic number


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Periodic Table

The vertical columns of the periodic table

are groups (18). Elements in each group

have similar properties. The horizontal rows are called periods.

Elements in a period do not have similar

properties; however, the first element is

always a highly reactive solid and thelast element is an inactive gas.


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Metals

Physical properties- luster (shininess),

ductile (made into thin wires), malleable

(hammered into a thin sheet). Also goodconductors of heat and electricity.

Chemical properties- most metals react

chemically with water or oxygen which

results in corrosion of the metal.


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Nonmetals

Physical properties- dull in appearance,

very brittle. Do not conduct heat and

electricity well. Wide variety ofcharacteristics.

Chemical properties- depends on the

number of valence electrons


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Metalloids

Dividing line between the metals and the

metalloids. These have characteristics

of either or both metals and nonmetals. Boron, silicon, germanium, arsenic,

antimony, tellurium, polonium, astatine.


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Alkali Metals

Highly reactive because they have one

electron in the outermost energy level

Occur mostly in compound form Strong reducing agents

Have silvery lust, low density and low

melting point Important for diet and body maintenance


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Alkaline Earth MetalsContains 2 electrons in the outermost energy

level. Less reactive than alkali metals

Occur commonly as the carbonates,phosphates, silicates, and sulfates

React with water to form bases and hydrogengas

Calcium and magnesium are important for

diet, these elements also are used infireworks


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Boron Family

development of spu 3

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