elements and the periodic table. patterns of elements - the periodic table during the 19th century,...

Elements and the Periodic Table

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Patterns of Elements - The Periodic Table

During the 19th century, chemists identified families of similar elements (e.g. chlorine, bromine and iodine). This led chemists to search for a pattern in the properties of all elements.

In 1869, Mendeleev found a pattern in the properties of elements and their relative atomic masses, which he summarized in a table. In time, Mendeleev’s table of elements led to the modern Periodic Table.

Patterns of Elements - The Periodic Table

The modern Periodic Table shows that the properties of elements are closely related to their atomic number. Elements with similar properties fall in the same vertical column in the Periodic Table.

These vertical columns of similar elements are called groups.

The horizontal rows are called periods.

Blocks of Similar Elements

The Periodic Table can be divided into four blocks of similar elements:

• Reactive metals in Groups 1 and 2.

• Ordinary, useful metals including transition metals in the center of the Periodic Table.

• Non-metals in Groups 3 to 7 above the steps separating metals from non-metals.

• Noble gases in Group O.

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The Alkali Metals in Group 1:

Are reactive metals with similar properties.

Have lower melting points, lower boiling points, lower densities and are softer than other metals.

React rapidly with oxygen in the air to form oxides.

Become more reactive with increase in relative atomic mass.

All the alkali metal atoms have one electron in their outer shell (e.g. Na 2,8,1). When they react, they lose this outermost electron to form stable ions with filled shells and one positive charge (e.g. Na 2,8).

Alkaline Earth Metals Group 2

• Two electrons in the outer shell• Low electron affinities• Low electro-negativities• High in the reactivity series of metals,

but not as high as the alkali metals of Group 1.

• Elements are all metals with a shiny, silvery-white color.

• Are harder and denser than sodium and potassium, and have higher melting points.

• The last element, radium, is radioactive.

The Transition Metals - Groups 3 - 12

Have similar properties.

Have high melting points, high boiling points and high densities.

Are unreactive with cold water.

Form more than one stable ion (e.g. copper forms Cu+ and Cu2+ ions).

Have colored compounds.

Can act as catalysts both as elements and in their compounds (e.g. Fe or Fe2O3 is a catalyst for the Haber process).

Metals in Mixed Groups 13-16

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Special Note About Bonding

Metals tend to lose electrons and nonmetals tend to gain electrons, metals and nonmetals like to form compounds with each other. These compounds are called ionic compounds.

When two or more nonmetals bond with each other, they form a covalent compound.

Metalloids

• Elements on both sides of the zigzag line have properties of both metals and nonmetals. These elements are called metalloids.

Physical Properties of Metalloids:

• Solids• Can be shiny or dull• Ductile• Malleable• Conduct heat and electricity

better than nonmetals but not as well as metals.

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Nonmetals

Nonmetals are found to the right of the stair-step line. Their characteristics are opposite those of metals.

Physical Properties of Nonmetals:• No luster (dull appearance)• Poor conductor of heat and electricity• Brittle (breaks easily)• Not ductile• Not malleable• Low density• Low melting point

Chemical Properties of Nonmetals:• Tend to gain electrons

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Lanthanides

• Silvery-white metals that tarnish when exposed to air, forming their oxides.

• Relatively soft metals. Hardness increases somewhat with higher atomic number.

• High melting points and boiling points.

• Very reactive.

• Burn easily in air

• Their compounds are generally ionic.

• The lanthanides react readily with most nonmetals and form binaries on heating with most nonmetals.

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Actinides

All are radioactive.

Actinides are highly electropositive.

The metals tarnish readily in air.

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Actinides are very dense metals with distinctive structures. Numerous allotropes may be formed (plutonium has at least 6 allotropes!).

They react with boiling water or dilute acid to release hydrogen gas.

Actinides combine directly with most nonmetals.

The Halogens - Group 17: Are reactive non-metals with similar properties.

Form diatomic molecules (e.g. Cl2, F2, Br2, I2)

Have low melting points and low boiling points.

Change from gases (F2 and Cl2), to liquid (Br2), to solid (I2) with increase in relative atomic mass.

Become less reactive with increase in relative atomic mass.

All the halogen atoms have seven electrons in their outer shell (e.g. Cl 2,8,7).

When they react, they try to gain another electron in order to have eight electrons in their outermost shell which is far more stable (e.g. Cl- 2,8,8)

The Noble Gases - Group 18

Are very unreactive non-metals with similar properties.

Form monatomic molecules with one atom (e.g. He, Ne, Ar).

Have very low melting points and very low boiling points.

Are all gases at room temperature.

All the noble gas atoms have stable electron structures with eight electrons in their outer shell, except helium atoms which have a very stable single shell with two electrons.

Boron Family Group 13

• 5: B Boron 10.81g

• 13: Al Aluminum 26.981g

• 31: Ga Gallium 69.72g

• 49: In Indium 114.82g

• 81: Tl Thallium 204.37g

• 113: detected summer of 2003(2003)

Carbon Family Group 14

• 6: C Carbon 12.011g

• 14: Si Silicon 28.0855g

• 32: Ge Germanium 72.59g

• 50: Sn Tin 118.69g

• 82: Pb Lead 207.2g

• 114: Uuq Ununquadium

Nitrogen Family Group 15

• 7: N Nitrogen 14.0067g

• 15: P Phosphorus 30.9738g

• 33: As Arsenic 74.9216g

• 51: Sb Antimony 121.75g

• 83: Bi Bismuth 208.9806g

Oxygen Family Group 16

• 8: O Oxygen 15.9994g

• 16: S Sulfur 32.06g

• 34: Se Selenium 78.96g

• 52: Te Tellurium 127.60g

• 84: Po Polonium (208.9824)

Halogens Group 17

• 1: H Hydrogen 1.008g

• 9: F Fluorine 18.9984g

• 17: Cl Chlorine 35.453g

• 35: Br Bromine 79.904g

• 53: I Iodine 126.9045g

• 85: At Astatine (209.9871)

Inert (Noble) Gases Group 18

• 2: He Helium 4.00260g

• 10: Ne Neon 20.179g

• 18: Ar Argon 39.948g

• 36: Kr Krypton 83.80g

• 54: Xe Xenon 131.30g

• 86: Rn Radon (222.0176)

Elements From Stardust

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Above, The Dumbbell nebula, consisting of very rarefied gas that has been ejected from the hot central star (visible on this image), in one of its last evolutionary stagesImage courtesy of ESO

Right, Nucleogenesis in stars Image courtesy of Mark Tiele Westra

Hydrogen is converted into helium.

Hydrogen is depleted in the center of the star, Star evolves, becoming larger, cooler, and redder- a red giant.

After a brief phase, the temperature and density in the core increase - new reactions occur.

Helium than starts to burn. Two helium nuclei can fuse to form a beryllium nucleus. (nuclei are unstable, and most will rapidly disintegrate)

Some helium nuclei will collide with another helium nucleus, forming carbon - three helium nuclei form a carbon nucleus.

Nucleogenesis in Stars

Nucleogenesis in Stars

A fraction of the carbon nuclei thus formed collide with further helium nuclei to form oxygen. In the cores of giant stars, helium is converted to a mixture of carbon and oxygen.

Once this carbon-oxygen core has formed, the star ejects its outer envelope in the form of a planetary nebula, leaving behind a white dwarf.

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This Power Point presentation was constructed and is copyrighted by Roger Price 7/08