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Chapter 5

Chapter 5 . The Periodic Table. Section 5.1. In 1750, only 17 elements were known. As the rate of discovery increased, so did the need to organize the elements In 1789 Antoine Lavoisier grouped the known elements into metals, nonmetals, gases, and earths. Mendeleev’s Periodic Table.

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Chapter 5

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  1. Chapter 5 The Periodic Table

  2. Section 5.1 • In 1750, only 17 elements were known. • As the rate of discovery increased, so did the need to organize the elements • In 1789 Antoine Lavoisier grouped the known elements into metals, nonmetals, gases, and earths.

  3. Mendeleev’s Periodic Table • Medeleev made flash cards of the 63 known elements. (1863) • On each card he put the name of the element, mass, and properties. • When he lined the cards up in order of increasing mass, a pattern emerged. • Mendeleev arranged the elements into row in order of increasing mass so that elements with similar properties were in the same column. A deck of cards can be divided into four suits—diamonds, spades, hearts, and clubs. In one version of solitaire, a player must produce an arrangement in which each suit is ordered from ace to king. This arrangement is a model for Mendeleev's periodic table.

  4. Periodic Table- Arrangement of elements in columns, based on a set of properties that repeat from row to row. • Mendeleev’s Prediction • He could not make a complete table because many of the elements had not yet been discovered. He had to leave spaces for those elements. • Eka-Aluminum – one space below Al. He predicted it would be a soft metal with a low m.p. and a density of 5.9 g/cm3 • The close match between Mendeleev’s prediction and the actual properties of new elements showed how useful the periodic table could be. • Gallium was discovered in 1875. It’s a soft metal, m.p. is 29.7 ˚C, and has a density of 5.91 g/cm3 Heat from a person's hand can melt gallium. In some traffic signals, there are tiny light emitting diodes (LEDs) that contain a compound of gallium

  5. Mendeleev’s Periodic Table • How is the table organized? • Elements are arranged in order of increasing mass. • What do the long dashes represent? • They represent undiscovered elements. • Why are masses listed with some of the dashes, but not with all of them? • He was able to predict properties for some unknown elements based on the properties of neighboring elements.

  6. 5.2 The Modern Periodic Table • The sounds of musical notes that are separated by an octave are related, but they are not identical. In a similar way, elements in the same column of the periodic table are related because their properties repeat at regular intervals. But elements in different rows are not identical.

  7. Periodic Law • Mendeleev developed his chart before the proton was discovered. • In the modern periodic table, elements are arranged by increasing atomic number. (# of protons) • Periods- Each row in the table of elements is a period. • Groups- Each column on the periodic table is called a group. • Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. • Members of a group have similar chemical properties. • This pattern of repeating properties is called periodic law.

  8. Periods • Periods - the rows; represent energy levels. • Row 1 (energy level 1) 2 elements • Row 2 and 3 (energy level 2) 8 elements • Row 4 and 5 (energy level 3) 18 elements • Row 6 and 7 (energy level 4) 32 elements • The number of available orbitals increases from energy level to energy level. • Elements change from metals to metalloids to nonmetals as you move from left to right across the period.

  9. Groups • Groups/Families - the columns. • Atomic masses increase from top to bottom. • Members of a group have similar electron configurations and therefore have similar chemical properties. • Tells how many valence electrons are in the last energy level of an element.*** • Valence electrons increase from left to right on the periodic table. • Valence electrons – an electron that is in the highest occupied energy level of an atom.

  10. Valence Electrons • A valence electron is an electron that is in the highest occupied energy level of an atom. • They play a key role in chemical reactions. • The # of valence electrons increases from left to right. • Elements in a group have similar properties because they have the same number of valence electrons.

  11. Valence Electrons • Electron configuration is the arrangement of electrons in an atom. • The most stable electron configuration is one in which the outermost electron shell is completely filled. • Atoms will gain or lose electrons in order to achieve the most stable electron configuration.

  12. Atomic Mass • Atomic mass is the # protons plus the # neutrons. • It is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes. • All atoms of the same element do not have the same atomic mass. • Average atomic mass of an element is a weighted average of the masses of an elements isotopes. • The unit for atomic mass is – AMU • The standard on which the atomic mass unit is based is the mass of a Carbon-12 atom.

  13. Average Atomic Mass • Weighted Averages – some values are more important that other values • For isotopes, the one that occurs more in nature contributes more to the average atomic mass.

  14. Solving for Average Atomic Mass • When solving, • Convert the % abundance to a decimal • Multiply by its mass • Add the products together • EX: • Chlorine-35 75.78% 0.7578 X 34.969 = 26.4995 • Chlorine-37 24.22% 0.2422 X 36.966 = +8.9532 35.4527 amu You Try:

  15. Classes of Elements • 1. Chemical symbols are color coded by solids, liquids, and gases. • The symbols for solids are black. The symbols for liquids are purple. The symbols for gases are red. • 2. Elements are divided into those that occur naturally and those that do not • The symbols for elements that don’t occur naturally are white • 3. They are also classified by their general properties. • METALS, NONMETALS, METALLOIDS • In the periodic table, metals are located on the left, nonmetals are on the right, and metalloids are in between.

  16. METALS • majority of elements • good conductors of heat and electricity • most are solids at room temp. (except Hg) • most are malleable and ductile –ability to be drawn into wires • some are reactive, some are not. • Ex. Gold Ex. Mg Magnesium and aluminum are typical metals

  17. Transition Metals • The metals in groups 3-12 are called Transition Metals. • They form a bridge between the two sides of the table. They are well known for their ability to form compounds with distinctive colors. A compound of erbium (Er) and oxygen is used to tint glass pink.

  18. Nonmetals • properties are opposite of metals. • poor conductors • many are gases at room temp. • the solids tend to be brittle • Some are very reactive, some don’t react at all. • Ex. F is most reactive element. Ex. Ne is not reactive. Toothpaste contains a compound that helps to protect teeth from tooth decay. The compound is formed from the nonmetal fluorine and the metal sodium

  19. Metalloids • elements with properties that fall between those of metals and nonmetals. • Ex. A metalloid’s ability to conduct electricity can vary with temperature. Si and Ge are insulators at low temps. and conductors at high temps. • Variation Across a Period • Across a period from left to right, the elements become less metallic. From left to right across Period 3, there are three metals (Na, Mg, and Al), one metalloid (Si), and four nonmetals (P, S, Cl, and Ar). Many light bulbs are filled with argon gas.

  20. 5.3 Representative Groups • “A” groups are #1-8 • The number of the group is equal to the number of valence electrons in an atom of that element. • Valence electrons- An electron that is in the highest occupied energy level of an atom.  • Elements in a group have similar properties because they have the same number of valence electrons. • (This is why H is grouped with metals)

  21. Alkali Metals • Group 1A • Most reactive metals • Reactivity increases from the top to the bottom. • So reactive many are kept under oil to prevent reacting with water or oxygen. • One Valence Electron • Found in nature only in a compound. • Form +1 ions because they will easily give up 1 electron for stability.

  22. Alkaline Earth Metals • Group 2A • Have 2 Valence Electrons • Harder than the metals in 1A. • Form +2 Ions because they easily give up 2 electrons for stability. • Magnesium used in photosynthesis within the chlorophyll. • Calcium used in teeth and bone.

  23. Boron Family • Group 3A • Have 3 Valence electrons • Form +3 Ions because they easily give up 3 electrons for stability. • 1 metalloid (Boron) • Six metals • Aluminum is the most abundant metal in the Earth’s crust. • People are encouraged to recycle aluminum because it doesn’t take that much energy to do so.

  24. Carbon Family • Group 4A • Have 4 Valence Electrons • Form +/- 4 Ions because it will easily lose or gain 4 electrons for stability. • 1 Nonmetal (Carbon) • 2 Metalloids • 3 Metals • Metallic nature increases from top to bottom. • With the exception of water, most of the compounds in your body contain carbon. • Silicon is the second most abundant metal in the earth’s crust.

  25. Nitrogen Family • Group 5A • Have 5 Valence Electrons • Forms -3 Ions because it will easily gain 3 electrons for stability. • 2 nonmetals • 2 metalloids • 2 Metals • Nitrogen and Phosphorus are used in fertilizers.

  26. Oxygen Family • Group 6A • Have 6 Valence Electrons • Forms -2 Ions because it will easily gain 2 electrons for stability. • 3 nonmetals • 2 metalloids • 1 metal • Oxygen is the most abundant element in the Earth’s Crust. • Ozone is another from of oxygen. At ground level it can irritate your eyes and lungs. At higher levels it absorbs harmful radiation from the sun.

  27. Halogens • Group 7A • Have 7 Valence electrons • Form -1 Ions because it will easily gain 1 electron for stability. • Most reactive nonmetals increase from bottom to top. • Known as “Salt Formers” • 5 nonmetals • 1 Unknown • Fluorine is the most reactive. • React easily with most metals.

  28. Noble Gases • Group 8A • 8 Valence Electrons • Helium is the exception with only 2 valence electrons. • Extremely Un-reactive (Do not form Ions) • Odorless and colorless. • Used in light bulbs. • All are used in neon lights except argon. • Have the most stable electron configuration.

  29. Patterns on the Periodic Table • Atomic # L to R. • Atomic mass L to R. • Energy level and orbitals in rows from T to B. • (Physical Properties) metals metalloids nonmetals from L to R. • Columns atomic mass from T to B. • Columns are based on chemical properties (reactivity). • Valence Electrons from L to R. • Most reactive metals are on the left side. • Most reactive non-metals are on the right side.

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