The Periodic Table

5-1 Organizing the Elements How did Mendeleev organize the elements in his periodic table? What evidence helped verify the usefulness of Mendeleev’s table?

The Search for Order In a video store, the latest movies are usually placed on the shelves in alphabetical order but older movies are organized in a different way. Scientists faced a similar challenge when they looked for a logical way to organize the elements. The system of organization they created is one of the most useful tools in chemistry. The placement of the elements reveals the link between the atomic structure of elements and their properties.

Class Participation Opportunity Research report on the history of the periodic table Address the following questions in your report: How many elements were identified prior to 1750? What did French chemist Antoine Lavoisier do in 1789? What did Dmitri Mendeleev do that no other scientist had been able to do before? Bonus: Why is there a picture of a card game at the top of this page?

Mendeleev’s Periodic Table Mendeleev’s Proposal: arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column Mendeleev’s Prediction: could not make a complete table… left spaces… predicted the elements that would eventually fill the spaces… Evidence Supporting Mendeleev’s Table: close match between Mendeleev’s predictions and the actual properties of new elements proved how useful his table could be

5-2 The Modern Periodic Table How is the modern periodic table organized? What does the atomic mass of an element depend on? What categories are used to classify element on the periodic table? How do properties vary across a period in the periodic table?

The keyboard scale is an example of a periodic scale because it repeats at regular eight-note intervals. The notes are related but they are not identical. In the modern periodic table, elements are arranged by increasing atomic number (number of protons). Periods Period 1 has 2 elements Periods 2 and 3 have 8 elements… Groups Each column is called a group. Properties of elements repeat in a predicable 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 the periodic law. The Periodic Law

The Periodic Table What are the major differences in the layouts in Figures 6 and 7? How are the layouts alike? How will the periodic table change in the future?

Atomic Mass Four pieces of information: Atomic number, elements symbol, elements name & atomic mass Atomic Mass Units (amu): 1/12th the mass of a Carbon-12 atom (isotope) Gives scientists a convenient way to compare the masses of atoms Isotopes of Chlorine Two natural isotopes of chlorine in nature: cholorine-35 and chlorine-37; mass of chlorine-37 is greater…35.453 Weighted Averages If you add the atomic masses of the isotopes and divide by 2, you won’t get 35.453. That is because chlorine-35 occurs 75% in nature so it’s given more weight than chlorine-37. Atomic Mass

Classes of Elements Three ways to classify elements: 1. Elements are classified as solids(black), liquids(purple) or gases(red) based on their states at room temperature. 2. Naturally occurring and those that aren’t 3. Elements are classified as metals, nonmetals and metalloids.

Classes of Elements Continued Metals: Majority of elements on the periodic table Good conductors of electric current and heat Except for mercury, metals are solid at room temperature Most are malleable Many are ductile Some are extremely reactive but some do not react easily Transition Metals: In groups 3-12 Bridge the gap between metals and nonmetals Form compounds with distinctive colors Nonmetals: Poor conductors of electricity and heat Low boiling points; many are gases at room temperature Nonmetals that aren’t gases are brittle Extremely reactive and non-reactive Metalloids: properties in between metals and non metals (green boxes)

Variation Across a Period Across a period from left to right, the elements become less metallic and more nonmetallic in their properties.

5-3 Representative Groups Why do the elements in a group have similar properties? What are some properties of the A groups in the periodic table?

Valence Electrons Valence electrons are electrons 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.

The Alkali Metals The elements in Group1A are alkali metals. Single valence electron and are extremely reactive Found in nature only in compounds Table salt (compound of sodium and chlorine-sodium chloride) Reactivity of alkali metals increases from the top of Group 1A to the bottom What properties of sodium is shown in the photos? How many valence electrons does an alkali metal have?

The Alkaline Earth Metals The elements in Group 2A are called alkaline earth metals. Differences in reactivity among the alkaline earth metals are shown by the way they react with water. The Alkaline Earth Metals Magnesium and calcium have essential biological functions and they provide materials used in construction and transportation. Backpack frames, toothpaste, coral, pearl, chlorophyll molecules, plaster cast, bicycles

The Boron Family Group 3A contains boron, aluminum, gallium, indium, and thallium. Each of these has three valence electrons. Boron Glass can be made from a compound of boron, silicon and oxygen Aluminum is the most abundant metal in Earth’s crust. Packaging, window screens and frames, parts of cars and airplanes

The Carbon Family Group 4A contains a nonmetal (carbon), two metalloids (silicon and germanium) and two metals (tin and lead). Each has four valence electrons. The metallic nature of these elements increases from top to bottom. Except for water, most of the compounds in your body contain carbon, a non-metal. Silicon is the second most abundant element in Earth’s crust.

Group 5A contains two nonmetals (nitrogen and phosphorus), two metalloids (arsenic and antimony) and one metal (bismuth). The Nitrogen Family Your body uses compounds containing nitrogen and phosphorus to control reactions and release energy from food. Nitrogen Nonmetal gas Used to produce fertilizers Phosphorus Nonmetal solid Also in fertilizers Bismuth Dense metal

The Oxygen Family Oxygen Sulfur Group 6A has three nonmetals (oxygen, sulfur, and selenium), and two metalloids (tellurium and polonium). All the elements in this group have six valence electrons.. The Oxygen Family Oxygen the most abundant element in Earth’s crust Ozone is another form of the element oxygen Oxygen is needed by all complex life forms to release stored energy in food Sulfur One of the first elements discovered Found in large natural deposits

Each element in Group 7A has 7 electrons Each element in Group 7A has 7 electrons. Fluorine and chlorine are gases, bromine is a liquid that evaporates quickly and iodine is a solid that sublimes. The Halogens Despite their physical differences, the halogens have similar chemical properties. Fluorine- prevents tooth decay, nonstick coatings on pans Chlorine- kills bacteria, in bleach Iodine- needed to keep thyroid working properly, found in seafood and iodized salt

The elements in Group 8A are noble gases The elements in Group 8A are noble gases. Helium has two valence electrons but each of the other noble gases as eight valence electrons. The Noble Gases The noble gases are colorless and odorless and extremely unreactive. They were very difficult to discover. Some light bulbs are filled with argon to increase the number of hours the bulb can be lit before it burns out. All noble gases except radon are used in neon lights.