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 OrderIn 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 Periodic Law

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 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.

Classes of ElementsThree 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 ContinuedMetals: Majority of elements on the periodic table

Good conductors of electric current and heatExcept for mercury, metals are solid at room temperatureMost are malleableMany are ductileSome are extremely reactive but some do not react easily

Transition Metals: In groups 3-12Bridge the gap between metals and nonmetalsForm 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 MetalsMagnesium 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 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 Boron FamilyGroup 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 FamilyGroup 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.

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

Group 5A contains two nonmetals (nitrogen and phosphorus), two metalloids (arsenic and antimony) and one metal (bismuth).

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

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 HalogensDespite 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

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 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.

The elements in Group 8A are noble gases. Helium has two valence electrons but each of the other noble gases as eight valence electrons.