Take notes as we go. The notes are in RED and will follow your paper! The Periodic Table Take notes as we go. The notes are in RED and will follow your paper!

Unit 3, Lesson 4: Organizing the Elements

Scientists in the 1860s knew some of the chemical and physical properties of more than 60 elements. However, there was no general system of organizing the elements. To find a way to organize the elements, scientists studied the elements and the properties of the elements.

Recognizing a Pattern Dmitri Mendeleev, a Russian chemist, was one of the first scientists to design a way of organizing the elements.

Recognizing a Pattern He studied the properties of the elements and looked for patterns among the properties. He found that if the elements were listed by increasing atomic mass, certain properties appeared at certain intervals within the list.

In 1869, Mendeleev published the first periodic table of the elements In 1869, Mendeleev published the first periodic table of the elements.  In this periodic table, Mendeleev arranged elements in rows by increasing atomic mass.

He started a new row each time the chemical properties of the elements repeated. So, for any column, all of the elements in that column had similar properties.

Mendeleev was able to predict new elements. When Mendeleev arranged the elements in a list, he left gaps in the list. When he used his list to construct a table, he included these gaps in the table.

The figure below shows that he put question marks in these gaps The figure below shows that he put question marks in these gaps. The question marks indicate places where there was no known element whose properties fit the pattern.

He predicted that new elements would be discovered that would fill those gaps. He used each new element’s position in the periodic table to predict some of the properties of the element.

For example, Mendeleev left a space for an element after silicon For example, Mendeleev left a space for an element after silicon. He predicted that this element would be a gray metal that has a high melting point. In 1886, the element germanium was discovered.

As Figure 2 shows, the properties of germanium are very similar to those predicted by Mendeleev. Also discovered were two other elements that closely matched Mendeleev’s predictions: gallium and scandium.

The element mendelevium was named in his honor. Mendeleev was not the only person to develop a periodic table, but he was first to use the table to make predictions. Mendeleev is often considered to be the father of the periodic table. The element mendelevium was named in his honor.

A few elements did not fit the pattern. Mendeleev found that some elements did not quite fit the pattern. For example, he had to reverse the positions of the elements tellurium and iodine. When he did so, they were in columns with similar elements.

However, they were no longer in order of increasing atomic mass However, they were no longer in order of increasing atomic mass. Mendeleev thought that perhaps the values of the masses were not accurate, but later experiments proved that the values were correct.

Changing the Arrangement As scientists learned more about the structure of the atom, they improved Mendeleev’s table. About 40 years after Mendeleev published his table, the English chemist Henry Moseley arranged the elements by atomic number rather than by atomic mass.

As you learned earlier, an element’s atomic number is the number of protons in an atom of the element. Most elements did not change their location in the table, but a few elements did. This new arrangement fixed the discrepancies with elements such as tellurium and iodine.

Today’s periodic table includes more than 100 elements.

Periodic Law The modern periodic table organizes elements by atomic number. When the elements are arranged in this way, elements that have similar properties appear at regular intervals.

The periodic table lists the atomic number, the symbol, the name, and the average atomic mass of each element.

Elements become less metallic, less reactive, less conductive across each period. Each row of the periodic table (PT) is a period. There are seven periods.

Elements in a group have similar properties Elements in a group have similar properties. Each column of the periodic table (PT) is a group or family. There are 18 groups.

Each member of a group has similar chemical properties.

Unit 3, Lesson 5: Exploring the Periodic Table

The Role of Electrons The periodic table is organized by atomic number, which is the number of protons in an atom. For a neutral atom, the number of protons equals the number of electrons.  

 The periodic trends in the periodic table are the result of electron arrangement.

Specifically, the chemical properties of each group are largely determined by the number of valence electrons.

Valence electrons account for similar properties.

The diagrams in show atoms of two elements from Group 1: lithium and sodium. Because they each have one valence electron, lithium and sodium have similar chemical properties.

An element’s location in the periodic table is related to electron arrangement.

A hydrogen and lithium atom has one electron in it’s outermost shell and a helium atom has two electrons in its outermost shell.

Ion Formation Atoms whose outermost orbitals are not filled may undergo a process called ionization. That is, such atoms may gain or lose valence electrons so that they have a filled outermost shell.    

A charged atom is called an ion. If an atom gains or loses electrons, it no longer has an equal number of electrons and protons. Because the charges do not cancel completely, the atom has a net electric charge.

Group 1 – 13: elements that form positive ions. They do so by losing electrons and becoming more positive and becoming cations.

Group 15 - 17: elements that form negative ions. They do so by gaining electrons and becoming more negative and becoming anions.

Group 14: elements that can form positive OR negative ions Group 14: elements that can form positive OR negative ions. It just depends on what they are bonding with.

How Are Elements Classified? As you have learned, elements within a group have similar chemical properties. In addition to being organized into groups, the elements in the 18 groups in the periodic table are further classified into three main categories.

These three categories are based on general properties that the elements in the categories have in common  All elements are either metals, non metals, or metalloids.

Metals: Most metals are shiny solids that can be stretched and shaped Metals: Most metals are shiny solids that can be stretched and shaped. They are also good conductors of heat and electricity. Most of the elements are metals.

Nonmetals: except for hydrogen, are found on the right side of the periodic table. They may be solids, liquids, or gases. Solid nonmetals are often dull and brittle. They are poor conductors of heat and electricity.

Metalloids: Can conduct electricity under certain conditions Metalloids: Can conduct electricity under certain conditions. Metalloids are sometimes called semiconductors.

Metalloids

Unit 3, Lesson 6: Families of Elements

Sometimes, one or more groups in the periodic table are categorized as being members of a unit called a family. Members of a family in the periodic table have properties in common.

You learned yesterday that elements can be classified as metals, nonmetals, and semiconductors. Elements are further categorized into five families.  The elements in a family have the same number of valence electrons. Today we will explore some of the shared physical and chemical properties of elements in each family.

Alkali Metals All the metals in Group 1 (NO Hydrogen) The alkali metals are very reactive. They are soft and shiny React violently with water. They are found combined with other elements in the form of compounds – never alone.

Alkaline Earth Metals Group 2 Harder, denser, stronger, and have higher melting points than alkali metals. These metals form compounds that are found in limestone and in the human body.

Transition Metals Groups 3–12 of the periodic table. harder, more dense, and have higher melting points than alkali metals and alkaline-earth metals.

Noble Gases Group 18 relatively nonreactive (inert) exist as single atoms instead of as molecules Full set of valence electrons so will not lose or gain electrons

Halogens Group 17 most reactive nonmetals. Sometimes called SALTS

Carbon Family member of Group 14 Forms many compounds

Nitrogen Elements in Group 15 2 members

Oxygen Family Elements in Group 16 3 members

Metalloids Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium is still undecided whether to join the group Semiconductors – depends on situation

Post-Transition Metals All the other metals Just a little less reactive, less shiny, less conductive than transition metals

Hydrogen Hydrogen is in a class all by itself. Does not behave like any of the other elements. Hydrogen is the most abundant element in the universe. 75% of all atoms in the universe are hydrogen atoms.

Synthetic Elements Made in a lab All elements that have atomic numbers greater than 92 Radioactive