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The Periodic Table. Take notes as we go. The notes are in RED and will follow your paper!. Scientists in the 1860s knew some of the chemical and physical properties of more than 60 elements.
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The Periodic Table Take notes as we go. The notes are in RED and will follow your paper!
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 thisperiodic table, Mendeleevarranged elements in rowsby 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.
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.
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. 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.
Periodic Law • The modernperiodic table organizes elements by atomic number. Whenthe elements are arranged in this way, elements that havesimilar 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. Each column of the periodic table (PT) is a group or family. There are 18 groups.
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.
Theperiodic trends in the periodic table are the result ofelectron arrangement.
Specifically, the chemical properties of each group are largely determined by the number of valence electrons.
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 toelectron 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 nolonger has an equal number of electrons and protons.Because the charges do not cancel completely, the atomhas 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. 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 commonAllelements are either metals, non metals, or metalloids.
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 are sometimes called semiconductors.
