The Periodic Table and Periodic Trends CH 6 The Periodic Table and Periodic Trends

Organizing the Elements Mendeleev arranged the elements in his periodic table in order of increasing atomic mass 1869

The Periodic Law When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

Periods and Groups Periods – rows on a periodic table Groups – columns on a periodic table

The Periodic Table Displays symbols and names of the elements Information about the structure of the atom Average atomic mass Atomic number

Metals Good conductors of electricity and heat Luster Ductile Malleable

Nonmetals Poor conductors of heat and electricity Brittle Varies in states (solids, liquids, gases)

Metalloids Along the stair-step Properties similar to those of metals and nonmetals Conduct heat and electricity somewhat

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Important Regions Alkali metals – Group 1A Alkaline earth metal – Group 2A Halogens – Group 7A Noble gases – Group 8A Transition metals Inner Transition metals Lanthanides Actinides

Electron Configurations in Groups Elements can be sorted into noble gases, representative elements, transition metals, inner transition metals based on their electron configurations Every element ends in the same last term in the electron configuration

Representative Elements Groups 1,2,13,14,15,16,17 Called representative elements because they display a wide range of physical and chemical properties

Transition Elements In atoms of a transition metal, the highest occupied s sublevel and a nearby d sublevel contain electrons. These elements are characterized by the presence of electrons in the d orbitals Inner transition elements contain unfilled f orbitals

Periodic Trends Atomic radius – ½ the distance between the nuclei of two atoms of the same element when the atoms are joined Extremely small – measured in picometers Atomic size (radius) increases from top to bottom within a group and decreases from left to right across a period.

Periodic Trends Atomic radius – WHY??? Group trends – as the atomic number increases within a group, the charge on the nucleus increases and the number of occupied energy levels increases. The increase in positive charge draws the electrons closer to the nucleus The increase in the number of occupied orbitals shields the electrons in the highest occupied energy level from the attraction of the protons in the nucleus.

Periodic Trends Atomic Size – WHY???? Periodic trends – each element has one more proton and one more electron that then preceding element. Across a period, the electrons are added to the same principal energy level. The shielding effect is constant for all the elements in a period The increasing nuclear charge pulls the electrons in the highest occupied energy level closer to the nucleus and the atomic size decreases

Ions Positive and negative ions form when electrons are transferred between atoms\ Metals form cations – they lose electrons to form a positive charge Nonmetals form anions – they gain electrons to form a negative charge

Periodic Trends Ionization Energy – the energy required to remove an electron from an atom Measured in the gaseous state The energy required to remove the first electron – first ionization energy The energy required to remove the second electron – second ionization energy The energy required to remove the third electron – third ionization energy

Periodic Trends Ionization Energy Can help you predict what ions will form The first ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period

Periodic Trends Ionization Energy – WHY???? Atomic size increases as the atomic number increases within a group. As the size of the atom increases, nuclear charge has a smaller effect on the electrons in the highest occupied energy level. So less energy is required to remove an electron

Periodic Trends Ionization Energy – WHY???? The nuclear charge increases across the period, but the shielding effect remains constant. So there is an increase in the attraction of the nucleus for an electron. Thus, it takes more energy to remove an electron from an atom

Periodic Trends Ionic Size Cations are always smaller than the atoms from which they form Anions are always larger than the atoms from which they form

Periodic Trends Electronegativity – the ability of an atom of an element to attract electrons when the atom is in a compound

Periodic Trends Electronegativity – decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period Metals have low values Nonmetals have higher values Fluorine – highest with value of 4

Summary of Trends