The Periodic Table

Objectives Relate the organization of periodic table to the arrangement of electrons within an atom Relate the organization of periodic table to the arrangement of electrons within an atom Explain why some atoms gain or lose electrons to form ions Explain why some atoms gain or lose electrons to form ions Determine how many protons, neutrons, and electrons an atom has, given its symbol, atomic number, & mass number Determine how many protons, neutrons, and electrons an atom has, given its symbol, atomic number, & mass number You will be able to describe how the abundance of isotopes affects an element’s average atomic mass You will be able to describe how the abundance of isotopes affects an element’s average atomic mass

History of the Periodic Table Russian chemist Dmitri Mendeleev is generally credited as being the “father” of the periodic table Russian chemist Dmitri Mendeleev is generally credited as being the “father” of the periodic table His work was based on earlier versions of periodic tables by a number of scientists, including: His work was based on earlier versions of periodic tables by a number of scientists, including: A. E. Béguyer de Chancourtois A. E. Béguyer de Chancourtois John A. R. Newlands. Lothar Meyer

History of the Periodic Table cont. The modern periodic table is based on one presented by Mendeleev in 1869 The modern periodic table is based on one presented by Mendeleev in 1869 He realized that certain properties repeat periodically when the elements are arranged horizontally in order of atomic weight He realized that certain properties repeat periodically when the elements are arranged horizontally in order of atomic weight He also placed chemically similar elements in vertical columns, leaving empty spaces as needed He also placed chemically similar elements in vertical columns, leaving empty spaces as needed From the empty spaces, Mendeleev deduced the existence of unknown elements and predicted some of their properties From the empty spaces, Mendeleev deduced the existence of unknown elements and predicted some of their properties When Mendeleev published his first table, scientists did not know about subatomic particles When Mendeleev published his first table, scientists did not know about subatomic particles

The Modern Periodic Table Today, elements are arranged by atomic number instead of by atomic weight Today, elements are arranged by atomic number instead of by atomic weight The modern periodic table has 118 elements The modern periodic table has 118 elements Only 114 have official names Only 114 have official names Many more than the 63 elements known to scientists in Mendeleev’s time Many more than the 63 elements known to scientists in Mendeleev’s time

Organization of the Periodic Table It groups similar elements together It groups similar elements together The organization makes it easier to predict the properties of elements The organization makes it easier to predict the properties of elements Elements are represented by their symbols Elements are represented by their symbols Position in the table helps to determine properties of elements Position in the table helps to determine properties of elements The order of arrangement is based on the number of protons an atom of that element has in the nucleus The order of arrangement is based on the number of protons an atom of that element has in the nucleus

Periodic Law States that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements States that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements

Transuranium Elements Are elements past uranium on the periodic table Are elements past uranium on the periodic table Have been difficult to study because they do not exist in nature. Have been difficult to study because they do not exist in nature. They must be created in a laboratory, and many exist for a very short period of time. They must be created in a laboratory, and many exist for a very short period of time. One particularly troublesome element is element 104 One particularly troublesome element is element 104 element 104 element 104 American scientists Albert Ghiorso and James Harris created this elusive element at the Lawrence Radiation Laboratory at the University of California at Berkeley in 1969 American scientists Albert Ghiorso and James Harris created this elusive element at the Lawrence Radiation Laboratory at the University of California at Berkeley in 1969

Determining Electron Arrangement You can determine how an atom’s electrons are arranged if you know where that element is located in the table You can determine how an atom’s electrons are arranged if you know where that element is located in the table A group is a column of elements in the periodic table A group is a column of elements in the periodic table Elements in the same group have the same number of valence electrons! Elements in the same group have the same number of valence electrons! Elements in the same group have similar properties Elements in the same group have similar properties Periods are the horizontal rows in the periodic table Periods are the horizontal rows in the periodic table The number of protons & the number of electrons increases as you move across a period left to right The number of protons & the number of electrons increases as you move across a period left to right

Electron Arrangement Examples Hydrogen & Helium are in the same period Hydrogen & Helium are in the same period Energy Level Orbital # of Electrons 1 s 1 1 s 1 1 s 2 1 s 2

Lithium & Carbon are in the same period Lithium & Carbon are in the same period Energy LevelOrbitalNumber of Electrons 1 s2 1 s2 2 s 1 Energy LevelOrbitalNumber of Electrons 1 s 2 1 s 2 2 s 2 2 s 2 2 p 2 2 p 2 Electron Arrangement Examples

Electron Arrangement Table

You Try!---What about oxygen? Energy Level Orbital # of Electrons

Atoms Form Ions Atoms that do not have filled outer orbitals can experience ionization Atoms that do not have filled outer orbitals can experience ionization Ionization is the ability to gain or lose valence electrons, resulting in charged atoms Ionization is the ability to gain or lose valence electrons, resulting in charged atoms Ions are charged atoms and can be positive or negative Ions are charged atoms and can be positive or negative Cations are positive ions Cations are positive ions Anions are negative ions Anions are negative ions

Specific Examples Lithium loses 1 electron to form a 1 + charged ion Lithium loses 1 electron to form a 1 + charged ion Lithium has 3 electrons Lithium has 3 electrons 1 in the outer most orbital 1 in the outer most orbital

Fluorine gains 1 electron to form a 1 - charged ion Fluorine gains 1 electron to form a 1 - charged ion It has 7 electrons in its outer orbital It has 7 electrons in its outer orbital Specific Examples

How Do the Structures of Atoms Differ? Atomic number (Z) equals the number of protons as well as the number of electrons Atomic number (Z) equals the number of protons as well as the number of electrons Atoms are always neutral! Atoms are always neutral! Mass number (A) equals the total number of subatomic particles in the nucleus Mass number (A) equals the total number of subatomic particles in the nucleus The number of protons & neutrons The number of protons & neutrons It is also the “average atomic weight” of an element It is also the “average atomic weight” of an element

Isotopes Are atoms of the same element that differ by the number of neutrons in the nucleus Are atoms of the same element that differ by the number of neutrons in the nucleus They DO NOT differ in atomic number They DO NOT differ in atomic number They ONLY differ in mass number & their physical properties They ONLY differ in mass number & their physical properties

Calculating the # of Neutrons

Let’s Practice! K Au Au B Si Si U-235 U-235 K = 20 Au = 118 B = 6 Si = 14 U-235 = 143

The Mass of an Atom Is very small Is very small We usually work with atomic mass units We usually work with atomic mass units Atomic mass unit (amu) is equal to one- twelfth of the mass of carbon-12 atom Atomic mass unit (amu) is equal to one- twelfth of the mass of carbon-12 atom Average atomic mass is a weighted average of the masses of all naturally occurring isotopes of an element Average atomic mass is a weighted average of the masses of all naturally occurring isotopes of an element The more common the isotope the greater the effect on the average The more common the isotope the greater the effect on the average

Mass of an Atoms

More Practice! Calculate the # of protons, electrons, & neutrons in the following isotopes Calculate the # of protons, electrons, & neutrons in the following isotopes 1. Carbon Nitrogen Sulfur Calcium Iodine-131