Chapter 4 The Periodic Table

Organizing the Elements Dmitri Mendeleev – Constructed the first Periodic Table in 1869 The elements were arranged according to their chemical properties Vertical columns were in order of increasing atomic mass The columns were arranged so that elements with the most similar properties were side by side

Mendeleev even left blank spaces for elements that he believed existed, but were not yet discovered, one example was… Ekasilicon… now element 32 Germanium.

Henry Moseley – in 1913 Moseley, a British physicist determined an atomic number* for each known element and arranged the Periodic Table by order of atomic number. This is the way the Periodic Table is arranged today. Periodic Law: When elements are arranged in order of increasing atomic number there is a periodic repetition of Physical and Chemical properties.

Metals Nonmetals and Metalloids Over 80% of the elements are Metal Metals are... Good Conductors of heat and electricity Metallic luster or sheen, its ability to reflect light. Malleable: Ability to be hammered into sheets or foil. Ductile: Ability to be drawn into wire. Solid @ room temp (except Hg) z Metals Nonmetals and Metalloids

Nonmetals are located in the upper right corner of the periodic table, to the right of the stair shaped line. Nonmetals have a great variation in physical properties…gases, solids, one liquid Br. Nonmetals are poor conductors, their solids are brittle.

Metalloids are located on the stair shaped line, outlined on our chart in green. Metalloids have properties of both metals and non metals. In general they… Have metallic luster Conduct electricity, but not as well as a metal, (semiconductor) Are brittle, they will shatter if hit with a hammer. They are used extensively in the electronics industry for computer chips and circuits.

Periods – the horizontal rows of the Periodic Table. Groups – the vertical columns of the Periodic Table.

Classifying the Elements Noble gases – elements in which the outermost s and p sublevels are filled. Group 18 on the chart. Representative elements – elements whose outermost s and p sublevels are only partially filled. Groups 1,2 and 13-18 on the chart (tall) Group 1 = alkali metals Group 2 = alkaline earth metals Group 17 = halogens Group 18 = noble gases

cont. 3. Transition metals – elements whose outermost s sublevel and the nearby d sublevel contain electrons (Groups 3-12) 4. Inner transition metals – elements whose outermost s sublevel and nearby f sublevel contain electrons… the two rows below the table

6.3 Periodic Trends Atomic Radius: Is one half the distance between the nuclei of two atoms of the same element when the atoms are joined. “In general, atomic size increases from top to bottom within a group and decreases from left to right across a period…” Largest in the lower left corner.

cont. Ions An Ion is an atom or group of atoms that have a positive or negative charge. Positive and negative ions form when electrons are transferred between atoms. Cations are positive ions… (generally metals) formed when atoms lose electrons to obtain the electron configuration of a noble gas. Anions are negative ions… (generally nonmetals) formed when atoms gain electrons to obtain a noble gas electron configuration.

Ionization energy Ionization energy – the energy required to overcome the attraction of the nuclear charge and remove an electron from a gaseous atom. The ionization energy decreases as you move down a group of the periodic table The ionization energy increases as you move across a period of the periodic table

Ionic Size Positive ions are smaller than the atoms they are formed from Negative ions are larger than the atoms they are formed from Ionic size tends to increase as you move down a group in the periodic table Ionic size tends to decrease as you move across a period in the periodic table

Electronegativity Electronegativity – the tendency for the atoms of the elements to attract electrons when they are chemically combined with another element Electronegativity tends to decrease as you move down a group in the periodic table Electronegativity tends to increase as you move across a period in the periodic table