Honors Chemistry Chapter 6 The Periodic Table

6.1 Early Attempts @ Classification: Dobereiner & Newlands � 1817 – Johann Dobereiner found Ca, Ba,

& Sr had similar props ◦ Atomic mass of Sr was ~ midway betw Ca &

Ba ◦ Grouped them into Triads �  Found several triads w/ similar props

�  In ea triad, the middle elem had an atomic mass ~ ½ way betw the other 2 elems

6.1 Early Attempts @ Classification: Dobereiner & Newlands � 1863 – John Newlands arranged elems in

order of atomic mass ◦ Noted a repetition of similar props every 8th

elem �  Called this the Law of Octaves

6.2 Mendeleev’s Periodic Table

� Dmitri Mendeleev – also put elems in a table ◦  Said props of elems were a function of their

atomic masses ◦  Felt props occurred after periods varying in

length �  7 elems in 1st 2 periods, 17 elems in next 2

6.2 Mendeleev’s Periodic Table

� Mendeleev & Lothar Meyer, working separately, made an 8 column table of elems ◦ Mendeleev left blanks in table to group all

elems w/ similar props in the same column �  Thought elems had yet to be discovered �  Predicted props & atomic masses of several elems �  Eventually discovered & his predictions were very

close

◦  Said “props of elems are a periodic function of their atomic masses” – Periodic Law

6.3 Problems w/ Mendeleev’s Table

� When all elems were placed in order of incr atomic masses, Te & I were in the wrong columns ◦  If switched, they were in correct columns

� As more elems were discovered, other pairs were also switched

6.3 Problems w/ Mendeleev’s Table

� Henry Moseley found atomic number of many elems ◦ Result – periodic law was revised:

� The properties of the elements are a periodic function of their atomic number.

6.4 Modern Periodic Table

� Atomic # gives # of p+’s & # of e-’s � Certain e- arrangements are repeated

periodically ◦  Elems w/ similar e- configs are placed in the

same column ◦ Can also list elems in the column in order of

incr principal quantum #

� This forms the Periodic Table.

Construction of Table:

� Align elems w/ similar outer e- configs ◦  1st 2 elems fill 1st energy level & 1st row of

table ◦  3rd elem ends in 2s1 – similar to H – goes

under it. ◦  Be – 2s2 – similar to He, but doesn’t fill

energy level – does not go under it ◦  B thru Ne; have e-’s in p sublevel – new

columns �  Ne fills 2nd energy level – goes under He

Construction of Table:

� Na thru Ar fill 3rd energy level, make up 3rd row

� K & Ca begin 4th energy level – start 4th row

6.5 Transition Elements

�  Sc begins to fill sublevel – starts new column

�  Sc thru Zn fill sublevel & head new columns

�  * Cr & Cu have 1 e- in highest energy level due to stability of ½ filled & completely filled sublevels

� Elements in columns 3-12 (IIIB – IIB)

6.5 Transition Elements

� Next 6 elems have e-’s in highest p sublevel ◦  Elems in column 18 have 8 e-’s in outer level

(except He) ◦ Next e- begins a new row

The Lanthanoids & Actinoids

�  - Sometimes called Rare Earth Elements � Lanthanoid Series – La thru Yb begin filling

the 4f sublevel ◦  *Assume elems have predicted configs except

for ½ filled & complete filled sublevels

� Actinoid Series – Ac thru No – fill 5f sublevel

The Lanthanoids & Actinoids

� Both series are placed below the table � Period – all elems in a horizontal row � Group – all elems in the same vertical

column

6.7 Octet Rule

� When s & p e-’s are in the highest energy level of an atom, they are in the outer level ◦  d & f e-’s can never be in outer level of

neutral atom

� ∴ the largest # of e-’s in outer level is 8 ◦ These 8 e-’s are called an Octet.

� An atom w/ 8 e-’s in outer level is considered to have a full outer level

6.7 Octet Rule � Octet Rule – an atom w/ 8 e-’s in their

outer level is chemically stable ◦ He is also considered stable bec. Its out level

is full �  Can only hold 2 e-’s

�  It is sometimes possible to force the outer level of an elem in 3rd or higher period to hold more than 8 e-’s ◦  - Extended Octet �  Noble gas comps are formed this way

Surveying the Table: Electron Configurations �  In the periodic table, elems w/ similar

props are in a column � An atom’s chemical props are determined

by its e- config ◦ ∴ the periodic table is constructed on the

basis of e- config

Surveying the Table: Electron Configurations � Elems in columns labeled “A” have their

highest energy e- in an outer s or p sublevel ◦ The coef is the same as the # of the period

Surveying the Table: Electron Configurations � Elems in columns labeled “B” have their

highest energy e- in a d sublevel, one level below the outer level ◦ The coef is 1 less than the period #

� Lanthanoids & Actinoids end in f1 – f14 w/ coef 2 less than the period #

�  Full or ½ full sublevels are more stable than other arrangements

6.9 Metals & Nonmetals

� Groups 1 & 2 contain the most active metals

� Group 1 (except H) – Alkali Metal Family � Group 2 – Alkaline Earth Metal Family

6.9 Metals & Nonmetals

� Nonmetals are on the right side of the table ◦ Group 16 – Chalcogen Family ◦ Group 17 – Halogen Family ◦ Group 18 – Noble Gases

� Metals – hard, shiny & conduct heat & electricity well

� Nonmetals – generally gases or brittle solids, dull, insulators

6.9 Metals & Nonmetals

� Elems are classified as metals or nonmetals on the basis of e- structure. ◦ Metals have few e-’s in outer level �  Tend to lose outer e-’s & form (+) ions when

forming compounds

◦ Nonmetals have more e-’s in outer level �  Gain e-’s to form (-) ions when forming comps �  May also share outer e-’s w/ other atoms

6.9 Metals & Nonmetals

� General Rule: ◦  3 or less e-’s in outer level – metals ◦  5 or more e-’s in outer level – nonmetals

� Metalloids – elems which have props of both metals & nonmetals

�  Stairstep line in table is a rough dividing line betw metals & nonmental ◦  Elems that lie along this line are usually

metalloids

6.9 Metals & Nonmetals

� Groups 13-15 include both metals & nonmetals ◦ Top of ea group is nonmetallic ◦ Metallic character of elem incr toward the

bottom of the table.

6.9 Metals & Nonmetals

� Metals are on the left side of table. � Nonmetals are on the right side of table. � Most elems are metallic. � The most unreactive atoms are the noble

gases ◦ Chemically stable bec of octet rule.