Lecture 27 Periodic Table Ozgur Unal 1

 Try to identify the periodicity in the musical notes. 2

 The periodicity in the musical notes is similar to the one in the arrangement of the elements.  The chemical properties of elements repeat every 8th element.  This periodicity was discovered in the 19th century. 3  Scientists that contributed to the development of the arrangement of elements:  John Newlands ( )  Lothar Meyer ( )  Dmitri Mendeleev ( )  Henry Moseley ( )

 In the late 1700s, Antoine Lavoisier ( ) compiled a list of elements known at the time (33 elements).  The advent of electricity and spectrometer, new elements were discovered.  By 1870, there were around 70 known elements 4  In order to study each other’s work easily, chemists started to determine the atomic mass of elements in  In 1864, John Newlands proposed an organisational scheme for the elements.  He discovered that chemical properties of elements repeated every 8th element.  Law of octaves..  Figure 6.1

 In 1869, Meyer and Mendeleev demonstrated a connection between atomic mass and elemental properties, independently.  They arranged the elements in order of increasing mass.  Mendeleev’s table became widely accepted because it predicted undiscovered elements. 5

 In 1913, Henry Moseley discovered that atoms of each element contain a unique number of protons in their nuclei.  Moseley arranged the elements according to their atomic number.  His arrangement resulted in a clear periodic pattern of properties.  The statement that there is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number is called the periodic law.  Table 6.2 6

 The modern periodic table consists of boxes.  Each box contains an element’s name, symbol, atomic number and atomic mass.  The boxes are arranged in order of increasing atomic number.  Rows are called periods. There are 7 periods.  Columns are called groups.  Each group is numbered 1 through 18.  The elements in groups 1, 2 and 13 to 18 possess a wide range of chemical and physical properties. They are called representative elements.  The elements in groups 3 to 12 are called transition elements. 7

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 Elements are classified as metals, non-metals and metalloids. Metals:  Shiny when smooth and clean  Solid at room temperature  Good conductors of electricity and heat. 9  The group 1 elements (except for H) are known as the alkali metals.  Alkali metals are so reactive and they exist as compounds with other elements.  Example: Sodium, Li

 The alkaline earth metals are in group 2.  They are also highly reactive.  Example: Calcium, magnesium 10  The transition elements are divided into transition metals and inner transition metals.  The two sets of inner transition metals, known as lanthanide series and actinide series, are located along the bottom of the periodic table.  The rest of the elements in groups 2 t o12 make up the transition metals.  Example: Titanium

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Non-metals:  Non-metals are elements that are generally gases or brittle, dull looking solids located on the upper right side of the periodic table.  Bromine is the only non-metal liquid at room temperature.  Highly reactive group 17 elements are called halogens.  Example: Fluorine  Extremely unreactive group 18 elements are called noble gases.  Example: Neon, Argon 12

Metalloids:  Elements bordering the stairstep line in the periodic table.  Metalloids have physical and chemical properties of both metals and non-metals.  Example: Silicon, Germanium 13

Lecture 28 Classification of the Elements Ozgur Unal 14

 Writing out electron configuration using aufbau diagram can be tedious.  It is possible to determine an atom’s electron configuration and its number of valence electrons from its position on the periodic table. 15  The energy level of an element’s valence electrons indicates the period on the periodic table in which it is found.  Example: Gallium [Ar] 4s 2 3d 10 4p 1 is in period 4.  Valence electrons of the representative elements tell us the group number of those elements.  Example: Group 1 elements have 1 valence electron.

 The periodic table is divided into sections, or blocks, according to the sublevels filled by valence electrons. 16

s-Block Elements:  s-Block elements consist of groups 1 and 2.  Group 1 elements have partially filled s-orbitals by valence electrons: s 1  Group 2 elements have completely filled s-orbitals by valence electrons: s 2 17

p-Block Elements:  After s sublevel is filled, the valence electrons next occupy the p sublevel.  The p-block, comprised of groups 13 through 18, contains elements with filled or partially filled p-orbitals.  The p-block spans 6 groups because the 3 p orbitals can hold a maximum of 6 electrons.  s and p-blocks comprise the representative elements. 18

d-Block Elements:  The d-block contains the transition metals and is the largest of the blocks.  There are 10 groups in d-block, because d orbitals can have a maximum 10 electrons.  Example: Titanium [Ar] 4s 2 3d 2 19

f-Block Elements:  The d-block contains the inner transition metals.  There are 14 groups in d-block, because d orbitals can have a maximum 14 electrons.  Its elements are characterized by filled or partially filled s- orbital, and filled or partially filled 4f and 5f orbitals. 20

 Example: Strontium, which is used to produce red fireworks, has an electron configuration of [Kr] 5s 2. Without using the periodic table, determine the group, period and block of Strontium. 21  Strontium [Kr] 5s 2  s 2 indicates Strontium’s valence electrons fill s-orbital. Therefore Strontium in the s-block.  There are 2 valence electrons in 5s orbital. Therefore, Strontium is in group 2.  5 in the 5s 2 indicates that Strontium is in period 5.