NIS – CHEMISTRY

Lecture 27Periodic Table

Ozgur Unal

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Periodicity in Musical NotesTry to identify the periodicity in the musical notes.

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Development of the Periodic TableThe 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.

Scientists that contributed to the development of the arrangement of elements:John Newlands (1837-1898)Lothar Meyer (1830-1895)Dmitri Mendeleev (1834-1907)Henry Moseley (1887-1915)

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Development of the Periodic TableIn the late 1700s, Antoine Lavoisier (1743-1794) 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 elementsIn order to study each other’s work easily, chemists started to determine the atomic mass of elements in 1860.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

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Development of the Periodic TableIn 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.

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Development of the Periodic TableIn 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

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The Modern Periodic TableThe 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.

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The Modern Periodic Table

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The Modern Periodic TableElements are classified as metals, non-metals and metalloids.Metals:Shiny when smooth and cleanSolid at room temperatureGood conductors of electricity and heat.

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

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The Modern Periodic TableThe alkaline earth metals are in group 2.They are also highly reactive.Example: Calcium, magnesium

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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The Modern Periodic Table

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The Modern Periodic TableNon-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: FluorineExtremely unreactive group 18 elements are called noble gases.Example: Neon, Argon

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

NIS – CHEMISTRY

Lecture 28Classification of the Elements

Ozgur Unal

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Electron ConfigurationWriting 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.

The energy level of an element’s valence electrons indicates the period on the periodic table in which it is found.Example: Gallium [Ar] 4s2 3d10 4p1 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.

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The s-, p-, d- and f-Block ElementsThe periodic table is divided into sections, or blocks, according to the sublevels filled by valence electrons.

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The s-, p-, d- and f-Block Elementss-Block Elements:s-Block elements consist of groups 1 and 2. Group 1 elements have partially filled s-orbitals by valence electrons: s1 Group 2 elements have completely filled s-orbitals by valence electrons: s2

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The s-, p-, d- and f-Block Elementsp-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.

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The s-, p-, d- and f-Block Elementsd-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] 4s2 3d2

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The s-, p-, d- and f-Block Elementsf-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.

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The s-, p-, d- and f-Block ElementsExample: Strontium, which is used to produce red fireworks, has an electron configuration of [Kr] 5s2 . Without using the periodic table, determine the group, period and block of Strontium.

Strontium [Kr] 5s2 s2 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 5s2 indicates that Strontium is in period 5.