The Periodic Table Chapter 3

Introduction Mendeleev’s periodic table organised the elements on the basis of patterns of chemical properties and behaviour It also proved to be a useful tool for predicting and guiding future developments in chemistry

Why are elements periodic? Mendeleev’s periodic law: The properties of elements vary periodically with their atomic weights. It is now known that the atomic number (protons) is the essential difference between elements and the modern periodic table reflects this.

Why are elements periodic? Consider the following elements: Li 1s 2 2s 1 Na 1s 2 2s 2 2p 6 3s 1 K 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Rb 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 5s 1 Cs 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 1 What do you notice about these elements? All have one valence electron. The alkali metals all have one valence electron

Why are elements periodic? Properties that depend on valence e -s melting temperature electrical conductivity formulas of compounds formed when two or more elements react many others The valence electrons are involved in forming chemical bonds The periodic table is an arrangement of elements showing similarities in electronic configurations. The periodic table and electronic configuration

Features of the periodic table Vertical columns are called groups. Elements in the same group have the same outer-shell electronic configurations. E.g. the alkali metals (group 1) have a half-filled s-orbital (s 1 ) in their outer shell. Groups are numbered 1–18. Alkali metals, with s1 outer shells form group 1 the halogens, with s2p5 outer shells, form group 17. Horizontal rows are called periods Each period contains elements with electrons in the same outer shell (the number of shells filled) Mg 1s 2 2s 2 2p 6 3s 2 Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Both in period 3

Blocks of elements s-block group 1 (alkali metals) and group 2 (alkaline earth metals) have a half-filled or filled s-subshell or s 1 or s 2 as the highest energy subshell. p-block groups 13–18. p-subshell is the highest-energy subshell of these elements have outer-shell configurations from s 2 p 1 to s 2 p 6. Group 18 (noble gases) are unreactive as they have a full outer shell

Blocks of elements d-block transition metals located between the s- and p-blocks. the 5 orbitals (max 10 e -s ) of a d-subshell are progressively being filled. d-subshells are filled only after the s-subshell of the next shell has been filled. So.. They have outer-shell configurations from d 1 s 2 to d 10 s 2. f-block lanthanides (atomic numbers 58–71) the 7 orbitals (max 14 e -s ) in the 4f-subshell are progressively being filled actinides (atomic numbers 90–103) the 7 orbitals of the 5f-orbitals are progressively being filled. Q.1-7 p.42

Trends in the periodic table Atomic properties Radius Ionisation energy electronegativity

Atomic properties Depend on the strength of the attraction of the valence e -s and the nucleus, which depends on: The positive charge of nucleus Distance of e -s from nucleus

Atomic radius

First ionisation energy

Electronegativity

Core charge

Moving down a group: core charge is constant more e - shells. valence e -s are held less strongly. Moving across a period core charge increases valence e -s are pulled more strongly towards the nucleus. These explain the following table…..

Trends within the periodic table

Metallic and non-metallic character Elements on the right side of the table are non- metals Other elements are metals. Moving left to right across a period, elements become less metallic and show more of the properties of non-metals.

Chemical reactivity Elements on the right side of the table are non-metals Other elements are metals. Moving left to right across a period, elements become less metallic and show more of the properties of non- metals.

Reactivity of metals Down a group? …… Across a period? …….

Reactivity of non-metals Down a group? …… Q.8-10 p.48

Compounds Formed when atoms of two or more elements chemically combine in fixed proportions each compound has its own properties, which are different from those of the elements it contains. E.g. table salt (NaCl)

Compounds E.g. water (H 2 0) hydrogen and oxygen are gases under normal conditions, yet water is a liquid. If we come across an unfamiliar compound, identifying where its constituent elements are located in the periodic table gives us a good guide to its likely properties. Q p.50

Chapter 3 Review p.51 18, 20-23, 25-27, 29 Q p.50