University:
University of Alberta
Course:
CHEM 101 | Introductory University Chemistry I
Academic year:

2024
Views:

427

Pages:

7
Author:

Neena N.

PERIODIC TABLE Organisation The periodic table is a tool used by chemists to organise the elements and the large amount of chemical information for each element. The elements in the periodic table are arranged in increasing atomic number. Features of the periodic table 1. Elements in the same horizontal row are said to be in the same period. Elements in the same period, have the same number of electron shells occupied. 2. Elements in the same vertical column are said to be in the same group. Elements in the same group have the same number of electrons in their outer shell. 3. Elements are spilt into metals and non- metals. About 80% of the elements are metals. 15% are non metals and the rest are metalloids, which have properties of both metals and non-metals. The metals are on the left hand side of the table and in the middle and the non-metals are on the right hand side. Chemists can use the group and period of an element to work out the electron configuration of the element. Similarly, chemists can use the electron configuration to work out the properties of an element. Therefore the periodic table is a very useful tool for chemists and chemistry students. Groups A vertical column of the elements in the periodic table. Elements in the same group display similar chemical properties as they have the same number of electrons in the outer shell. The group gives you the number of valence shell electrons. Example: Group 1 elements and their respective electron configurations The table above shows the first 4 elements in Group 1. They all have one electron in their outer shell. Groups in the periodic table are given names: Most elements are solids at room temperature (25 °C). Two are liquids: mercury and bromine. Ten are gases, which include the noble gases (group 18). Alkali metals The alkali metals are the Group 1 elements. They include: Hydrogen is usually placed in group 1, as it has one electron in its outer (and only shell), but it is not a metal. Reactivity of alkali metals: They all react readily with non-metals to form compounds such as sodium chloride and calcium chloride. The Halogens The halogens are the Group 17 elements. The halogens all react readily with metals to form compounds such as sodium chloride and calcium chloride. They include: The Noble Gases The Noble gases are the Group 18 elements. At room temperature, the noble gases are unreactive, as they have a full outer shell of electrons. They include: Period A horizontal row in the periodic table. Elements in the same period have the same number of shells that contain electrons. Example: Elements in period 3 will all have 3 shells occupied with electrons. From the above it can be seen shells 1 and 2 are complete and the third shell has a varying number of electrons. Each of these elements is in a different group in the periodic table, so has a different number of electrons in their outer shell. Blocks The periodic table is further arranged into four blocks which are associated with the four atomic sub-levels. • The s-block consists of group 1 and 2 elements (including H & He) • The p-block contains group 13-18 elements • The d-block contains group 3-12 elements (the transition metals) • The f-block contains the lanthanoids and the actinoids Knowing the blocks of periodic table makes building electron configurations much simpler!