Elements as Substances

Elements are pure substances that consist of only one type of atom. They cannot be broken down into simpler substances by chemical means.
The periodic table lists all the known elements. They are arranged according to their atomic number i.e., the number of protons in an atom of the element.
Elements are grouped into ‘groups’ (vertical columns) and ‘periods’ (horizontal rows). Elements in the same group have similar properties because they have the same number of electrons in their outer shell.
Elements can be classified as metals, non-metals, and metalloids. Metals are generally shiny, good conductors of heat and electricity, and ductile. Non-metals are generally dull, poor conductors of heat and electricity, and brittle. Metalloids have properties of both metals and non-metals.
Some elements occur naturally on Earth, while others can only be created in a laboratory.
Elements can combine with each other to form compounds, which have different properties from the elements that make them up.
Symbols are used to represent elements. These symbols consist of one or two letters, with the first letter always capitalised.
Each element has a unique set of properties, including melting point, boiling point, density, reactivity, and atomic structure.
Isotopes are atoms of the same element that have different numbers of neutrons. Despite this, they have identical chemical properties to other atoms of the same element because chemical properties are determined by the number of electrons, which is the same for all atoms of a given element.
Elements in Group 1 of the periodic table are called alkali metals and are highly reactive due to the single electron in their outer shell.
The noble gases are in Group 8 or 0 of the periodic table. These elements are unreactive as they have a full outer shell of electrons.