Elements, Compounds and Mixtures

Matter can be classified into three groups, elements, compounds and mixtures. 

What is an element?

An element is a pure substance that cannot be split up into two or more simpler substances.

Elements
Shiny appearance Solids at room temperature and pressure (except mercury) *Malleable  *Sonorous *Ductile High melting points and boiling point (except potassium, sodium, mercury) Good conductors of heat Good conductors of electricity	Dull appearance  Either gases, volatile liquids or solids with low melting points at room temperature Solids with low melting points at room temperature (except carbon) Brittle  Low melting points and boiling points ( except  carbon and silicon) Poor conductors of heat (except carbon in the form of diamond and graphite) Poor conductors of electricity (except carbon in the form of graphite)

Atoms and molecules

Elements are made up of tiny particles called atoms. The atoms of one element are not the same as the atoms of another element. Atoms are the smallest particles an element that have the chemical properties of that element.

Monatomic elements

Atoms are not joined together chemically. Helium, neon, argon, krypton, xenon and radon are the only elements that exist as individual atoms.

Molecule

A molecule is formed when two or more atoms chemically combined to make a group. Molecules formed by the combination of two atoms are called diatomic molecules.

Molecules consisting of three atoms are called triatomic molecules. Molecules that are formed by the combination of four or more atoms are called polyatomic molecules.

What is a compound?

 A compound is a pure substance that contains two or more elements chemically combined. It has a very different properties from the elements that from it. A compound is made up of different elements chemically combined.  It is made up of different elements chemically combined in a fixed ration. The smallest particle of a compound that can exists independently is therefore the molecule. A compound can be represented by a chemical formula.

Decomposition of compounds?
Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition. Compounds can also be broken down into elements or simpler substances by electricity.

What is a mixture?
Mixtures are formed when two substances are added together without chemical bonds being formed. Mixtures can be made up of elements and compounds. The components of a mixture are not fixed. They can be present in any ratio. 

What does a chemical formula states?

• the types of atoms (i.e elements) present in the compound
• the ratio of the different atoms present in the compound

Difference between Compounds and Elements

compounds	elements
made up of 2 or more types of atom `	made up of only one type of atom
can be broken down into 2 or more simpler substances	cannot be broken down into 2 or more simpler substances

Difference between mixtures and compounds

	Mixtures	Compounds
Separation	The components of a mixture can be separated by physical methods. (e.g. filtration, distillation or chromatography)	The elements in a compound can only be separated  by chemical reactions or by using electricity.
Properties	The chemical properties of a mixture are the same as hose of its components	The physical and chemical properties of a compound are different from those of the elements in the compound.
Energy Change	No chemical reaction takes place when a mixture is formed- usually there is little or no energy charge.	A chemical reaction takes place when a compound is formed- usually there is no energy change (e.g. heat is given out by the reactants.
Composition	The components of a mixture can be mixed in any proportion	The elements in a compound are always combined in fixed proportion.
Boiling points and melting points	Mixtures do not have a fixed boiling point and melting point.	Compound do have a fixed boiling point and melting point.

Periodic table

The elements are arranged in increasing order of proton number or atomic number as you go left from right across the table. The horizontal rows are called periods and the vertical rows are called groups. There is also a progression of metallic atoms to non-metallic atoms across each period from left to right. Group I metals are alkali metals because they react with water to form alkalis. Group II metals are called alkali earth metals because they react with water to form alkalis. They are naturally occurring as stable compounds within the earth's crust. Group VII elements are called halogens. This ter derived from Greeks halos( salt) and suffix-genes(forming), and of course means "salt former".Group VIII elements are noble gases or inert gases . The name is an allusion to the similarity unreactive Noble metals, so called due to their preciousness, resistance to corrosion and long association with the aristocracy. The block of elements (also called d-block elements) between group II and III are called transition elements or metals. Elements 58-71, elements in the Lanthanoid series are known as Lathanides or rare earth elements. These elements are found on earth in only very small amounts.  Elements 90-103 elements in the Actinoid series are known as radioactive elements. They include most of the well-known elements that are found/use in nuclear reactions.