Elements, Compounds And Mixtures Flashcards
What are pure substances?
Pure substances have a definite chemical composition and definite physical and chemical properties. They are all homogeneous. Elements and compounds are pure substances.
What are impure substances?
Mixtures are made up of two or more pure substances in any proportion. They do not have any definite set of properties. They may be homogenous or heterogeneous.
What are elements?
An element is a pure substance which cannot be converted into anything simpler than itself by any physical or chemical process.
How many elements are known? How many are artificial and how many are natural?
118 elements are known, out of which 92 are naturally occurring, while the rest 26 are artificially created.
Characteristics of elements
• Simplest type of pure and homogeneous substances.
• Cannot be broken down into more simpler substances.
• have a fixed melting and boiling points
• consists of only one kind of atoms
• can react chemically with other elements and compounds
to form new substances.
Classification of elements:-?
• Metals • non-metals • metalloids • noble or inert gases
There are only __ non metals known to us.
11
Define metalloids
Metalloids are elements showing some properties of metals and some properties of non metals.
Define noble gases
These are monoatomic gaseous elements which do not react chemically with other elements or compounds, so they are known as noble or inert gases. They are only 6 in number.
The most abundant element present in the earth’s crust is _____
Oxygen
Name the element which has the highest percentage in air
Nitrogen
Name two soft metals
Sodium, potassium
Example of liquid metals and nonmetals
Metals - mercury
Non metals - bromine
Example of a brittle metal
Zinc
Define atomicity
The number of atoms present in a molecule of an element is called its atomicity.
Define compound
A compound is a pure substance composed of two or more elements combined chemically in a definite proportion by mass.
Characteristics of compounds:-?
• pure homogeneous substances
•have a identical set of definite physical and chemical properties
• have definite melting and boiling points
• definite chemical formulae
• can be separated only by chemical methods
• during the formation of a compound, energy is either absorbed or liberated.
Define mixtures
Mixtures can be defined as a kind of matter which is formed by mixing two or more pure substances in any proportion, such that they do not undergo any chemical change and retain their individual properties.
Characteristics of mixtures:-?
• MIXTURE CONSISTS IF TWO OR MORE PURE SUBSTANCES THAT EXIST TOGETHER WITHOUT AHY CHEMICAL COMBINATION BETWEEN THEM.
• MAY BE HOMOGENEOUS OR HETEROGENEOUS.
• COMPONENTS OF MIXTURES VARY IN THEIR PROPORTIONS.
• THE COMPONENTS ARE LOOSELY HELD TOGETHER
• DO NOT HAVE FIXED BOILING OR MELTING POINT
• CAN BE SEPARATED BY SIMPLE PHYSICAL METHODS.
• NO ENERGY CHANGE TAKES PLACE DURING THE FORMATION OF MIXTURES
• cannot be represented by any Chemical FORMULA
what is the need for the separation of components of mixtures?
• to obtain useful substances
• to remove unwanted and harmful substances
• to obtain pure substances for preparing other useful substances.
Define solvent extraction method
The process by which a soluble solid component of a mixture is separated from an insoluble solid component by using a suitable solvent is called solvent extraction method.
Define fractional crystallisation
The process of separating two or more solids based on the difference in their solubilities in the same solvent is called fractional crystallisation.
Filtration
The process of separating insoluble solid particles from a liquid-solid mixture by allowing it to pass through a filter is called filtration.
Crystallisation
The process of formation of solid crystals from a hot super-saturated solution by cooling is called crystallisation.
