Elements, Mixture & Compounds

Elements are found everywhere. They are the building blocks of all matter on Earth. There are over 118 different elements occurring naturally on Earth. However, some are created in a laboratory by scientists by nuclear processes.

Elements can be divided into metals and non-metals. Chemical symbols and formulae are used to represent elements and compounds.

An Element is a substance made from only one type of atom. An element cannot be broken down(chemically) into a more simple substance. The Periodic table shows all the elements

A compound is a substance formed when two or more chemical elements are chemically bonded together. Compounds can be decomposed chemically into their constituent elements. It has unique properties that are different from the properties of its individual elements. The elements in any compound are always present in fixed ratios. 

The chemical elements are divided into metals, metalloids, and non-metals.

In this chapter, we will study in detail about elements, compounds, metals,non-metals, metalloids, their properties etc.

Key Definitions

• Atom: An atom is the smallest particle of a substance which can have its own characteristic properties and cannot be split into simpler substances
• Molecule: A molecule is a larger particle formed by the chemical combination of two or more atoms. The molecule may be made from atoms of the same element, e.g. hydrogen H2, or from atoms of different elements, e.g. HCl, NaOH, held together by chemical bonds
• Element: An element is a pure substance made up of only one type of atom. Elements are further subdivided into two groups, metals and non-metals, based on their physical and chemical properties
• Pure substance: A pure substance is a homogeneous material with definite, invariable physical and chemical properties and chemical composition
• Compound: a compound consists of molecules which contain atoms of at least two different elements joined together by chemical bonds. Compounds always contain atoms of their constituent elements in the same numerical ratio

Classification of Matter

Characteristics of Elements

• An element is homogeneous in nature; it is a pure substance, made up of only one kind of atoms. For example, iron and silver are made of only iron and silver atoms.
• An element cannot be broken down into simpler substances by any physical or chemical methods such as heat, light electricity, or chemical reactions with other substances. For example, if you were to smash a piece of iron into smaller pieces or heat it, the piece still remains as the element iron.
• An atom is the smallest unit that shows all the properties of an element. For example, an atom of iron shows all the properties of that metal.
• Elements have sharp melting and boiling points. 

Classification of Elements

Properties of Metals

• Have metallic lustre.
• Are good conductors of heat and electricity.
• Are malleable and ductile.
• Are solids.
• Contain one kind of atoms. (Mono-atomic)
• Examples: Iron, Copper, Sodium, Calcium etc.
• Exceptions: 1. Zinc is nonmalleable and nonductile. 2. Mercury is a liquid metal at room temperature. 3. Tungsten is a poor conductor of electricity. 4. Sodium and Potassium are not hard. They are so soft that they can be cut easily with a knife.

Properties of Non-Metals

• Do not have lustre.
• Are bad conductors of heat and electricity.
• Are neither malleable nor ductile.
• Are solids, liquids and gases.
• Contain two kinds of atoms. (Mono-atomic or Di-atomic)
• Examples: Solid: Carbon, Silicon, Phosphorus etc. Liquid: Bromine Gas: Hydrogen, Chlorine etc.
• Exceptions: 1. Carbon fibre is ductile but not malleable. 2. Graphite is a good conductor of electricity. 3. Iodine and graphite are lustrous.

Properties of Metalloids

• Properties are midway between metals and nonmetals.
• Contain one kind of atoms. (Mono-atomic)
• Examples: Boron, Germanium, Silicon, Arsenic, Antimony, Bismuth etc.

Properties of Noble Gases

• Are gaseous in nature
• Are chemically inert.
• Occur in free state in traces in the atmosphere.
• Contain one kind of atoms. (Mono-atomic)
• Examples: Helium, Argon, Neon, Krypton, Xenon, Radon

Properties of Compounds

• A compound is homogeneous in nature, made up of the same type of molecules. 
• A compound can be broken into its constituents. 
• A compound has a fixed composition.                                                                          
• A compound has a distinct set of properties which is not similar to the properties of its constituent elements.                                                                                       
• A compound has a sharp melting and boiling point.

Mixtures are the one product of a mechanical blending or mixing of chemical substances such as elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. Despite that there are no chemical changes to its constituents, the physical properties of a mixture, such as its melting point, may differ from those of the components. Some mixtures can be separated into their components by physical (mechanical or thermal) means. 

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Key Definitions

• Mixture: A composition of two or more substances that are not chemically combined with each other and are capable of being separated. Can be homogeneous or heterogeneous
• Solution: A homogeneous mixture of two or more substances which are chemically non-reacting, whose composition can be varied within certain limits, is called a solution

Types of mixtures

1. Homogeneous Mixture – A mixture which has uniform composition and properties throughout its mass is called a homogeneous mixture. Examples: Sugar solution, salt solution etc.
2. Heterogeneous Mixture – A mixture which has different composition and properties in different parts of their mass is called a heterogeneous mixture. Examples: Sand mixed with salt, sugar in oil etc.

Solution

• Solution = Solute + Solvent
• Solute: A substance which gets dissolved in a solvent is called a solute.
• Solvent: A substance in which a solute gets dissolved is called a solvent.

Differences between solution, colloid and suspension (PACTS)

A mixture is a physical combination of two or more substances that are mixed but not chemically combined The components of a mixture maintain their own physical properties.

Mixtures are either homogeneous or heterogeneous.

The individual substances in a mixture can be separated by using different methods, depending on the type of mixture.

Let us study in this chapter, about the separation of mixtures using different methods in detail.

Separation techniques

 Use of Solvent and Filtration

• Step 1- The sand/salt mixture is stirred with water to dissolve the salt
• Step 2 and 3- The sand is filtered off and washed with pure water to remove remaining traces of salt solution. The salt solution (filtrate) is carefully heated in a dish to evaporate the water
• Pure salt crystals are obtained using water as the solvent
• Carbon and sulphur can be separated in the same method using carbon tetrachloride as the solvent

Evaporation

• This method is based on the evaporation of the liquid component in a soluble solid-liquid mixture. This method is used to obtain the coloured component of a dye from blue/black ink.
• The non-volatile solute will remain while volatile solvent will go into vapour state e.g. common salt and water

Simple Distillation

Distillation is the process of converting a liquid into vapour and then condensing it back into liquid form. Dissolved solids like salts can be removed from water by this method

Fractional Distillation

Based on the principle that different liquids have different but specific boiling points, benzene and toluene are separated by this method

Simple paper chromatography

• The process of separating dissolved constituents of a mixture by adsorption over an adsorbing material is called chromatography
• Dyes (colouring matter)in inks are separated this way

Centrifugation

• The ideal method to separate solids from a liquid in a homogeneous mixture
• Dense particles are forced to the bottom while lighter particles stay at the top when spun rapidly
• The cream is separated from milk using this technique

Separation of immiscible liquids- Separating Funnel

• Immiscible separate out in layers depending on their densities
• E.g. water + carbon tetrachloride

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