1. Chemical Reactions

What is a Chemical Reaction?

A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in order to form a new substance

A burning candle is the best example of physical and chemical change. Take a candle and light it. As time passes, we can observe that the candle changes to wax. If you cover the candle with a jar, it will extinguish.

In the demonstration, burning of the candle is a chemical change while conversion of the candle to wax is a physical change. In a physical change, there is basically a change of state of the substance but in the case of a chemical change mostly a new substance is formed in which either energy is given off or absorbed. Thus, we can conclude that chemical changes are accompanied by certain physical changes.

Basic Concepts of Chemical Reactions

• A Chemical Reaction is a process that occurs when two or more molecules interact to form a new product(s).
• Compounds that interact to produce new compounds are called reactants whereas the newly formed compounds are called products.
• Chemical reactions play an integral role in different industries, customs and even in our daily life. They are continuously happening in our general surroundings; for example, rusting of iron, pottery, fermentation of wine and so on.
• In a chemical reaction, a chemical change must occur which is generally observed with physical changes like precipitation, heat production, colour change etc.
• A reaction can take place between two atoms or ions or molecules, and they form a new bond and no atom is destroyed or created but a new product is formed from reactants.
• The rate of reaction depends on and is affected by factors like pressure, temperature, the concentration of reactants.

Chemical Equations

Due to the vast amounts of chemical reactions happening around us, a nomenclature was developed to simplify how we express a chemical reaction in the form of a chemical equation. A chemical equation is nothing but a mathematical statement which symbolizes the product formation from reactants while stating certain condition for which how the reaction has been conducted.

The reactants are on the left-hand side whereas products formed on the right-hand side connected by a one-headed or two-headed arrows. For example, a reaction

A + B → C + D

Here, A and B are the reactants, which react to form the products C and D.  In an actual chemical equation, reactants are denoted by their chemical formula. In order to assure the law of conservation of mass, a chemical equation must be balanced i.e. the number of atoms on both sides must be equal. This is the balancing of the equation.

Let us consider an actual chemical reaction between Methane(CH₄) and Oxygen (O₂),

Here we can see how the number of each atom on the left side is balanced on the right side, as stated by the law of conservation of mass.

Types of Chemical Reactions

The basis for different types of reactions is the product formed, the changes that occur, the reactants involved and so on. Different types of reactions are

• Combustion reaction
• Decomposition reaction
• Neutralization reaction
• Redox Reaction
• Precipitation or Double-Displacement Reaction
• Synthesis reaction

1. Combustion Reaction

A combustion reaction is a reaction with a combustible material with an oxidizer to give an oxidized product. An oxidizer is a chemical a fuel requires to burn, generally oxygen. Consider the example of combustion of magnesium metal.

2Mg+O2→2MgO+Heat

Here, 2 magnesium atoms react with a molecule of oxygen producing 2 molecules of the compound magnesium oxide releasing some heat in the process.

2. Decomposition Reaction

A Decomposition reaction is a reaction in which a single component breaks down into multiple products. Certain changes in energy in the environment have to be made like heat, light or electricity breaking bonds of the compound. Consider the example of the decomposition of calcium carbonate giving out CaO (Quick Lime) which is a major component of cement.

CaCO3(s)→HeatCaO(s)+CO2(g)

Here, the compound Calcium carbonate when heated breaks down into Calcium Oxide and Carbon Dioxide.

3. Neutralization Reaction

A Neutralization reaction is basically the reaction between an acid and a base giving salt and water as the products. The water molecule formed is by the combination of OH^– ions and H⁺ ions. The overall pH of the products when a strong acid and a strong base undergo a neutralization reaction will be 7. Consider the example of the neutralization reaction between Hydrochloric acid and Sodium Hydroxide giving out sodium chloride(Common Salt) and water.

HCl+NaOH→NaCl+H2O

Here, an acid and a base, Hydrochloric acid and Sodium Hydroxide react in a neutralization reaction to produce Sodium Chloride(Common Salt) and water as the products.

4. Redox Reaction

A REDuction-OXidation reaction is a reaction in which there is a transfer of electrons between chemical species. Let us consider the example of an electrochemical cell-like redox reaction between Zinc and Hydrogen.

Zn+2H+→Zn2++H2

Here, A Zinc atom reacts with 2 ions of positively charged hydrogen to which electrons get transferred from zinc atom and hydrogen becomes a stable molecule and Zinc ion is the product.

5. Precipitation or Double-Displacement Reaction

It is a type of displacement reaction in which two compounds react and consequently, their anions and cations switch places forming two new products. Consider the example of the reaction between silver nitrate and sodium chloride. The products will be silver chloride and sodium nitrate after the double-displacement reaction.

AgNO3+NaCl→AgCl+NaNO3

Here, Silver Nitrate and Sodium Chloride undergo a double displacement reaction. Wherein Silver replaces Sodium in Sodium Chloride and Sodium joins with Nitrate becoming Sodium Nitrate along with the Silver Chloride as the product.

6. Synthesis Reaction

A Synthesis reaction is one of the most basic types of reaction wherein multiple simple compounds combine under certain physical conditions giving out a complex product. The product will always be a compound. Let us consider the Synthesis reaction of sodium chloride with reactants solid sodium and chloride gas.

2Na(s)+Cl(g)→2NaCl(s)

Here, we have 2 Atoms of solid Sodium reacting with Chlorine gas giving out Sodium Chloride viz. Common Salt as the product.

2. Metals and Nonmetals

Difference Between Metals And Nonmetals

Metals and Nonmetals are different types of materials present around us. Elements can be divided into metals and nonmetals and it is important to know whether a particular element is a metal or nonmetal. Metals (like copper and aluminium) are good conductors of heat and electricity, while nonmetals (such as phosphorus and sulfur) are insulators. Materials are distinguished as above, based on their properties.

What are Metals?

Majority elements in the periodic table are metals. This includes alkali metals, transition metals, lanthanides, actinides and alkaline earth metals. Metals are separated by nonmetals on a periodic table through a zigzag line starting from carbon, till radon. The elements between the two are phosphorus, selenium and iodine.

These elements and elements right to them in the periodic table are nonmetals. Elements present just to the left of the line are termed as semimetals or metalloids. These will have the combined properties of both metals and nonmetals.

Non-metals occupy the upper right-hand portion of the periodic table. Considering the properties of non-metals it is not shiny, malleable or ductile nor are they good conductors of electricity. These properties of non-metals provide one means by which we can distinguish metals from non-metals.

Properties of Non-metals have less in common with each other than metals. Their physical and chemical properties vary widely. Some non-metals are solids and some are gases at room temperature.

What are Non metals?

Very few elements in the periodic table are non-metals. These are present on the right-hand side in the periodic table. Elements that come under non-metals are sulphur, carbon, all halogens, phosphorus, hydrogen, oxygen, selenium, nitrogen and noble gases.

In the periodic table, non-metals are located left of the halogens and to the right of the metalloids. Since noble gases and halogens are also non-metals, these elements are often referred to as non-metals.

Properties of Metals 

Physical Properties of Metals

Some physical properties of metals are listed below.

• Shiny (lustrous) in nature
• Metal is a good conductor of electricity and heat
• Density and melting point is high
• Mouldable (Malleable)
• Ductile
• At room temperature, it is in solid form except for mercury
• Opaque

Chemical Properties of Metals

Some chemical properties of metals are listed below.

• Easily corrodible
• Can lose electrons
• Form basic oxides
• Have low electronegativities
• Good reducing agents

Properties of Non-Metals

Physical Properties of Non-metals

Some physical properties of non-metals are listed below.

• Poor conductors of electricity and heat
• Non-Ductile metals
• Brittle solids
• Maybe solids, liquids or gases at room temperature
• These are not sonorous
• Transparent

Chemical Properties of Non-metals

Some chemical properties of non-metals are listed below.

• The number of electrons in the outer shell is generally 4-8
• Easily gain or lose valence electrons
• Form acidic oxides whenever they come in contact with oxygen
• High electronegative elements
• Great oxidizing agents

Non-metals and metals take different forms (allotropes). They have different shapes and properties. Allotropes are elements that exist in two or more than two different physical forms.

• Example 1: A non-metal carbon – two allotropes of carbon are diamond and graphite.
• Example 2: A metal such as iron – two allotropes of iron are austenite and ferrite

Have a look at the given table depicting the major differences between Metals And Non-metals for better understanding.

Differences Between Metals And Non-metals

A reactivity series is a vital tool for chemists. It helps us to understand the properties of metals and the differences between them.

3. Acids, Bases, and Salts

What are Acids, Bases, and Salts?

Many acids and bases occur naturally in nature, such as citric acid in fruits like orange, lemon etc, tartaric acid in tamarind, malic acid in apples and lactic acid in milk and milk products, hydrochloric acid in gastric juices.

Similarly, many bases are found such as lime water. We use many of these acids in our day-to-day life, such as vinegar or acetic acid in the kitchen, boric acid for laundry, baking soda for the purpose of cooking, washing soda for cleaning etc.

Many of the acids that we do not consume in the household are used in the laboratories and industries, which include an acid such as HCl, H₂SO₄ etc. and bases such as NaOH, KOH etc. When these acids and bases are mixed in the right proportions, the neutralization reaction thus results in the formation of salt and water. Some naturally occurring salts found in nature include NaCl and KCl etc in seawater and natural rock deposits. In this section, we will read more about acid, base and salt and their properties.

Definitions

1. Acid:- An acid is defined as a substance whose water solution tastes sour, turns blue litmus red and neutralizes bases.
2. Base:- A substance is called base if its aqueous solution tastes bitter, turns red litmus blue or neutralizes acids. 
3. Salt:- Salt is a neutral substance whose aqueous solution does not affect litmus.

Acids

The term acid is derived from a Latin word ‘acidus’ or ‘acere’, which means sour. The most common characteristic is their sour taste. An acid is a substance that renders ionizable hydronium ion (H₃O⁺) in its aqueous solution. It turns blue litmus paper red. These dissociate in their aqueous solution to form their constituent ions, as given by the following examples.

Based on their occurrence, they are divided into two types- Natural and mineral acids.

Natural Acids: These are obtained from natural sources, such as fruits and animal products. For e.g. lactic, citric, and tartaric acid etc.

Mineral Acids: Mineral acids are acids prepared from minerals. For example, Hydrochloric acid (HCl), Sulphuric Acid (H₂SO₄), and nitric acid (HNO₃) etc.

Also Check ⇒ Dilute Acids

Bases

The most common characteristic of bases is their bitter taste and soapy feel. A base is a substance that renders hydroxyl ion(OH^–) in their aqueous solution. Bases turn the colour of red litmus paper to blue.

Salts

Salt is an ionic compound that results from the neutralization reaction of acids and bases. Salts are constituted of positively charged ions, known as cations and negatively charged ions, known as anions, which can either be organic or inorganic in nature. These ions are present in a relative amount, thus rendering the nature of the salt neutral.

4. Carbon and its Compounds

What are Carbon Compounds?

Carbon is very reactive. It forms a huge number of compounds with many other elements. Compounds containing carbon outnumber the compounds of all the other elements.

Ethane which has two carbon atoms will need 6 hydrogen atoms to satisfy the valency of each carbon atom (keeping in mind the single bond existing between both the carbon atoms). Hence, the molecular formula for ethane is C₂H₆. Now, the bond between two or more carbon atoms involved in the formation of a compound can be single, double or even a triple bond.

Thus, on the basis of the number of bonds existing between the C-atoms involved in the formation of a compound we classify carbon compounds into two major categories: saturated and unsaturated carbon compounds.

Types of Carbon Compounds

1. Saturated Carbon Compounds

These are the compounds in which various carbon atoms in a chain or a ring are linked together by single bonds only. Alkanes are the most common examples of saturated chain carbon compounds. Ethane is a member of the alkane family whose structure is drawn below:

Structure of Ethane – Saturated Carbon Compound

2. Unsaturated Carbon Compounds

These are the compounds in which various carbon atoms in a chain or a ring are linked together by double or triple bonds. Alkenes (where carbon atoms are linked through double bonds) and alkynes (where carbon atoms are linked through triple bonds) are the most common examples of unsaturated chain carbon compounds. Ethene is a member of the alkene family whose structure is drawn below:

Structure of Ethene – Unsaturated Carbon Compound

Catenation Property of Carbon

• One of the most amazing properties of carbon is its ability to make long carbon chains and rings. This property of carbon is known as catenation.
• Carbon has many special abilities out of all one unique ability is that carbon forms pπ-pπ bonds which are nothing but double or triple bonds with itself and with other electronegative atoms like oxygen and nitrogen.
• Just because of these two properties of carbon i.e catenation and multiple bond formation, it has the number of allotropic forms.

The Existence of Carbon Compounds

Carbon is one of the more widespread heavy elements – it may make up almost 0.5 percent of the universe mass. The solar system formed from a material that was quite rich in carbon. Even then the element only makes up 0.025 percent of Earths crust and most of this carbon bound up in rocks and minerals such as limestone and chalk. But carbon is highly concentrated in living creatures and accounts for nearly one-quarter of atoms in our tissues.

The carbon compounds exist mainly in three ways:

1. Straight Chains

In such kind of arrangement one carbon atom is bonded to another carbon forming a straight line without developing any branches. Low molecular weight hydrocarbons exist in straight chains. For example ethane

2. Branches

Carbon compounds with higher molecular weight mostly exist in branched form i.e. one of the carbon atoms is bonded to more than two carbon atoms. For example isopentane.

Structure of Isopentane

3. Rings

In this kind of arrangement, three or more carbon atoms are linked together in such a way that they form closed cycles. Such compounds are also known as cyclic compounds. For example, cyclohexane.

Structure of Cyclohexane – Carbon Compounds

Solved Example

Question:

Why is it necessary to involve sp² hybridization to explain bonding in C₂H₄?

Solution:

C₂H₄ contains a carbon-carbon double bond in which a carbon atom is bonded to only three other atoms and hence sp² hybridization takes place.