Chemistry Chapter - 1: Matter, Atoms And Molecules

Introduction : Matter, Atoms And Molecules

Matter

Air, water, stones, sand, clouds, pencils, books – Everything is made up of matter. Matter is everything in this universe that occupies space and has mass.

Characteristics of matter:

Matter is made up of small particles called atoms.
These particles are too small to be observed with naked eye.
These particles are constantly moving constantly.
These particles have spaces between them.
Particles of matter attract each other because of the force of attraction.

States of matter:

Matter can be classified as solid, liquid and gas on the basis of interparticle forces and the arrangement of particles.
These three forms of matter are interconvertible by increasing or decreasing pressure and temperature. For example, ice can be converted from solid to a liquid by increasing the temperature.

Diffusion

The zig zag or random path travelled by the matter is called the Brownian motion.
When the particles of matter intermix on their own with each other, the phenomenon is called diffusion. For example, spreading of ink in water. During diffusion, the particles occupy the interparticle spaces.

The rate of diffusion increases with increase in the temperature, due to increase in kinetic energy of the particles.

Difference between the characteristic states of matter

Effect of change of temperature on states of matter

The kinetic energy of matter particles increases as temperature rises, and they begin to vibrate at a higher frequency. As a result, the interparticle force of attraction between particles decreases, and particles become separated from their positions and free to travel.
The state of matter begins to change as a result.
Liquids are formed when solids undergo a phase transition.
Liquids, too, go through a phase change to become gases.

Melting point-
The melting point of a solid is defined as the temperature at which solid melts to become liquid at the atmospheric pressure. At melting point, these two phases, i.e., solid and liquid are in equilibrium, i.e., at this point both solid state and liquid state exist simultaneously.

Boiling point –
The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.

Latent heat of fusion –
It is the amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.

Latent heat of vaporization –
It is the amount of heat energy that is required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point.

Sublimation –
The transition of a substance directly from its solid phase to gaseous phase without changing into the liquid phase (or vice versa) is called sublimation.

Effect of change in pressure on state of matter –
By applying pressure, the interparticle spaces between particles of matter decreases. Thus, by applying pressure and reducing temperature we can convert a solid to liquid and a liquid to gas.

Elements are further grouped into the following three categories:

Metals, for example: Iron, copper, gold, sodium, silver, mercury, etc.
Non – metals, for example: Carbon, oxygen, sulphur, nitrogen, oxygen, hydrogen, etc.
Metalloids: Boron, silicon, germanium, etc.

Properties of Non-metals:

These are dull in appearance.
They are poor conductors of heat and electricity except diamond which is a good conductor of heat and graphite which is a good conductor of electricity.
They are neither malleable nor ductile.
They are generally soft except diamond which is the hardest natural substance known.
They may be solids, liquids or gases at room temperature.

Metalloids:

The elements that have properties intermediate between those of metals and non-metals, are called metalloids.

Difference between types of mixtures

Ways of representing the concentration of a solution

Mass by the mass percentage of a solution = (Mass of solute / Mass of solution) × 100
Mass by volume percentage of a solution = (Mass of solute/ volume of solution)×100

Tyndall effect:
it is the scattering of light by particles in a colloid or else particles in a very fine suspension. e.g. It can be observed when sunlight passes through the canopy of a dense forest.

Centrifugation :
it uses centrifugal force for the separation of two liquids in a mixture. Here, a denser component of the mixture migrates away from the axis, and lighter component migrates towards the axis.

Chromatography :
it is used to separate the different components in a liquid mixture. It is based on the different properties of compounds in two phases: stationary and mobile phase.

Distillation :
It is a method for separating the component substances from a liquid mixture by selective evaporation and condensation. Used in: Production of gasoline, distilled water, xylene, alcohol, paraffin, kerosene etc.

Fractional Distillation :
it is the separation of a mixture into its component parts or fractions by their melting points. This is the process of separation of chemical compounds by their boiling point. The mixture is heated to a temperature at which one or more fractions will vaporize.

Crystallization :
It is a separation technique in which solids are separated from a solution. In this technique, the solvent molecules start evaporating, leaving behind the solutes when the solution is heated in an open container.

Physical Property of a Substance:
Properties of a substance such as rigidity, colour, fluidity, boiling point, melting point, density and hardness which we can observe are called as Physical Properties.

Physical Change:
When physical properties of a substance change it is known as a Physical Change. When we convert a substance from one state to another, such as a solid into a liquid or vice-versa, it is also a physical change as only the physical nature of the substance changes without affecting its chemical nature.

For Example, Change of ice into water. The chemical properties of water remain the same.

Chemical Property of a Substance:
The chemical nature of a substance is known as its Chemical Property such as its odour or its chemical composition.

Chemical Change:
When the chemical properties or chemical composition of a substance gets altered it is called a chemical change. It is also called as a Chemical Reaction.

For Example, Burning of paper.

Mixture v/s compound

Chemical reaction

Two or more molecules interact to produce new compounds and are called reactants, whereas the newly formed compounds are called products. In a chemical reaction, a chemical change must occur, which is generally observed with physical changes like precipitation, heat production, colour change, etc.

Laws of chemical combination

Law of conservation of mass – mass can neither be created nor destroyed in a chemical reaction
Law of constant proportion/Law of definite proportion – the elements are always present in definite proportions by mass in a chemical substance. For example, Hydrogen and oxygen are present in water in a ratio of 1:8. So if we decompose 9g of water we will obtain 1g of hydrogen and 8g of oxygen.

Atom

An atom is the defining structure of an element, which cannot be broken by any chemical means. The atomic symbol has three parts
The symbol X: the usual element symbol
The atomic number A: equal to the number of protons
The mass number Z: equal to the total number of protons and neutrons in an element.

Dalton’s atomic theory

The matter is made up of tiny particles called atoms that cannot be divided.
Atoms are never formed or destroyed during a chemical reaction.
Atoms are never formed or destroyed during a chemical reaction.

Atomic mass

it is the total of the masses of the electrons, neutrons, and protons in an atom, or in a group of atoms. It can be best defined as 1/12 of the mass of a carbon-12 atom in its ground state.

Molecular mass

Molecular mass of an element is defined as the sum of the masses of the elements present in the molecule. It is obtained by multiplying the atomic mass of an element with the number of atoms in the molecule and then adding the masses of all the elements in the molecule.

Mole concept & Avogadro Number:

In a substance, the amount of entities present for e.g. atoms, molecules, ions, is defined as a mole. A mole of any substance is 6.022×10²³ molecules. Mole concept is one of the most convenient ways of expressing the amount of reactants and product in the reaction.
The value of Avogadro’s number is approximately 6.022×10²³. The definition of Avogadro’s number is that it tells us the number of particles in 1 mole (or mol) of a substance. These particles could be electrons or molecules or atoms.

Molar mass-
A substance is something which has mass and occupies space. The molar mass/molecular weight is actually the sum of the total mass in grams of the atoms present to make up a molecule per mole.

The unit of molar mass is grams/mole.

Molecules of Elements-
The molecules of an element are formed by combinations of similar types of atoms.

For example, Helium (He) is made up of only one atom while oxygen is made up of two atoms.

Atomicity –
the number of atoms in a molecule of an element is called its atomicity.

For example, helium is monoatomic and oxygen is diatomic:

Monoatomic – when an element comprises of a single atom. Example – all metals

Diatomic – when an element comprises of two atoms. Example – all gases

Triatomic – when an element comprises of three atoms

Tetra-atomic – when an element comprises of four atoms

Poly-atomic – when an element comprises of more than two atoms

Ions

Compounds contain metals as well as non-metals. These elements include charged species which are known as ions. Thus, ion is a particle that has a positive or negative charge.

Anion – negatively charged ion
Cation – positively charged ion
There can be a single charged atom in an ion or there may be a group of charged atoms in an ion that have a net charge on the compound. When a group of atoms carries a charge in a compound it is called as a polyatomic ion.

Cation – positively charged ion

There can be a single charged atom in an ion or there may be a group of charged atoms in an ion that have a net charge on the compound. When a group of atoms carries a charge in a compound it is called as a polyatomic ion.

Valency-
Valence electrons are those electrons which are present in the outermost orbit of the atom.

The capacity of an atom to lose, gain or share valence electrons in order to complete its octet determines the valency of the atom.

Chemical formula-
We use a chemical formula to represent the composition of a compound in the form of symbols.

To write a chemical formula you must know two things –

1. Symbols of elements

2. Valency

Rules of writing a Chemical Formula

Valencies of on the ions must balance.
In a case where both metal and non-metal substances are present in a compound, the name of the metal is always written first in the chemical formula. For example, Sodium Chloride is written as NaCl
In case of polyatomic ions, the ion is written in brackets before writing the number of ions associated to it. In case of a single ion, there is no need to mention the ion in brackets

How to write a Formula of a Compound

Write the symbols of the corresponding elements of the compound as explained above
Write the valencies of the elements of the compound
Crossover the valencies of the elements.

Thomson’s Model of an Atom

According to J.J. Thomson, the structure of an atom can be compared to Christmas pudding where electrons are present inside a positive sphere.

An atom is composed of a positively charged sphere in which electrons are embedded.

Atom is neutral as the positive and negative charged are equal in proportion.

Neil bhor’s model of atom

Electrons revolve around the nucleus in stable orbits without emission of radiant energy. Each orbit has a definite energy and is called an energy shell or energy level.
An orbit or energy level is designated as K, L, M, N shells. When the electron is in the lowest energy level, it is said to be in the ground state.
An electron emits or absorbs energy when it jumps from one orbit or energy level to another.
When it jumps from a higher energy level to lower energy level, it emits energy while it absorbs energy when it jumps from lower energy level to higher energy level.

Isotopes and Isobars-

Isotopes are defined as the atoms of the same element, having the same atomic number ( number of protons ) but different mass numbers ( number of protons+neutrons ).

Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars. For example, Calcium and Argon: both have the same mass number – 40 . ₂₀Ca⁴⁰ and ₁₈Ar⁴⁰

Chemical reaction

Chemical reactions are chemical changes in which reactants transform into products by making or breaking of bonds (or both) between different atoms.

Types of chemical reactions

Chemical reaction

Chemical reactions are chemical changes in which reactants transform into products by making or breaking of bonds (or both) between different atoms.

Types of chemical reactions

Steps to form Balanced Equation

To show how to balance the equation, the following equation is used-
Fe + H₂O → Fe₃O₄ + H₂

Step 1: First of all, draw the boxes around each formula as shown below-
Step 2: Find out the number of atoms of each element. For Example, on reactant side, 1 for Fe, 2 H, and 1 O and on product side we have, 3 for Fe, 4 for O and 2 for H.
Step 3: Start to balance the equation with the compound having maximum number of atoms. While balancing does not alter the formula of the compound.
Step 4: One by one balance each element on reactant and product side.

Step 5: After balancing number of atoms on both the side of the equation, finally check the correctness of the balanced equation.

Step 6: then write the symbols of the physical state of reactants and products as shown below-
3Fe(s) + 4H₂O (g) → Fe₃O₄ (s) + 4H₂ (g)
This above equation represents the balanced equation.

Combination reaction
In a combination reaction, two elements or one element and one compound or two compounds combine to give one single product.

Decomposition Reaction

It is type of reaction which involves breakdown of single reactant into simpler products. Decomposition of silver chloride into silver and chlorine in presence of sunlight is an example of decomposition reaction.

Displacement Reaction

It is a reaction in which more reactive element will displaces the less reactive element. Example of Displacement Reaction:

Redox Reaction

It is also known as Oxidation-reduction Reaction. In this type of reaction transfer of electrons occurs between the two species.

Oxidation is defined as addition of oxygen or removal of hydrogen. Reduction is defined as removal of oxygen or addition of hydrogen.

Oxidizing agent is the one which gains the electrons and is reduced in a chemical reaction. Reducing agent is oxidized in a chemical reaction and it loses the electrons.

Fluorine is the strongest oxidizing agent. Formic acid is a reducing agent. Example of Redox Reaction:

Redox Reaction

Endothermic and exothermic reaction

Exothermic reaction

heat is evolved during a reaction. Most of the combination reactions are exothermic.

Al + Fe₂O₃→ Al₂O₃+ Fe + heat
CH₄+ 2O₂→ CO₂+ 2H₂O + heat

Endothermic

Heat is required to carry out the reaction.
6CO₂+ 6H₂O + Sunlight → C₆H₁₂O₆+ 6O₂
Glucose
Most of the decomposition reactions are endothermic.

Corrosion

Gradual deterioration of a material, usually a metal, by the action of moisture, air or chemicals in the surrounding environment.

4Fe(s) + 3O₂(from air) + xH₂O(moisture) → 2Fe₂O₃.xH₂O(rust)
Corrosion of copper:
Cu(s) + H₂O(moisture) + CO₂(from air) → CuCO₃.Cu(OH)₂(green)
Corrosion of silver:
Ag(s) + H₂S (from air) → Ag₂S(black) + H₂(g)

Rancidity

It refers to the oxidation of fats and oils in food that is kept for a long time. It gives foul smell and bad taste to food. Rancid food causes stomach infection on consumption.

Prevention:
1. Use of air-tight containers
2. Packaging with nitrogen
3. Refrigeration
4. Addition of antioxidants or preservatives