Chemistry Chapter – 1: Matter, Atoms And Molecules
12 August, 2024
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
Taking into consideration different factors, chemical reactions are grouped into multiple categories. Few examples are: Combination | Decomposition Single | Displacement | Double displacement | Redox | Endothermic | Exothermic
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
Taking into consideration different factors, chemical reactions are grouped into multiple categories. Few examples are: Combination | Decomposition Single | Displacement | Double displacement | Redox | Endothermic | Exothermic
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
Itis 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
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:
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.
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
Write the answer of the following questions.
Which of the following correctly represents 360g of water? (i) 2 moles of water (ii) 20 moles of water (iii) 6.022 × 1023 molecules of water (iv) 1.2044 × 1025 molecules of water
(a) (i) (b) (i) and (iv) (c) (ii) and (iii) (d) (ii) and (iv)
Which of the following statements is not true about an atom? (a) Atoms are not able to exist independently. (b) Atoms are the basic units from which molecules and ions are formed. (c) Atoms are always neutral in nature. (d) Atoms aggregate in large numbers to form the matter that we can see, feel or touch.
1 u or 1 amu means (a) 1/12th mass of C-12 atoms (b) Mass of C-12 atom (c) Mass of O-16 atom (d) Mass of Hydrogen molecule
Which of the following contains maximum number of molecules? (a) 19 CO2 (b) 1 g N2 (c) 1 g H2 (d) 1 g CH4
A sample of NH3 molecule irrespective of source contains 82.35% Nitrogen and 17.65% of Hydrogen by mass. This data supports: (a) Law of Conservation of Mass (b) Las of Multiple Proportions (c) Law of Definite Proportions (d) Avogadro’s Law
An element X is divalent and another element Y is tetravalent. The compound formed by these two elements will be: (a) XY (b) XY2 (c) X2Y (d) XY4
The molecular formula of potassium nitrate is ________. (a) KNO3 (b) KNO (c) KNO2 (d) KON
3.42 g of sucrose are dissolved in 18 g of water in a beaker. The numbers of oxygen atoms in the solution are: (a) 6.68 ×1023 (b) 6.09 ×1022 (c) 6.022 ×1023 (d) 6.022 ×1021
Molecular mass is defined as the: (a) Mass of one molecule of any substance compared with the mass of one atom of C – 12 (b) Mass of one atom compared with the mass of one atom of hydrogen (c) Mass of one atom compared with the mass of one molecule (d) None of the above
A change in the physical state can be brought about (a) only when energy is given to the system (b) only when energy is taken out from the system (c) When energy is either given to, or taken out from the system (d) Without any energy change
The atomic mass of sodium is 23. The number of moles in 46g of sodium is ________. (a) 4 (b) 2 (c) 0 (d) ½
Which of the following represents a correct chemical formula? (a) CaCl (b) BiPO (c) NaSO4 (d) NaS
What is the formula mass unit of ZnO? (a) 18 u (b) 81 u (c) 88 u (d) 188 u
How many atoms of oxygen are present in 300 grams of CaCO3? (a) 54.207 × 1023 (b) 6.207 × 1023 (c) 12.207 × 1023 (d) 22.2 × 1023
Which of the following represents the correct relation between Avogadro’s number (No), number of particles (N) and moles (n)? (a) n = N / No (b) n = No / N (c) n = N No (d) all are correct
A neutron carries a positive charge. A. True B. False
How many atoms of nitrogen are in the formula NH4OH? A.4 B.3 C.2 D.1
How many atoms of oxygen are in Sn(SO4)2? A.2 B.4 C.6 D.8
Identify the atomic number of the element of Xenon. A.50 B.52 C.53 D.54
Which of the following determines the atomic number of an atom? A. Number of neutrons B. Number of electrons C. Number of protons D. Number of isotopes
A proton has a charge that is equal in force but opposite in charge of each electron. A. True B. False
Protons and electrons are about equal in mass. A. True B. False
The mass of an atom depends on the number of protons and neutrons in its nucleus. A. True B. False
How do you determine the mass number of an atom? A. It is equal to the number of protons. B. It is equal to the number of protons plus the number of electrons. C. It is equal to the number of protons plus the number of neutrons. D. It is equal to the number of electrons plus the number of neutrons. E. It is equal to the number of protons minus the number of neutrons.
Atoms of the same element with different numbers of neutrons are called__________. A. Isotopes B. Ions C. Atoms D. Either isotopes or ions E. None of these are correct
In the name carbon-14, the 14 is the _________________. A. Mass number B. Atomic number C. Oxidation number D. Number of electrons E. Number of neutrons
What is the atomic number of the element Xenon? A. 50 B. 54 C. 60 D. 82
The atomic number of an atom is determined by the number of A. Neutrons B. Electrons C. Protons D. Isotopes
An atom that has a different number of electrons and protons is called a(n) A. Ion B. Isotope C. Molecule D. Element
Neutrons have a ____________ charge. A. Positive B. Negative C. Neutral D. No charge
How many protons are in tin-100? A. 40 B. 50 C. 60 D. 100
How many neutrons are in tin-100? A. 40 B. 50 C. 60 D. 100
Is tin-100 a common isotope? A. Yes B. No C. Sometimes D. Rarely
What is the charge on an atom with 10 protons and 8 electrons? A. 2 B. -2 C. 0 D. 1
Which of the following describes the process in which an atom gains or loses electrons? A. Ionization B. Electron Affinity C. Nuclear Fusion D. Atomic Fusion