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Chapter 3 – Atoms and Molecules

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:


What is an atom?

Atom is the smallest component in which matter may be separated without the release of electrically charged particles. It is also the smallest unit of matter with the characteristic properties of a chemical substance. The atom is the fundamental building block for chemistry. Atoms are hollow spaces. This space consists of a positively charged nucleus of protons and neutrons covered by a cloud of negatively charged electrons.

Atoms are made up of three basic particle types: 

  • Protons
  • Electrons 
  • Neutrons 

Neutrons and protons have approximately the same mass, and the mass of an electron is negligible in comparison to that. A proton carries a positive charge, there is no charge for a neutron and an electron is charged negatively. An atom contains an equal number of protons and electrons, so an atom has no charge overall. An atom’s nucleus contains only protons and neutrons and is therefore positively charged. The electrons occupy the spatial region around the nucleus. Most of the mass is, therefore, concentrated within the nucleus. 

The size of an atom is extremely small, enough smaller than what we imagine. When more than a million atoms are accumulated together, a film of an atom as thick as a slim sheet of paper is created. The size of a detached atom is difficult to measure because the locations of electrons enclosing the nucleus are hard to locate. Avogadro’s Law helps in defining atomic size.

However, by considering that the distance between adjacent atoms is equivalent to half the radius of an atom, the size of an atom can be determined. In general, the atomic radius is estimated in nanometers. 

1 m = 10^9nm 

In a chemical element, atomic weight is the mass of an atom. It is roughly equivalent to the total atomic neutrons and protons. It is expressed in units of atomic mass (denoted by u). The molar mass of 1 atom of C-12 is equal to exactly one-twelfth and the relative atomic masses of elements are determined with respect to-12 atoms. 

A molecule is defined as the smallest unit of a compound containing the compound’s chemical properties. Molecules are composed of atomic groups.

Mole Concept

The mole concept is a formula which helps us calculate the number of atoms or molecules. The formula is: 

Number of Atoms or Molecules = (Number of Moles)*(6.022*1023)

The Forces between Atoms and Molecules

The simplest forces between atoms are those that occur as a consequence of the movement of electrons. A basic example is that of sodium fluoride. The sodium atom has a nuclear load of +11, with 2 electrons in the K shell, 8 in the L shell and 1 in the M shell. The nuclear charge of the fluorine atom is 9 with 2 electrons in the K shell and 7 in the L shell.

The outermost electron of the sodium atom can be quickly moved to the fluorine atom; all atoms then have a full shell, but sodium has a net charge of +1 and fluorine a net charge of-1. As a consequence, these ions attract each other by direct coulombic contact. The force between them is high and differs as x-2, where x is the distance between the ions, and it works in the direction of the line connecting the ions.

Moreover, it is unsaturated – one positive ion will draw multiple negative ions around it, and the force exerted by the positive ion on each negative ion is not influenced by the influence of other negative ions. Of addition, negative ions will repel each other as well.

  • Any substance is made up of atoms that are minute particles. 
  • Atoms are indivisible particles that, by chemical reactions, can not be destroyed or formed. Laws of chemical combination assist this theory.
  • The atoms of an element have the same chemical and mass properties, while atoms of different elements have different chemical and mass properties. 
  • In a ratio of small integral quantities, atoms join to form compounds.

Laws of chemical combination constitutes of:

Law of Conservation of Mass

In basic words, this law specifies that the matter cannot be created or destroyed. In other terms, the overall mass, that is, the sum of the reaction mixture mass and the products produced, stays unchanged. Antoine Lavoisier adopted this law in 1789 on the basis of the evidence he collected following close analysis of various combustion reactions.

Gay Lussac’s Law of Gaseous Volumes

Gay Lussac gave this law in 1808 on the basis of his findings. This law provides that when gases are generated or mixed in a chemical reaction, they do so in a simple volume ratio, provided that all gases are at the same temperature and pressure. This law can be viewed as another type of law of definite proportions. The main distinction between these two rules of chemical mixture is that the rule of Gay Lussac is laid out in terms of volume, whereas the law of some proportions is set out in terms of mass.

Avogadro’s Law Molar Mass

This law was proposed by Avogadro in 1811. It claimed that under the same conditions of temperature and pressure, the equal amount of all gases comprises an equal number of molecules. This ensures that 2 litres of hydrogen would contain the same amount of molecules as 2 litres of oxygen, since all gases are at the same temperature and pressure.

Law of Multiple Proportions

It states that as two components join to create more than one compound, the weights of one element, which combine with the defined weight of the other, are in the ratio of small whole numbers.

1. Define the atomic mass unit.

The atomic unit of mass is exactly described as 1/12 the mass of the carbon-12 atom. The carbon-12 atom holds six neutrons and six protons in its nucleus. The mass of the atomic unit is symbolized as AMU or AMU.

1 AMU = Average rest mass of the proton and rest mass of the neutron.

1 AMU = 1.67377 x 10-27 kilogrammes or 1.67377 x 10-24 grammes.

This chapter taught us the basics of atoms and molecules. We learned important concepts like atomic mass and size which will help in understanding Gay Lussac’s law of gaseous volumes and law of multiple proportions.

1. What is the difference between atoms and molecules? 

Atoms are regarded as the ‘primary building blocks of matter.’ The smallest constituent unit of the substance is the characteristics of the chemical element. One or more atoms connected by covalent (chemical) bonds are made up of molecules. 

2. What are the 4 types of atoms? 

  1. Isotopes
  2. Radioactive
  3. Unstable Ions 
  4. Antimatter

3. How many atoms are in a molecule? 

Two atoms 

Molecule: a group of two or more atoms that are held together by chemical bonds. Therefore, to form a molecule, at least 2 atoms are required.

4. What is bigger: atom or molecule? 

Atoms are smaller than molecules and are the smallest building blocks of matter as well. When two or more atoms bond, they form molecules.

5. Can an atom be created? 

It is impossible to create or destroy atoms, and they are indestructible; it is possible to break them into smaller parts. This was based on the law of conservation of mass.

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High School Physics

  • Alternating Current
  • Atoms
  • Communication Systems
  • Current Electricity
  • Dual nature of Radiation and Matter
  • Electric Charges and Fields
  • Electricity
  • Electromagnetic Induction
  • Electromagnetic Waves
  • Electron Beams and Radioactivity
  • Electrons and Photons
  • Electrostatic Potential and Capacitance
  • Fluid Pressure
  • Force and Acceleration
  • Force And Laws Of Motion
  • Gravitation
  • Internal Energy
  • Kinetic Theory
  • Law of motion
  • Light – Reflection And Refraction
  • Magnetic Effects Of Electric Current
  • Magnetism and Matter
  • Management Of Natural Resources
  • Mechanical properties of Fluids
  • Mechanical properties of Solids
  • Motion
  • Motion in a plane
  • Motion in a straight line
  • Moving Charges and Magnetism
  • Nuclear Energy
  • Nuclei
  • Oscillations
  • Our Environment
  • Paths of Heat
  • Physical world
  • Ray optics and optical instruments
  • Semiconductor Devices
  • Semiconductor Electronics: Materials, Devices and Simple Circuits
  • Simple Machines
  • Sound
  • Sources Of Energy
  • Specific and Latent Heats
  • Spherical Mirrors
  • Static Electricity
  • Systems of Particles and Rotational motion
  • Thermal properties of matter
  • Thermodynamics
  • Units and Measurement
  • Vectors, Scalar Quantities and Elementary Calculus
  • Wave Optics
  • Waves
  • Work, Power and Energy

High School Chemistry

  • Acids, Bases and Salts
  • Alcohols, Phenols and Ethers
  • Aldehydes, Ketones and Carboxylic Acids
  • Aliphatic and Aromatic Hydrocarbons
  • Alkyl and Aryl Halides
  • Amines
  • Analytical Chemistry 
  • Atomic Structure
  • Atoms And Molecules
  • Basic concepts of Chemistry
  • Biomolecules
  • Carbon And Its Compounds
  • Carboxylic acids and Acid Derivatives
  • Chemical Bonding and Molecular Structures
  • Chemical Energetics
  • Chemical Equilibria
  • Chemical Kinetics
  • Chemical Reactions And Equations
  • Chemical Reactions and Their Mechanisms
  • Chemistry in Everyday Life
  • Chemistry of p-Block elements
  • Chemistry of Transition and Inner Transition
  • Classification of Elements
  • Coordination Compounds
  • Cyanide, Isocyanide, Nitro compounds and Amines
  • Electrochemistry
  • Electrolysis
  • Elements, Compounds and Mixtures
  • Environmental Chemistry
  • Equilibrium
  • Ethers and Carbonyl compounds
  • Haloalkanes and Haloarenes
  • Hydrocarbons
  • Hydrogen
  • Ideal solutions
  • Introduction to Organic Chemistry
  • Ionic equilibria
  • Matter
  • Matter Around Us
  • Matter In Our Surroundings
  • Metallurgy
  • Metals And Non-Metals
  • Mole Concept and Stoichiometry
  • Natural Resources
  • Organic Chemistry – Basic Principles
  • Periodic Classification of Elements
  • Physical and Chemical Changes
  • Physical and Chemical Properties of Water
  • Polymers
  • Preparation, Properties and Uses of Compounds
  • Principles and Processes of Isolation of Elements
  • Redox Reactions
  • Relative Molecular Mass and Mole
  • States of Matter
  • Structure Of The Atom
  • Study of Compounds
  • Study of Gas Laws
  • Study of Representative Elements
  • Surface Chemistry
  • The d-block and f-block elements
  • The Gaseous State
  • The p-Block Elements
  • The Periodic Table
  • The s-Block Elements
  • The Solid State
  • Thermodynamics

High School Biology

  • Absorption and Movement of Water in Plants
  • Adolescent Issues
  • Anatomy of Flowering Plants
  • Animal Kingdom
  • Bacteria and Fungi-Friends and Foe
  • Biodiversity and Conservation
  • Biofertilizers
  • Biological Classification
  • Biomedical Engineering
  • Biomolecules
  • Biotechnology and its Applications
  • Biotic Community
  • Body Fluids and Circulation
  • Breathing and Exchange of Gases
  • Cell – Unit of Life
  • Cell Cycle and Cell Division
  • Cell Division and Structure of Chromosomes
  • Cell Reproduction
  • Cellular Respiration
  • Chemical Coordination and Integration
  • Circulation
  • Control And Coordination
  • Crop Improvement
  • Digestion and Absorption
  • Diversity In Living Organisms
  • Ecosystem
  • Environmental Issues
  • Excretory Products and their Elimination
  • Flowering Plants
  • Genes and Chromosomes
  • Health and Diseases
  • Health and Its Significance
  • Heredity And Evolution
  • Heredity and Variation
  • How Do Organisms Reproduce?
  • Human Diseases
  • Human Eye And Colourful World
  • Human Health and Disease
  • Human Population
  • Human Reproduction
  • Hygiene
  • Improvement In Food Resources
  • Integumentary System- Skin
  • Kingdom Fungi
  • Kingdom Monera
  • Kingdom Protista
  • Life Processes
  • Locomotion and Movement
  • Microbes in Human Welfare
  • Mineral Nutrition
  • Molecular Basis of Inheritance
  • Morphology of Flowering Plants
  • Neural Control And Coordination
  • Nutrition in Human Beings
  • Organism and Population
  • Photosynthesis
  • Photosynthesis in Higher Plants
  • Plant Growth and Development
  • Plant Kingdom
  • Pollination and Fertilization
  • Pollution; Sources and its effects
  • Principles of Inheritance and Variation
  • Reproduction and Development in Angiosperms
  • Reproduction in Organisms
  • Reproductive Health
  • Respiration in Human Beings
  • Respiration in Plants
  • Respiratory System
  • Sexual Reproduction in Flowering Plants
  • Strategies for Enhancement in Food Production
  • Structural Organisation in Animals
  • Structural Organisation of the Cell
  • The Endocrine System
  • The Fundamental Unit Of Life
  • The Living World
  • The Nervous System and Sense Organs
  • Tissues
  • Transpiration
  • Transport in Plants

High School Math

  • Algebra – Arithmatic Progressions
  • Algebra – Complex Numbers and Quadratic Equations
  • Algebra – Linear Inequalities
  • Algebra – Pair of Linear Equations in Two Variables
  • Algebra – Polynomials
  • Algebra – Principle of Mathematical Induction
  • Algebra – Quadratic Equations
  • Binomial Theorem
  • Calculus – Applications of Derivatives
  • Calculus – Applications of the Integrals
  • Calculus – Continuity and Differentiability
  • Calculus – Differential Equations
  • Calculus – Integrals
  • Geometry – Area
  • Geometry – Circles
  • Geometry – Conic Sections
  • Geometry – Constructions
  • Geometry – Introduction to Euclid’s Geometry
  • Geometry – Three-dimensional Geometry
  • Geometry – Lines and Angles
  • Geometry – Quadrilaterals
  • Geometry – Straight Lines
  • Geometry – Triangles
  • Linear Programming
  • Matrices and Determinants
  • Mensuration – Areas
  • Mensuration – Surface Areas and Volumes
  • Number Systems
  • Number Systems – Real Numbers
  • Permutations and Combinations
  • Probability
  • Sequence and Series
  • Sets and Functions
  • Statistics 
  • Trignometry – Height and Distance
  • Trignometry – Identities
  • Trignometry – Introduction

Middle School Science

  • Acids, Bases And Salts
  • Air and Its Constituents
  • Basic Biology
  • Body Movements
  • Carbon and Its Compounds
  • Cell – Structure And Functions
  • Changes Around Us
  • Chemical Effects Of Electric Current
  • Chemistry in Your Life
  • Coal And Petroleum
  • Combustion And Flame
  • Components Of Food
  • Conservation Of Plants And Animals
  • Crop Production And Management
  • Electric Current And Its Effects
  • Electricity And Circuits
  • Elements and Compounds
  • Fibre To Fabric
  • Food production and management
  • Force And Pressure
  • Forests: Our Lifeline
  • Friction
  • Fun With Magnets
  • Garbage In, Garbage Out
  • Getting To Know Plants
  • Health and Hygiene
  • Heat
  • Hydrogen
  • Life Processes: Nutrition in Animals and Plants
  • Light, Shadows And Reflections
  • Materials: Metals And Non-Metals
  • Matter and Its States
  • Metals and Non-metals
  • Micro Organisms: Friend And Foe
  • Motion And Measurement Of Distances
  • Motion And Time
  • Nutrition In Animals
  • Nutrition In Plants
  • Organization in Living Things
  • Our Environment
  • Physical And Chemical Changes
  • Pollution and conservation
  • Pollution Of Air And Water
  • Reaching The Age Of Adolescence
  • Reproduction In Animals
  • Reproduction In Plants
  • Respiration In Organisms
  • Rocks and Minerals
  • Separation Of Substances
  • Simple Machines
  • Soil
  • Some Natural Phenomena
  • Sorting Materials Into Groups
  • Sound
  • Stars And The Solar System
  • Structure of Atom
  • Synthetic Fibers And Plastics
  • The Living Organisms And Their Surroundings
  • Transfer of Heat
  • Transformation of Substances
  • Transportation In Animals And Plants
  • Universe
  • Waste-water Story
  • Water: A Precious Resource
  • Weather, Climate And Adaptations Of Animals To Climate
  • Winds, Storms And Cyclones

Middle School Math

  • Addition
  • Area and Its Boundary
  • Boxes and Sketches
  • Data Handling
  • Fun With Numbers
  • Heavy and Light
  • How Many
  • Long And Short
  • Mapping
  • Measurement
  • Money
  • Multiplication and Factors
  • Multiply and Divide
  • Numbers
  • Parts and Wholes
  • Pattern Recognition
  • Patterns
  • Play With Patterns
  • Rupees And Paise
  • Shapes And Angles
  • Shapes And Designs
  • Shapes and Space
  • Similarity
  • Smart Charts
  • Squares
  • Subtraction
  • Tables And Shares
  • Tenths and Hundredths
  • Time
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