CTF Gat saa Seas For Class 7Goyal’s uT FOUNDATION COURSE HEMISTRY Class 7 By Achanta Ramakrishna Principal Johnson Foundation School Principal, ISC Plus Care Johnson Grammar School ICSE Senior School Campus, Hyderabad SPECIMEN Co FOR SALE GOYAL BROTHERS PRAKASHANBROTHERS PRAKASHAN TIONAL PUBLISHERS EDUCA Sales & Registered Office + < oass 11/1903, Chuna Mandi, Paharganj, New Detht 10, Phones | 43SS1877, 43561877 Post Box Eainail » infixiegoyal-books com Website = weve goyal-books com Administrative Office : or 63, Noida-2OL301 (UP) Phone | 0120-4085: SHOWROOMS £ YA10, Dev Castle Complex Opp. Radhekrishan Villa, Jaymala- Govindwadi Road Isanpur, Ahmedabad-382 443 (Gujarat) Tel : 09925004030 Chennai: No. 50/39, Ground Floor, Five Furioing Road. Guindy Chennai-600 032 (Tamil Nadu) Phones : 044-22552778, 044-22552767 Guwahati: Plot No. 1179, KRE Road, Bharalumuth, near Post Office, Fasway Gate No. 8, Guwahati-781009 (Assam), Phone : 0361-2735337 ‘Agarwal Chambers, 5-9-1121, King Kothi Road, D2. Hyderabad: F-7/8/41, First Floor, Hyderabad - 500001, Tele-fax : 23211332 Kochi + Fair Heavens, H.No. 52-278/A, Shine Road. Vyttila Emakulam - 682019 (Kerala) Phone : 0484-230528 lagdish Chandra No. 203, 2nd Floor, Fomra Towers, S4-A, Acharya J Bose Road, Kolkata - 700014, Phone : 033-22262683 Bengaluru: 1681/5/4, Ground Floor, 3rd Main Ramamohanapuram, Bengaluru - 560 021, Phone : 080-23320855 Plot No. 203, Zone-Il, M.P. Nagar, Bhopal-#62 011 (MP), Kolkata Bhopal : Tele-fax : 0755-4271371 Lucknow: B-319, Sector-B, Mahanagar, Opposite PAC Main Gate, Lucknow - 226 006, Phone : 0522-2320841 Patna + Ravi Kiran Apartment, Flat No. 2-A, Second floor, Near Water Pumping Station, Pani Tanki Lane, Pirmohani, Patna ~ 500003 Nagpur + Thakkar Villa House No. 436 Joshiwadi, Sitabuldi, 9823655077 Nagpur - 440012, Phon To Fay our Books oaline Ing on to wewagoyal boakecom © Reserved Edition : 2023 7205 Disclaimer Due care and diligence has been taken while writing, editing and printing the Dock Neither the author nor the publishers of the book hold any responsibilty for any mustakes that may have inadvertently crept in Published & Printed by Roshan Lal Goyal for Goyal Brothers Prakashan, New DelhiPreface iti s in order In today’s competitive world, students need to tackle ee es to ensure a successful career. This can be achieved only ted wing cation ee knowledge of the subject which will help them to strengt! es tne the fundamental concepts and enhance their problem solving skills. The “IIT Foundation Series — Chemistry” books for Classes 6 ie Sesion to provide a solid base to the students who aspire to undertake tl 2 a oe competitive exams for entrance to enginecring institutions after Class 12. an also ensure their excellent performance in all other similar competitive exams with ease. The distinctive features of this series are = « The syllabus goes beyond the usual school syllabus to cover a wider aspect of the subject. e Textbook and Practice Material are present in a single book. A concise description of each topic with important concepts, definition and words. Important points at the end of each chapter giving brief summary of the concepts learned in the chapter. e Objective and Subjective Questions in each chapter based on the latest examination pattern. Challenging questions/problems solved for encouraging the students to come up with solutions of more tough questions/problems on their own. Exercises for practice with Simple Problems, Conceptual Problems, Multiple Choice Questions, Numerical Problems, Paragraph Questions, Assertion and Reasoning Questions, etc., as asked in the IIT entrance exams. The series hope to serve as a self-learning kit to the students which will give them the confidence to take up any entrance exam as a challenge. Any queries/suggestions regarding the subject matter can be sent to the publisher. We will strive our best to solve these queries and incorporate any suggestions given to us. Author© ismodaction © Classification of Mater © Classification of matter based on Physical sate + Kinetic Theory of Mater © Kinetic Theory of Matter and Solids ... 22 E (Chapter 3 : SYMBOLS, FORMULAE AND EQUATIONS « Introduction -- 32. Formulae of compounds Illustrations ... + Symbols of elements +. 32 Writing formulae by using valency : 34 of elements a * Let us have fun writing the formulae * Atomic Number 2 ae compounds * Jon + 34 . ; + Representing chemical changes — © Formation of cation 35 Chemical Equations * Formation of Anions +35 6 Balancing chemical equations © Valency of elements - 36 6 Radical © Molecule + 36» Important points to remember LAR WEIGHT . pena +45» Atomic Weight . i i toric Mass Uni “45° « Molecular Weight * Atomic Number and Mass Number... 45 Contents I ~y Separation of mixtures « Differences between compounds and mixtures iH ¢ Important points to remember 2131 (SIDUREDNNN Ghaper 2: stATES OF MATTER « Kinetic Theory of Matter and Liquids « Kinetic Theory of Matter and Gases Inter conversion of matter © Special terms used for conversion of sate Important points to remember * Calculating Molecular Weight 3244Chapter 5: ATOMIC STRUCTURE ag @ Introduction 51 © Fundamental Particles of Matter st « Daltom’s work with matter ot © Dalton’s proposals St « Dalton's arguments ose ¢ Why Dalton’s Theory is not accepted today . 52 « Modem Atornic Theory 8 + Main ideas of Mee temic Themny 53 © Atomic Number * Mass Number © Shells of an atom @ Valence electrons « Nucleons « Representing an element « Electronic configuration of elements (Bohr-Bury rules) © Introduction 9 * Acids 9 Asthenius Theory of Acids OB © Physical properties of acids B © Chemical propentics of wcids © Uses of acids + Bases © Alkalis 62 © Arthenius Theory of Bases 62 © Physical properties of bases « Chemical properties of bases « Uses of bases + Comparison of properties of acids and bases © Salts © Uses of salt -- 62 +» 62 + 62 + 62 ° Common names for acids and bases . Important points to remember -- 6 8 - B - 63 ¢ Introduction -- 6 « Paints © Useful metals + 6 o Fertilizers «© Glass +. 67 © Pesticides © Cement -- 67» Medicines © Plastics -- 68 Bio molecules «© Soaps and Detergents .. 68 © Important points to remember EE | Chapter 8 : AIR © Introduction +. 73» Importance of Atmosphere © Atmosphere + 73 « Air is matter zaz2esse . 74© Presence of mosetare = Composition of Air i ‘var ig mixture and not a compound. Th « hiv in necessary for burning : a of air 15 Aix and its ones : : Experiment to show composition of © Air composition is more oF leas costany oxygen and mitrogen in air «16g pix Pollution . + Presence of carbon dioxide +77, Smportant points to remember = e : Chapter 9: WATER ag + Introduction 85 « Physical Properties s # Why is water important? .. 85 « Hard and Soft Water - + Sources of water .. 85 « Importance of conservation of water. sy + Impurities present in water .. 86 © Pollution of water B + Water cycle .. 87» Types of water pollution ot + Need for potable water .-. 87 © Preventing pollution + Purification of water in labs . 87» Water-bome diseases 1 + Purification of water for drinking . 88 © Important points to remember 9 Chapter 10 CHANGES AROUND US 7-106 + Introduction - 97» Types of chemical changes 9 + Types of Changes- Physical + Chemical combination amd Cremical -97 . Pires gs + Chemical Decomposition * Chemical Displacement + Chemical change 97 : ? : ¢ Staly A ceaod S * Chemical double-decomposition 102 Chemica Reactions _. 98° T¥Pes of Chemical Reactions * Factors favoring chemical reactions ... 9g * IiPortant Points to remember 104 + Reschive substances1. Nature of Matter 2, Pure and Mixed Substances 43, Elements, Compounds and Mixtures 4, Symbols and Formulae 1. Elements Compounds and Mixtures 2. States of Matter 3, Symbols, Formulae and Equations 4, Atomic Weight and Molecular Weight 5, Atomic Structure 1. Action of Heat on Substances 2. Transformation of Substances 3, Symbols, Formulae and Equations 4, Types of Chemical Changes 5. Atomic Structure 6. Periodic Classification 7. Chemical Bonding 8. Water and Its Constituents 9. Hydrogen 1. Elements, Compounds and Mixtures 2. Symbols, Formulae and Equations 3. Gaseous State and Gas Laws 4. Atomic Strucutre 5. Changes Around Us 6. Water 7. Ait 6. Acids, Bases and Salts 7. Chemistry in Daily Life 8, Air 9, Water 10. Changes Around Us Class 8 10. Oxygen 11. Sulphur and Its Compounds 12. Nitrogen and Its Compounds 13. Study of Group IVA Element — Carbon and Its Oxides 14, Phosphorus and Its Compounds 15, Common Salt and Its Constituents 16. Metals and Non-Metals 5. Periodic Classification 6. Chemical Bonding 7. Chemical Kinetics 8. Chemical Equilibrium12, 14, Hydrogen Carbon 9, Study of Group IA Hlement 10, Study of Group IVA Hlement and Its Oxides 11, Study of Group VA LHlement and Its Compounds Nitrogen 1A, 4, a 1, Chemical Reaction (Part 1) 2, Chemical Reaction (Part 1) = 10. Mt. 12, 13, 3. Acids and Bases 4. Atomic Structure 5. Periodic Table and Classification of Elements 6. Chemical Bonding os Study of Group ViA Wenn “Yap, Study of Group VIA Hernan and He Compounds Mudy of Group VIA tie te WA iy One Wit Metal and Metallurgy Mevtrolysis Organic Chemistry Carbohydrates, Proteins, Vats and Oils Chemistry and Industry Analytical Chemistry Nuclear ChemistryELEMENTS, COMPOUNDS AND MIXTURES 4,0 INTRODUCTION ‘Any seionce is a systematic study by experimentation, observation and drawing inferences. Chemistry isa branch of seience that deals with a systematic study of the composition of matter and the reactions that take place between matter, A study of chemistry tells us how substances behave with other substances, It also explains about, how different chemical substances join together to form new substances For example, when wood is burnt it turns to ash with the release of hea and light, Some gas like carbon dioxide are also released, The burning of wood is a chemical reaction. In order to understand the nature of different I reactions, it Burning of wood chemical substances and chemica is important to know about the fundamental building blocks of all chemicals ~ the atom. 4.1 ATOM The word ‘atom’ comes from the Greek tomos” meaning indivisible, It was John Dalton, an English scientist, who proposed in 1808, that matter consists of very small particles called atoms, According to Dalton if matter is divided into smaller and smaller parts we will finally get a very small particle that cannot be divided any further, Dalton called the smallest particle of matter that was not divisible any further as an atom. word * Jolin Dalton ‘An English Sciontist Elements, Compounds and Mixtures Dalton studied matter and put forth his findings cd Dalton’s Atomic Theory. in a theory € Dalton’s Atomic 1, Matter is made up of tiny particles called heory atoms Atoms are indivisible, Atoms cannot be created or destroyed. 4, Atoms of the same element are identical in mass and other properties 5. Atoms of different elements differ in their masses and properties, 2 3 A pago from Dalton’s notebook, burnt in the bombing of Manchestor in World War Il particles called atoms that aro indivisibte. Further scientific studies showed that atoms could be divided further into still smaller ‘ording to Thomson, the atom was particles, A a positively charged solid ball with the negative electrons scattered inside it. Atoms are actually made up of negatively charged particles called electrons, positivelyerged and neutrally rtictes called protons aoe paricles called neutrons. 1.2 MATTER All materials around us are made of matter. Books, tables, chairs, the air we breathe, the water we drink, the food we cat, our body, the sun, the moon, the earth are all made up of matter. Let us define matter. Matter is anything that occupies space, has mass and can be perceived by our senses. Thus, there are three essential conditions for something to be called matter. They are as follows. 1, It must occupy space. 2. It must have mass. 3. We must be able to perceive it by our senses, i.¢., be able to touch, smell, see or taste it, We see so many different kinds of matter around us. Different kinds of matter differ from each other in their composition and properties, They differ in colour, size, weight, volume, composition, melting points, boiling points and solubility in water, Besides these differences, they differ from cach other in many ways. 1.3 CLASSIFICATION OF MATTER To study all the different kinds of matter accurately and con veniently, matter is classified into two broad categories: Pure substances and Mixtures, A pure substance con: ists only one kind. Examples Of particles of gold only; Particles of wai 2 of particles of Pure gold consists pure water contains, ler only, A mixture consists of particles of ing than one kind. Examples: salt solution eon particles of water and common is salt; 54 3 Suga solution contains particles of water and Ae! ir Discovery of electron 1, During the 1870: glish chemist and physicist Sir William Crookes developed the first cathode ray tube | 2. In 1874, the Irish physicist G J Stoney suggested that there existed a “singip definite quantity of electricity’. However, | Stoney believed these charges wers permanently attached to atoms and could not be removed. In 1894, Stoney | coined the term electron to represent these elementary charges. 3. In 1896, British physicist J J Thomson, performed experiments showing that cathode rays really were unique particles. Thomson called the cathode ray particles ‘corpuscles.’ 4. However, it was only at the end of the nineteenth century that these various concepts came together to form a unified theory based upon an electron as a fundamental component of matter. | Only later, Rutherford in 1911 and Neil | Bohr in 1912 and Chadwick in 1932 showed that all atoms are made ‘up of three particles ~electrons, protons and neutrons, Ce ad i] Classifying matter Matter is anything that occupies space, has mass and can be perceived by our senses. With this definition of matter in mind, can you identify different kinds of matter around you? Try to make a list of at least 20-25 different kinds of matter that you see around you.| Do you see any similarities between any of them? Try to group them according to some similarity that you can think of, into four or five groups, } Pure substances are further classified into ‘vo Sub-groups: Elements and Compounds. Goyal’ TIT Foundation Course = Chemistry for Class 7Matter + 1 + + Pure substances Mixed substances | (Mixtures) fomcarcaead Elements Compounds 4.4 PURE SUBSTANCES Pure substances contain particles of only one kind, Pure substances are further classified into Elements and Compounds. 4.5 ELEMENTS Elements are simple pure substances made up of only one kind of particles that cannot be decomposed or divided any further into simpler | chemical substances. Examples: Oxygen, nitrogen, carbon, hydrogen, iron, copper, gold, silver. Characteristics of elements ‘An element has the following important characteristics () An element is made up of atoms of only one kind. It has uniform composition — in other words elements are homogeneous in nature. The atoms of an element are all identical They differ from the atoms of other elements eo ©0@ = _, 68 _,9 08 6 "@O0 o © Apiece of zinc 6 e200 ‘Smaller pieces of zinc Atoms of zinc (ii) An element cannot be broken by chemical methods or physical methods into simpler substances. (iii) An element has specific physical properties like physical state, density, colour, odour, taste, melting point and boiling point. (iv) Ancelement has specific chemical properties like reactivity with other substances. (v) An element occurs either in the free state as free element or in combination with other elements as a compound. Mlustration: A piece of aluminium sheet contains only aluminium atoms. Aluminium cannot be broken or decomposed by chemical methods into any simpler substances. Similarly, a wire made of copper contains atoms of copper only and can be decomposed by chemical methods into simpler substances, Number of Elements Known At present, around 116 elements are known. Out of these around 92 occur naturally in the earth’s crust while the rest are artificially created by man. 1. At ordinary room temperature, most elements are solids. 2. One element — Mercury is a liquid. 3. There are eleven elements that are gases— Hydrogen, Helium, Oxygen, Nitrogen, Fluorine, Neon, Chlorine, Argon, Krypton, Xenon and Radon. . More than 80 elements are metallic elements while around 22 are non-metallic elements. . Some elements are radioactive elements as they emit radiation which is often harmful. Distribution of elements in the earth’s crust All the elements do not occur in nature in equal abundance. Some elements like oxygen, silicon, aluminium, iron, calcium are more abundant than the other elements. About 90% of the earth’s crust is made up of these five elements, Abundance of elements in the universe Elements like hydrogen and helium are the | main elements present in the sun and stars. Hydrogen is the most abundant element in the universe. Classification of Elements Based on their properties, the elements are classified into four groups as follows. (A) Metals (82). (B) Non-metals (22). (C) Metalloid (7). (D) Noble gases (6). Elements, Compounds and MixturesNon-metals are more abundant in the earths crust than metals, ’ Oxygen is the earth's crust, Aluminium is the clement in the ‘Technetium clement. A. Motals Of all known elements Soh ntmPles: Iron, Copper, Silver, Gold Sodium, Lithium, Potassium, Calcium, Zing te Metals have specific properties (see boxes), Physical Properties 1, Metals are temperature, Most abundant element in the Most abundant metallic earth's crust, (Te) is the first’ man-made ——___ about 80% are metals, generally solids at room Only mercury is a liquid at room temperature (25°C), 2. They have luster or shine when cut 3. They can be beaten into thin sheets - this Property is called malleability, 4. They can be drawn into wires — this Property is called ductility, Physical Properties Every pure substance has a set of physical Properties that are unique to that substance, This set of physical properties is often used to identify the substance, Some physical properties are given below. 1. Physical state at room temperature 2. Colour, smell and taste 3. Solubility in water 4. Density 5. Hardne: 6. Thermal conductivity 7. Electrical conductivity 8. Melting point 9. Boiling point etc. 5. They are good conductors of heat and electricity (Lead is an exception, Lead is a poor conductor of heat) 6. Metals have high boiling point and melting point. ~ Goyal’s IIT Foundation Course — Che oo 7. Metals make a sound when struck - are sonorous substances, 8. Metals are hard and cannot be cut with 4 knife, (The exceptions are sodium Potassium, Calcium as they are soft and ‘an be cut with a knife), 9. Metals have high density (Lithium, Sodium, Potassium and calcium arg exceptions as they have low densit Lithium has the lowest densit metals), ~ they 'Y amongs Chemical Properties Metals react with other sul 1. Reaetion with oxygen Many metals react with oxygen forming metallic oxides. Example: A burning piece of magnesium s with oxygen forming magnesium nces as follows: Mg + 0, MgO 2. Reaction with water Many metals react with water or steam to form metal hydroxide and liberate hydrogen, Example: A sodium piece when put n water reacts vigorously liberating hydrogen. The solution that forms when the reaction stops is soapy to touch, 2Na + 2H,O— NaOH + Ht 3. Reaction with acids Many metals react with dilute acids liberating hydrogen gas Some metals like gold, silver and platinum do not react with dilute aci Example: Zine reacts with hydrochloric acid forming zine chloride and hydrogen Zn + 2HCI> ZnCl, + Ht B. Non-Metals There are about 22 non-metals that are known, Bromine is the only non-metal which is liquid at room temperature. Other non-metals at room temperature Oxygen and silicon are the most abundant elements that are non-metals, They constitute about 75% of the earth's en Examples: Carbon, Oxyge ilphur, Chlorine ete, Nitrogen, nisiry for Class 7 aee ical Properties Non-metals exist in all three physical states. For example, hydrogen, chlorine and oxygen are non-metals that are gases. Bromine is a non-metal that is a liquid. Todine, sulphur and carbon are non-metals that are solids. Non-metals are brittle. They break into pieces when hammered. / Non-metals are non-duetile as they break on stretching. 4, Non-metals are bad conductors of heat and electricity. The only exception is graphite which is a non-metal but a good conductor of electricity. . Non-metals do not shine. They are not phys! L Chemical Properties Non-metals react with other substances as follows. 1. Reaction with oxygen Many non-metals react with oxygen forming non-metallic oxides. Example: Carbon burns in air combining with oxygen forming carbon dioxide. C +0, CO, 2. Reaction with water Some non-metals react with water while many do not. Example: Chlorine reacts with water forming a mixture of acids. Cl, + H,0- HCI + HCIO 3. Reaction with acids Some non-metals react with concentrated 5. lustrous. But, graphite and iodine are nitric acid. exceptions as they are non-metals with Example: When carbon is put in luster. concentrated nitric acid it liberates two 6, Non-metals are generally soft. The only gases and water. exception is diamond which is very hard. C + 4HNO,> CO, + 4NO, + 2H,O 7, Non-metals are non sonorous. Comparison of metals and non-metals 8, Non-metals have low melting point and ‘The physical and chemical properties of boiling points. The exceptions are diamond | metals and non-metals are compared below. and silicon as they have high melting and | Some of the exceptions to each property are boiling point. also given where they are present. Physical Properties Properties Metals Non-Metals 1. Physical state | ceptions: Mercury Generally solid at room temperature (25°C). Gases, liquids or brittle solids Exceptions: Diamond, Silicon 7. Conductivity Exceptions: Zine, Arsenic cHaraness [SO Parl Generally soft : Exceptions: Sodium, Potassium, Calcium | Exceptions: Diamond 3. Lustre te me fe ea) ines [oe : Exception: lodine and graphite A High Low | 4. Density Exception: Sodium, potassium, calcium | Exception: Diamond 5. Melting point | High eS : and Exceptions: Sodium, potassium have low MP, | Boiling point | while Gallium, mercury have low BP 'xception: Carbon, Silicon 6 Malleability / |High malleability and ductility. Non-malleable and not ductile Ductility | Exceptions: Zine, Arsenic, Mercury Exception: Carbon fibre High Poor Exception: Graphite Elements, Compounds and MixturesChemical Properties Metals . “Form metallic oxides at 2 Reaction with water | Liberate hydrogen [3 Reaction with acids | Liberate hydrogen C. Metalloids 1. Reaction with OXYBE" | sotids and basic in nature are | Form non-metallic oxides that gascous and acidic in nature Only a few There are some elements that show the | in several ways, ies of both metals and non-metals. re metalloid clements are Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te) and Pollonium (Po). D. Inert gas elements or noble gases There are six clements that do not react with other elements. They are all gases, These elements are found in air in small quantities, Due to their non-reactive nature they are called noble or inert gas elements, The elements that are inert gas elements are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn), Representing elements in short form — Symbols of Elements With so many elements existing either in the free state or in the combined state with other elements, it would be more convenient if we could represent these elements- in the free state or in the combined state in a short form. When we use the letters PTO at the end of @ page we know that it stands for ‘please turn over.’ We turn the page and continue to read when we come across these words. Similarly, we use the short form etc. at the end of a list of things. This is short form for etcetera which (a) For some Symbols for different element: Non-Metal: non-metals react with water “| Hydrogen is not liberated | Hydrogen is not liberated Hydrogen isnot liberated. Onlya few now | metals react with concentrated Nitric acid. elements the first | etter of the name of the element is taken are often 'S are selected Examples: Element Symbol | Element Symbol Hydrogen H | Carbon c | Oxygen O | Fluorine F | Nitrogen No Phosphorus p | Sulphur s (b) For some eleme: of the name of nts the first two letters the element are taken, Examples: Element __ Symbol [Element Symbol Calcium Ca |Germanium Ge Helium He | Argon Ar Aluminium Al | Neon Ne | Silicon Si_| Nickel Ni (©) For some eleme based on sound. nts the symbol is taken Examples: Element Symbol | Element Symbol Magnesium Mg [Manganese Mn (d) For some elements are taken from theit Latin names, means that there are other items in the list. Element Latin name Symbol Another short form that we use often is e.g., | [Sodium Natrum ‘Na which stands for example. Potassium | Kalium K Elements can be represented using a standard | | Lead Plumbum Pb list of symbols or short form representations. — | | Iron Ferrum Fe A symbol is a short form representation of Silver Argentun Ag an element. Copper Cuprum Cu Example: H is the symbol for Hydrogen; 0. | | Gold Aurum Au is the symbol for Oxygen, etc. Antimon Stibium Sb 6 Goyal’ IIT Foundation ‘Course — Chemistry for Class 7 — ——= symbols convey very useful information shout the element they represent. For example, the symbol H used for the element hydrogen conveys the following jnformation: {i) The symbol H is ofthe element hydrogen. (i) The symbol H represents one atom of hydrogen. similarly, the symbol O used for the element exygen conveys the following information: {i) The symbol O is of the element oxygen. (ii) The symbol O represents one atom of oxygen. Elements are made up of atoms Elements are pure substances that are made of small particles called atoms. “Atoms are the smallest particles of matter that may or may not exist independently and take part in chemical reactions. The structure of the atom is as follows. 1. The atoms have electrons, protons and neutrons in them. (i) The electrons are negatively charged particles. (ii) The protons are positively charged particles. (iii) The neutrons are neutrally charged particles, ‘The number of electrons is equal to the number of protons. Since the negatively charged particles (electrons) are equal to the positively charged particles (protons) the atom is neutral. The protons and neutrons are present in a small central region called the nucleus. The electrons revolve around the nucleus at high speeds. The Atomic Number of an element gives the number of protons in the atom. This number is equal to the number of electrons in the neutral atom. For example, the Atomic number of sodium is 11. This means that each sodium atom has !1 protons and 11 electrons. Similarly, the ‘Atomic number of oxygen is 8. This means that each oxygen atom has 8 protons and 8 electrons. Elemenis, Compounds and Mixtures 6. The electrons revolve around the nucleus in orbits of increasing radius. 1.6 COMPOUNDS Elements exist in free state as well as in combined state. When elements exist in the combined state, it is actually the atoms of the elements that combine to form what Dalton called ‘compound atoms’, We call the combined state of elements as compounds. ‘A compound is a pure substance formed by the chemical combination of atoms of the same or different elements in a fixed ratio by mass. Example 1: Chalk is a compound made up of atoms of calcium, carbon and oxygen combined in the ratio 10 : 3 : 12 by weight. Example 2: Water is a compound made up of atoms of hydrogen and oxygen combined in the ratio 1: 8 by weight. Example 3: Carbon dioxide is a compound made up of atoms of carbon and oxygen combined in the ratio 3:8 by weight. Thus, a compound is made up of two or more molecules of one or more elements combined chemically in a fixed proportion by weight. Compounds have specific physical properties like physical state, density, colour, odour, taste, MP and BP. They also have specific chemical properties like reactivity with other substances. The physical and chemical properties will be different from those of the elements in the compound. Characteristics of compounds ‘A compound has the following important characteristics (i) Compounds have a uniform composition— in other words they are homogeneous in nature. The properties of compounds are different from those. of its constituent elements. Compounds can be broken down into their constituent elements by chemical methods but not by physical methods like boiling, distilling etc. Compounds have a fixed composition of their own. Gi) (iii) (iv)(v) Energy is cither absorbed or released during the formation of a compound. (vi) A compound can be represented by its formula. Molecules Molecules are the smallest particles of a substance that can be an element or a compound that can exist independently and are made up of two or more atoms combined chemically in a fixed proportion by weight and exhibit all the properties of that substance. Example 1: Water molecule (i) Each molecule of water consists of two atoms of hydrogen and one atom of oxygen. (ii) The two elements hydrogen and oxygen are combined in a ratio of 1:8 by weight. (iii) A water molecule can exist independently. Example 2: Sulphur dioxide molecule (i) Each molecule of sulphur dioxide consists of one atom of sulphur and two atoms of oxygen. (ii) The two elements sulphur and oxygen are combined in a ratio of 1:1 by weight. (ii) A sulphur dioxide molecule can exist independently. Example 3: Hydrogen molecule (i) Each molecule of hydrogen consists of two atoms of hydrogen. (ii) The two atoms are combined chemically. A hydrogen molecule can exist independently. Two atoms of hydrogen join to form one molecule of the element hydrogen -@-> Examples : H, ~ Hydrogen molecule is formed when atom of Hydrogen combine chemicaiy ©, = Oxygen molecule is formed when 97 atom of Oxygen combine chemically "” N, — Nitrogen molecule is formed when ry, atom of Nitrogen combine chemie ~ Sulphur molecule is formed when ¢j atoms of Sulphur combine chemicaly P, ~ Phosphorus molecule is formed yy, four atoms of Phosphorus combic, chemically. a. Molecules of Element (we) ally, inc Gold Copper Hau Hydrogen Chlorine Nitrogen Oxygen | Molecule Molecule Molecule Molecule Ozone Molecule Heteroatomic molecules are formed by atoms belonging to different elements. Examples: NH, - Ammonia molecule is formed when one atom of Nitrogen combines chemically with three atoms of Hydrogen. H,0 - Water molecule is formed when two atoms of Hydrogen combines chemically with one atom of Oxygen. CO, - Carbon dioxide molecule is formed when * one atom of Carbon combines chemically with two atoms of Oxygen. @-©:@-G28 1 Molecule of 1 atom 1 atom 1 molecule 1Atom: 4 Atom 1 Atom Maio o of hydrogen of hydrogen carbon aus ae Formation of Carbon Dioxide — Two atoms of x80" Molecules are of two types. combine chemically with one carbon atom t0 form 0! Molecule carbon dioxide molecule pant wg Molecule ge Hydrogen Water Zinc oxide soar Homoatomie molecules are formed by atoms Sede, molecule molecule cam mol e Jecule Molecules of compoun' belonging to the same element. mol Molecu ein ast Goval’s HF Foundation Course — Cher wai BAtomic omussonis molocales xe sade up of aterm of uy one Cement Atomictty bs the number of sioms of an dement present in one mudecule of the clement. Depending upon atomicity, homente cements ae called (2) Monuatmnie, if ony in the mohecle of Lxamples: Hel Copper (Cx) Diatomie, if two aon prevent in the molecule of the Examples: Sydrogen (H.), Chlorine (C1) ‘Triatombe, if three aums of the element ane present in the molecule of the element. Examples: Orone (O.) Polyatomic, if three atoms of the element ase prevent in the molecule of the element. jar (S,) ome, si 3 peevent ernect. (Hi ) a) ) Fiamciome | mriherzites, Ph) Representing elements in short form - Formula Just as symbols arc used to represent elements in short form, a chemical formula is used to represent % compound in short form. Siucaute of 4 sulphur meas, Se Formulae of some metallic oxides Metallic oxides | ___—‘Formula Magnesium oxide MgO) | Calcium oxide [C20 Zine oxide ZnO Copper oxide Cu) Formulae of some common metallic sulphides Elements that do not combine Atoms of metals and metalloids do not combine with their own types of atoms. Similarly, the atoms of inert gases exist free under all conditions. So their atoms are regarded as molecules, The molecules of all these elements are said to be monoatomic molecules. A formula is a short form representation of « compound. To write a formula, the symbols of all the clements are written close together with small subscripts that show the number of atoms of that clement that have combined chemically. Elements, Compounds and Mixtures Metallic sulphide Formula jesium sulphide | MgS [Zine sulphide ZnS [Iron sulphide FeS Calcium sulphide CaS Naming of compounds ‘A few examples of how compounds are named are given below. (i) Metal + oxygen — metallic oxide Zine + oxygen — Zinc oxide Non-metal + oxygen — non-metallic oxide Sulphur + oxygen — sulphur dioxide (ii)——— (i) Bloment + chlorine» ehtoride Clwvaitication of mistures based on the Zine + ehlorine > eine chloride of matter Mate Hywtrygen + chlorine > hydrogen ebloride 1, Huved on the physieal state: n4 (iy) Bloment + autphur > sulphide ave the classified based on the physical su" ine + sulphur» gine sulphide the constituent parts mate of 1.7 MIXTURES (a) Solld-solld mixture A mixture isa substance made up of two oF I a mixture contains two sotigy yore elements oF compounds mixed together in components then it is called solid — yy & random proportion mixture : Example Ly Salt solution is a mixture of Example 1: A mixture of pebbles common salt and water The amount of salt ean pulses — both pebbles and pulse yan be increased or decreased, Similarly, the amount are solids, 3 ‘of water can be increased or deorsqsed. Example 2: A mixture of iron and sang Example 2: Brass is a mixture of copper both iron and sand are solids and zine (b) Solid ~ liquid mixture _ Example 3: Glucose solution ix. a mixture Wa mixture contains a solid and liquid a of glucose and water, components, it is called a solid ~ liquig Example 4: Air is a mixture of gases-mainly mixture nitrogen, oxygen, carbon dioxide and water le 1: A mixture of clay and water vapour is a solid mixed in water which js Types of mixtures a Liquid Mixtures are classified into two types Example 2: A mixture of chalk and water depending upon their composition. = chalk is a solid mixed in water which ’ is a liquid + ample 3: A mixture of common salt in Homogeneous Heterogeneous sea water — common salt is a solid mixed Example 1: Sugar solution is a mixture of in sea water which isa liquid sugar and water that has a uniform composition | (€) Liquid ~ liquid mixture throughout the solution. If a mixture contains two liquids as Example 2: Petrol is a mixture of hydrocarbon components, it is called liquid ~ liquid fuels that has uniform composition throughout. mixture, Example 3: Brass is a mixture of copper and Example 1: A mixture of oil and wate zine that has uniform composition throughout. oil and water are liquids : Example 2: A mixture of methyl alcohol Homogeneous mixture a and ethyl aleohol ~ both are liquids A homogeneous mixture has uniform iy Soild ea ais composition throughout the mixture. Ce ea tare Ifa mixture contains a solid mixed with « Heterogencous mixture - cous substance, itis called a solid A heterogeneous mixture has different aoa eee composition in different parts of the mixture, ae ee Example 1: A mixture of sand and water reaps, Smee 8 eae has different composition in different parts of ee cena (©) Liquid = gas mixture i Example 2: A mixture of iron and sulphur a Neale arse ire has different composition in different parts of a gaseous substance, itis called a lig aria gas mixture. 10 Goyal’ HIT Foundation Course — Chemistry Jor Class 7 — i