Atoms & Molecules

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SCIENCE PROJECT :

☣ ATOMS & MOLECULES ☢ SCIENCE PROJECT Session: 2013-14 Kendriya Vidyalaya No.1 ,Harni Road ,Vadodara

Atoms and Molecules:

Atoms and Molecules An Indian philosopher Maharish Kanad , postulated that if we go on dividing matter (Padarth), we shall get smaller and smaller particles. He named these particles Parmanu . Around the era , ancient Greek philosophers – Democritus and Leucippus suggested that if we go on dividing matter , a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms (meaning indivisible).

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Law Of Conservation Of Mass :- Law of conservation of mass states that mass can neither created nor destroyed in a chemical reaction. Law Of Constant Proportions :- In a chemical substance the elements are always present in definite proportions by mass. Laws Of Chemical Combination :- The two laws of chemical combination were established after much experiments by Lavoisier and Joseph L. Prous .

John Dalton:

John Dalton John Dalton was born In a poor family in 1766 in England. He began his career as a teacher at the age of twelve. Seven years later he became a school principal. In 1793, Dalton left for Manchester to teach mathematics, physics and chemistry in a college. He spent most of his life there teaching and researching. In 1808, he presented his atomic theory which was turning point in the study of mater.

Dalton’s Atomic Theory:

According to Dalton’s atomic theory , a matter, whether an element, a compound or a mixture is composed of small particles called atoms. The postulates of this theory may be stated as follows: All maters is made up of very tiny particles called atoms. Atoms are indivisible particles, which cannot be created or destroyed in chemical reaction. Atoms of a given element are identical in mass and chemical properties. Atoms combine in the ratio of small whole numbers to form compounds. The relative number and kinds atoms are constant in a given compound. Dalton’s Atomic Theory

Dalton was the first scientist to use the symbols for elements in a very specific sense. When he used a symbol for an element he also meant a definite quantity of that element, that is, one atom of that element. Berzelius suggested that the symbols of elements be made from one or two letters of the name of the element.:

Dalton was the first scientist to use the symbols for elements in a very specific sense. When he used a symbol for an element he also meant a definite quantity of that element, that is, one atom of that element. Berzelius suggested that the symbols of elements be made from one or two letters of the name of the element. The name copper was taken from Cyrus . Gold was taken from the English word meaning yellow . The name iron was taken from its Latin name ferrum . IUPAC (International Union Of Pure And Applied Chemistry) approves names of elements.

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What is an Atom? Atom is the smallest particle which is not independent. Atomic radius is measured in nanometers. How Big Are Atoms? Atoms are very small , they are smaller than anything that we can imagine or compare with. More than millions of atoms when stacked would make a layer barely as thick as the sheet of paper. 1/10⁹m = 1 nm 1 m = 10⁹ nm We may not be able to see them, but they are there, and constantly affecting whatever we do.

Atomic Mass:

Atomic mass may be defined as: The relative mass of an atom of the element as compared to an atom of carbon taken as 12. In other words, atomic mass expresses the number of times an atom of the element is heavier than a carbon atom taken as 12 or 1/12 th of the mass of carbon atom. Therefore, Atomic mass = Mass of an atom 1 /12 th mass of a carbon atom (carbon-12) Atomic Mass Unit :- The quantity of mass equal to 1/12 th of the mass of an atom of carbon is called atomic mass unit. How do atoms exist? :- Atoms of mostly elements are not able to exist independently. Atoms form molecules and ions. These molecules or ions aggregate in large numbers to form the matter that we can see, feel or touch. Atomic Mass

What Is A Molecule?:

A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance. Atoms of the same element or of different elements can join together to form molecules. Molecules of elements :- The molecules of an atom element are constituted by the same type of atoms. The number of atoms constituting a molecule is know as its atomicity. Molecules of compound :- Atoms of different join together in definite proportions to form molecules of compounds. What Is A Molecule?

What Is Ion?:

An ion is a charged particle having negative or positive charge. A negatively charged ion is called ‘anion’ and the positive charged ion, a ‘cation’. Take, for example, sodium chloride (NaC1). Its constituent particles are positively charged chloride ions(Na*) and negatively charged chloride ions (C1-).ions may consist of single charged atom or a group of atoms that have a net charge on them. A group of atoms carrying a charge is know as a polyatomic ion . What Is Ion?

Writing Chemical Formulae:

The chemical formulae of a compound is a symbolic representation of it composition. The chemical representation of its composition. The combining power (or capacity) of an element is known as its valency. Valency can be find out how the atoms of an element will combine with the atom(s) of another element to form a chemical compound. The valency of the atom of an element can be thought of as hands or arms of that atom. Writing Chemical Formulae

Formulae Of Simple Compounds:

The simplest compounds, which are made up of two different elements are called binary compounds. While writing the chemical for compounds, we write the constituent elements and their valencies as shown below. Then we must crossover the valencies as shown below. 1) Formula of hydrogen chloride:- Symbol H C1 Valency 1 1 Formula of the compound would be HC1. 2) Formulae of hydrogen sulphide:- Symbol H S Valency 1 2 Formulae: H ₂ s Formulae Of Simple Compounds

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3) Formulae of carbon tetrachloride:- Symbol C C1 Valency 4 1 Formulae: CC1 ₄ For magnesium chloride we write symbol of cation (mg ² +). The positive and negative charges must balance each other and the overall structure must be neutral. Note that in the formulae, the charges on the ions are not indicated. Symbol Mg C1 Charge 2+ 1- Formulae:MgC1 ₂ Thus, in magnesium chloride, there are two chloride ions(C1-) for each magnesium ion (Mg ² +). The positive and negative charges must balance each other and the overall structure must be neutral. Note that in the formulae, the charges on the ions are indicated.

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a) Formulae for aluminum oxide:- Symbol A1 O Charge 3+ 2- Formulae: A1 ₂ O ₃ b) Formulae for calcium oxide:- Symbol Ca O Charge 2+ 2- Formulae: Ca ₂ O ₂. But we simplify the formulae as CaO. c) Formulae of sodium nitrate:- Symbol Na NO ₃ Charge 1+ 1- Formulae: NaNO ₃ d) Formula of calcium hydroxide:- Symbol Ca OH Charge 2+ 1- Formulae: Ca(OH) ₂

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e) Formula of sodium carbonate:- Symbol Na CO ₃ Charge 1+ 2- Formula: Na ₂ CO ₃ In the above example, brackets are not needed if there is only one ion present. f) Formula of ammonium sulphate:- Formula NH ₄ SO ₄ Charge 1+ 2- Formula: (NH ₄ ) ₂ SO ₄ MOLECULAR MASS :- The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance. Relative molecular mass = mass of 1 molecule of the substance 1/12 * mass of one C-12 atom

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The molecular mass of a molecule, thus , represents the number of times it is heavier than 1/12 the mass of a carbon – 12 isotope. Calculation of molecular mole: the molecular mass of a substance is the sum of the atomic masses of its constituent atoms present in a molecule 1. Molecular mass of the water the molecular formula of water is H2O atomic mass of H=1 Atomic mass of O=16 • Molecular mass of water = (2x atomic mass of H)+(1x atomic mass of O)= 2x 1+116 = 18 i.e., molecular mass of water = 18 amu.

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2. Molecular mass of sulphuric acid = The molecular formula of sulphuric acid is H2SO. Atomic mass of H =1 Atomic mass of O =16 Atomic mass of S = 32 • Molecular mass of H2SO4 = (2x atomic mass of H)+(1x atomic mass of S)+(4x atomic mass of O) = (2 x 1)+(1 x 32)+(4 x16) = 2+32+16 = 98 i.e., molecular mass of H ₂ SO ₄ = 98 amu.

Molecule Concept:

The word “mole” was introduced around 1896 by Wilhelm Ostwald who derived the term from the Latin word moles meaning a ‘ heap’ or ‘pile’. A mole of atoms is a collection of atoms whose total mass is the number of grams equal to the atomic mass. Since an equal number of moles of different elements contain an equal number of atoms, it becomes convenient of express the amount of the elements in the terms of moles. A mole represents a definite number of particles, viz., atoms, molecules, ions or electrons. This definite number is called the Avogadro number (now called the Avogadro constant) which is equal to 6.022 x 10²³. Avogadro constant = 6.022 x 10²³ A mole is defined as the amount of substance that contains as many atoms , molecules, ions, electrons or other elementary particles as there are atoms in exactly 12g of carbon - 12(¹²C). The mass of 1 mole of atoms of an element is its relative atomic mass taken in grams. Molecule Concept

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Prepared By :- $ .AKASH

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