Chapter 1 - Matter in Our Surroundings. Chapter 2 - Is Matter Around us Pure. Chapter 3 - Atoms and Molecules. Chapter 4 - Structure of Atom. Chapter 5 - The Fundamental Unit of Life. Chapter 6 - Tissues. Chapter 7 - Diversity in Living Organisms. Chapter 8 - Motion.
Chapter 9 - Force and Laws of Motion. Chapter 10 - Gravitation. Chapter 11 - Work and Energy. Chapter 12 - Sound. Chapter 13 - Why do We Fall ill. Chapter 14 - Natural Resources. Chapter 15 - Improvement in Food Resources. Following these NCERT solutions will help you get an insight into all the concepts covered in this chapter. There are two laws of chemical combination- the law of conservation of mass, and the law of constant proportion.
Both these laws are discussed in detail in chapter 3, science class 9. There is one important question related to the chemical reaction. Is there any change in the total mass of the system when a chemical reaction takes place?
According to the law of conservation of mass, mass can neither be created nor be destroyed. The same logic stands true for chemical reactions as well. Several experiments carried out by Lavoisier standardized this law.
The law of chemical combination is based on another law- the law of constant proportion. This law was also the result of experiments conducted by Lavoisier and Joseph L.
According to the law of constant proportion, any compound is made by mixing two or more elements in a constant proportion, and this proportion does not change irrespective of the source of the compounds.
For example, in water, the ratio of the mass of Hydrogen to the mass of Oxygen is The ratio of the mass is the same for water from different sources. This law is also known as the law of definite proportion. The law of constant proportion is explained thoroughly in Class 9 Science Chapter 3.
The issue that the scientist faced with the law of constant proportion is to provide a possible explanation for this. Eminent scientist John Dalton tried to provide an explanation and introduced the concept of atoms.
An atom is the smallest unit of matter. They are so small that thousands of them are stacked in your hair. The atom of one element is different from that of the other elements. Therefore, each of these atoms is depicted by different symbols. Dalton used different combinations of straight lines and circles for denoting various atoms. However, the modern-day symbols consider the first or the first two letters of the element's name to denote an atom of the element. For example, Hydrogen is denoted by H and Oxygen by O.
In some cases, and the Latin names are also considered. For example, the Latin name of Potassium is Kalium, and it is denoted by K. A list of names of elements is shown in Atom and Molecules Class 9. Every atom has a definite mass, called the atomic mass unit. The atomic mass is the characteristic of the atom. The concept of atomic mass supports the law of constant proportion and the law of conservation of mass. However, atoms cannot exist freely in nature.
It interacts with the same or different atoms to form molecules. They can also form ions. These ions or molecules aggregate to form elements of compounds that we can see. These concepts are covered in Ch 3 Science Class 9. A group of two or more atoms is joined together to form a molecule.
A molecule can exist freely in nature. For example, Hydrogen, Oxygen, Calcium molecules can exist freely in nature. Molecules can be created from the same atoms or different atoms. If the molecules are made from the same kind of atoms, they are called molecules of elements. For example, Sodium and Potassium elements. Molecules can also be made from dissimilar atoms. When different atoms come together, they form a compound. The molecules made of different atoms are called molecules of compounds.
Sometimes, the atoms can be charged. Charged atoms are called ions. An ion can always be charged positively or negatively charged.
Positively charged ones are known as cations, while negative ones are known as anions. Sometimes, a molecule can contain more than one ion. Such molecules make a polyatomic ion. The individual charges on each atom determine the net charge of such ions. To learn more about polyatomic ions, go through Class 9 Science Chapter 3. The symbolic representation of the compounds is said to be their chemical formulae.
The chemical formula considers the net charge of individual ions in the formula. The charge of individual ions determines the valency of the radical. The valency of the individual ions determines how many ions of a particular kind will take part in the interaction.
For the proper representation of the chemical formula, the valency of individual ions must be balanced. The metal names should come before any non-metal name. In the case of polyatomic ions, the individual elements must be kept in a bracket if their overall valency is more than one. Otherwise, there is no need to use a bracket�for example, NaOH.
The molecular mass of a compound is the sum of all the atomic masses. Therefore, the molecular mass is represented in atomic mass units. Read NCERT solutions for class 9 science chapter atoms and molecules to learn more about molecular mass. Formula unit mass is calculated similarly to molecular mass.
Learn more about formula mass units in ch 3 science class 9. Mole concept is another important concept related to atoms and molecules. It defines the total number of molecules taking part in a chemical reaction.
You can learn the mole concept in detail in Atoms and Molecules Class 9. Exercise 3. Chapter 3 Science Class 9, is presented comprehensively. The pointwise approach of chemistry ch 3 class 9 NCERT solutions help students revise the chapter before the examination.
The topics covered in ch 3 science class 9 become easily understandable when students go through the atoms and molecules class 9 NCERT solutions.
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