CHAPTER 4 STRUCTURE OF ATOM
J.J Thomson came up with a model to explain the structure of atom. According to this model, the atom consists of a positively charged sphere in which the negatively charged particles i.e. electrons are embedded. The positive charges and negative charges are equal in magnitude which makes the atom neutral.
Rutherford conducted an alpha particle scattering experiment using a gold foil. α- particles are doubly charged helium ions. In the experiment, fast moving α- particles are made to fall on a thin gold foil. Fast moving α- particles have high energy. It was expected these particles would get deflected due to the negative charged particles in the atom.
Observations made after the experiment:
Drawbacks of Rutherford’s model:
Any particle moving in a circular orbit would undergo acceleration, lose energy and eventually fall into the nucleus. This would result in the atom being highly unstable. Therefore, this model could not explain the stability of atom.
This model states that only certain orbits of electrons are allowed inside the atom. While revolving in these orbits, the electrons do not lose energy. These orbits are called energy levels and are represented by the letters K, L, M, N… or 1,2,3,4...
NEUTRONS: A neutron is a sub-atomic particle present in the nucleus. It has no charge and its mass is nearly equal to that of a proton.
Rules for distributing electrons into different orbits:
The number of protons present in the nucleus of an atom is called the atomic number of the element. It is denoted by ‘Z’.
Protons and neutrons together are known as nucleons. The number of neutrons and protons i.e. nucleons present in the nucleus is called the mass number.
Isotopes are the atoms of an element having the same atomic number but different mass numbers.
Atoms of different elements with different atomic numbers having same mass number are called isobars.
CHAPTER 3 ATOMS AND MOLECULES
LAWS OF CHEMICAL COMBINATION
There are two laws of chemical combination:
DALTON’S ATOMIC THEORY
The postulates of this theory are:
An atom is the building block of all matter. The size of an atom is very, very small. In fact, the radius of an atom is around 1 nm i.e. 10-9 m.
Atomic Mass: One atomic mass unit(amu) is equal to 1/12th the mass of one atom of carbon 12.
A molecule is a group of two or more atoms held together by attractive forces. For e.g. CO2 is a molecule of carbon dioxide.
The charged particles in substances are called ions. A positively charged ion is called a cation and a negatively charged ion is called anion. For e.g. HCl contains H+ ions and Cl- ions.
The chemical formula of a compound is determined by the valency of each element.
For e.g. The valency of H is 1 and that of S is 2. The valencies are exchanged and the formula becomes H2S.
The molecular mass is the sum of the atomic masses of all the atoms in the molecule.
FORMULA UNIT MASS
The formula unit mass is the sum of the atomic masses of all atoms in a formula unit of the compound.
One mole of a substance is that quantity which has mass equal to its atomic or molecular mass in grams.
The number of particles present in 1 mole of any substance is constant i.e. 6.022 x 1023. This value is known as Avogadro’s Constant (N0).
The mass of 1 mole of a substance is called molar mass.
CHAPTER 2 IS MATTER AROUND US PURE?
A mixture is a combination of more than one pure substance.
Types of mixtures:
Homogeneous mixture: When a mixture has a uniform composition throughout, it is known as a homogeneous mixture.
Heterogeneous mixture: When a mixture has a non-uniform composition, it is known as a heterogeneous mixture.
A solution is a homogeneous mixture of two or more substances.
A solvent is the liquid which is used to dissolve a substance. A solute is the substance that is dissolved in the solvent.
A solute and a solvent together form a solution.
Properties of a solution:
Concentration of a solution
At any temperature, a solution is said to be saturated if there is as much solutes dissolved in it as it is capable of dissolving. If the amount of solute contained in the solution is less than the saturation level, the solution is said to be unsaturated.
Concentration of a solution is the amount of solute present in a given amount of solution.
Concentration of solution= (Amount of solute)/(Amount of solution)
Mass by mass % of a solution= (Mass of solute)/(Mass of solution) X 100
Mass by volume % of a solution=(Mass of solute)/(Volume of solution)
A heterogeneous mixture in which the solute particles do not dissolve but remain suspended in the solution. These particles are visible to the naked eye.
The particles also scatter a beam of light passing through it. The solute can be separated from the solvent by filtration.
The particles of a colloid are uniformly spread throughout the solution. It is a heterogeneous solution. The particles are smaller than the particles in a suspension and do not settle down when the solution is left undisturbed. These particles cannot be seen with naked eyes and they also scatter the beam of light passing through the solution. This scattering is called Tyndall Effect.
The solute particles are called dispersed phase and the solvent is called the dispersion medium.
Pure substances can either be elements or compounds.
An element is s substance that cannot be broken down into simpler substances. E.g. Oxygen, Iron. There are three types of elements: Metals, non-metals and metalloids.
A compound is a substance composed of two or more elements which chemically combine in a fixed proportion.
The constituents of a compound can only be separated by chemical methods.
The properties of a compound are different from the properties of its constituents.
The composition of a compound is same throughout. The same goes from the colour and texture.
E.g. Water, Copper sulphate
CHAPTER 1 MATTER IN OUR SURROUNDINGS
Matter is made up of particles which are so small that they cannot be seen by the naked eye.
CHARACTERISTICS OF PARTICLES OF MATTER
STATES OF MATTER
There are three different states of matter: solid, liquid and gas.
EFFECT OF TEMPERATURE
When the temperature of solids increases, the kinetic energy of the particles increases. Due to this increase in kinetic energy, the particles start vibrating faster. Once the energy supplied overcomes the force of attraction between the particles, they start moving freely. This is when the solid starts converting into liquid. On further heating the liquid then converts into gas.
Latent heat of vaporization is the heat energy required to change 1 kg of liquid into gas atmospheric pressure at the boiling point without changing its temperature.
Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point without any change in the temperature.
CHANGE IN STATES
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