Matric Notes Chemistry Class 9 Chemistry Definitions

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Chemistry Definitions

Acidity

The acidity of a base is defined as the number of ionizable hydroxyl groups in its molecule.

Anode

It is an electrode through which electrons enter the external circuit.

Alpha Rays

There are positively charged particles emitted from a radioactive substance. They carry two positive charges and are called helium nuclie.

Analytical Chemistry

It is the branch of chemistry which discusses the analytical methods forgetting information about chemical compounds and chemical processes.

Atomic Number

Number of positively charged particles (protons) present in the nucleus of an atom.

Atomic Size

Average distance between the nucleus of an atom and its outermost electronic shell. Its units are nm or pm.

Arrehenius Acid

It is a chemical compound which gives proton (H+) in water.

Arrehenius Base

It is a chemical compound which gives hydroxide ion (OH-) in water.

Atomic Spectrum

Spectrum of radiations emitted by the excited atoms when they come to the normal state.

Acidic Salts

An acidic salt is obtained when hydrogen atoms present in an acid, are partially replaced by metallic atoms.

Alchemist

A scientist trying to convert cheaper metals into precious metals is called Alchemist and this branch of chemistry is called Alchemy.

Atomic Mass

The mass of an element relative to the unit mass, which is 1/12th o the mass of C-12.

Ampere

The amount of electric current which liberate one electrochemical equivalent of a substance per second during electrolysis of that substance is called ampere.

Biochemistry

It is the study of chemical compounds present in living things.

Balancing of Chemical Equations

Equating the atoms of reactants with those of products.

Beta Rays

These are electrons emitted from a radioactive substance.

Brownian Movement

The free movement of the molecules of gases and liquids is called Brownian movement.

Bronsted Acid

A compound which can donate proton.

Bronsted Base

A compound which can accept proton.

Basicity

The basicity of an acid is defined as the number, of ionizable hydrogen atoms present in its molecule.

Basic Salts

A basic salt is obtained when the hydroxyl groups present in a base are partially replaced by some other groups.

Boiling Point

A temperature at which a liquid changes into gaseous state.

Chemistry

The branch of science, which deals with the composition of matter changes in matter and the laws or principles which govern these changes.

Chemical Equation

The representation of a chemical change in terms of symbols and formulas.

Covalent Solid

A solid in which there exist a covalent bond between atoms.

Covalent Bond

It is the force of attraction that arises between two atoms due to mutual sharing of an electron pair.

Co-Ordinate Covalent Bond

When the shared pair of electrons is provided by one of the bonded atoms, a coordinate covalent bond is formed.

Cohesive Forces

The forces of attraction present between the particles of solid, liquid and a gas.

Cathode Rays

Rays emitted from cathode in the discharge tube.

Colloidal Solution

A solution in which solute particles are bigger than those present in a true solution and which cannot be filtered.

Conductor

A substance which allows electric current to pass through it.

Cathode

It is an electrode through which electrons leave the external circuit.

Concentration of a Solution

The amount of a solute which has been dissolved in a particular amount of a solvent.

Concentrated Solution

A solution, which contains an excess amount of a solute as compared to that of a solvent.

Cell

The vessel containing reacting substances in which transfer of electrons takes place is called cell.

Coulomb

It is unit of electric current. When one ampere electric current is passed for one second the quantity of electric current is one coulomb.

Discharge Tube

A glass tube containing a gas at a very low pressure and provided with electrodes to study the passage of electricity through the gas.

Dipole-Dipole Forces

The forces of attraction which originate due to the difference in electro negativities of the bonded atoms in polar molecules.

Diffusion

The movement of molecules from a higher concentration to a Lower concentration is called Diffusion.

Dilute Solution

A solution, which contains a small amount of a solute as compared to that of a solvent.

Double Salts

When two typical salts are crystallized together a double salt is formed. The physical properties of the crystals of double salt are different from those of the component salts.

Doberiner’s Law of Triads

Dobereiner arranged similar elements in sets of three, called Triads. Atomic mass of the middle atom of a triad was equal to the average of the atomic masses of first and third members.

Degree of Ionization

It is the extent to which an electrolyte ionizes in water.

Experiment

An experiment is an activity performed under suitable conditions with specially designed instruments to get the required information.

Empirical Formula

The formula of a compound which shows the minimum ratio present between the atoms.

Electron Affinity

The amount of energy given out when an electron is absorbed in the outermost electronic shell of all isolated gaseous atom. Its units are KJ/mol.

Electro-Negativity

It is the power of an atom to attract the shared pair of electrons.

Evaporation

The continuous escape of the molecules of a liquid from its surface.

Elastic Collision

When gas molecule collides with each other their total energy does not decrease or increase. This type of collision is called an elastic collision.

Electrolytic-Cell

In a non-spontaneous oxidation-reduction reaction takes place with the help of electrical energy.

Electro-Chemistry

It is that branch of chemistry in which chemical energy is converted into electrical energy or electrical energy is converted into chemical energy.

Electrolytes

When electricity is passed through an ionic compound which is either in the fused state or in the form of aqueous solution, it is decomposed into its constituents. The ionic compound is called an electrolyte.

Electrolysis

The passage of electricity through an electrolyte is called electrolysis.

Electrochemical Series

A list of ions in which they are arranged in the order of their ability to get discharged.

Electroplating

The process of depositing a metal on another metal with the help of electricity.

Exothermic Reaction

Those chemical reactions during which heat is evolved.

Endothermic Reactions

Those chemical reactions in which heat energy is absorbed.

Enthalpy of Reaction

Heat of reaction which takes place at constant pressure.

Formula Mass

Formula mass is the mass of compound relative to the unit mass which is 1/12th of the mass of C-12.

Farad

It is the unit of charge 1 farad = 96500 coulomb.

Fusion

When a solid change into liquid this phenomena is called Fusion.

Heat of Neutralization

The heat given out during a neutralization reaction is called heat of neutralization.

Heat of Reaction

Heat evolved or absorbed during a chemical reaction which takes place at pressure.

Hypothesis

In the light of experiments, the scientists try to explain observations and facts. This tentative explanation is called hypothesis. It is quite possible that after sometime, on the basis of new experiments this hypothesis may be rejected.

Hydrogen Bonding

When a hydrogen atom is attached to any one of fluorine, oxygen and nitrogen atoms, there appears strong dipole forces which are called hydrogen bonding.

Hydrated Ions

Ions of a solute surrounded by water molecules are called hydrated ions.

Ionization

An electrolyte splits up into charged particles upon heating or in its aqueous solution. This process is called Ionization.

Ionic Theory

A theory which explains the process of electrolysis.

Intermolecular Forces

The forces of attraction present between the molecules of a compound.

Ionization Energy

The minimum amount of energy required to remove an electron from the outermost electronic shell of an isolated gaseous atom. Its unit is KJ/mol.

Ionic Bond

A bond formed due to the electrostatic force of attraction between oppositely charged ions.

Ionic Solid

A solid which is made up of ions of opposite charges.

Isotope

Atoms of an element having the same atomic number but different mass number.

Inorganic Chemistry

The study of all elements and their compounds except carbon is called inorganic chemistry.

Industrial Chemistry

The application of chemical knowledge in technology and industry and the preparation of industrial products are called industrial chemistry.

Inference

To deduce results after coordinating the observed facts with integrated scientific knowledge is called inference.

Kinetic Theory

The theory which explains the composition and properties of all the three states of matter.

Lewis Acid

A substance which can accept an electron pair.

Law

A theory when repeatedly gives the same results after experimentation and offers correct explanation of scientific facts it then becomes a law or principle.

Law of Conservation of Mass

Total mass of reactants is equal to that of products during a chemical reaction.

Law of Definite

A compound always contains elements combined together in a fixed ratio by mass.

Law of Multiple Proportions

When two elements combine together to give more then one compounds, the different masses of an element, which combine with the fixed mass of the other element, have a simple ratio between them.

Law of Reciprocal Proportions

When two or more elements A and B combine separately with the fixed mass of the third element E the ratio in which they do so may be the same or some simple multiple of the ratio in which these two elements (A and B) combine with each other.

Molar Solution

A solution in which one mole of a solute has been dissolved in one dm3 of solution. It is represented as M.

Metallic Bond

When positively charged metal ions are held together by freely moving electrons, the bond formed is called a metallic bond.

Molecular Solid

A solid which has Vander Waal’s forces present between its molecules.

Melting Point

A temperature at which a solid changes into a liquid.

Mass Number

The total number of protons and neutrons present in the nucleus of an atom.

Mendeleev’s Periodic Law

Properties of elements are a periodic function of their atomic masses.

Modern Periodic Law

Properties of elements are a periodic function of their atomic numbers.

Molecular Mass

Molecular mass is the mass of an element or a compound relative to the unit mass, which is 1/12th of the mass of C-12.

Molar Mass

The mass of an element or a compound which contains Avogadro’s number particles.

Molecular Formula

The formula of an element or a compound which tells the actual number of atoms present in the molecule of that element or a compound.

Neutralization

Acids and bases react together to form salts and water and in this way they neutralize the properties of each other. This reaction is called Neutralization reaction.

Normal Salts

Salts, which neither have replaceable hydrogen atoms nor hydroxyl groups.

Non-Conductor

A substance through which electric current cannot pass.

Neutron

It is the smallest neutral particle present in the nucleus of atoms. Its mass is slightly more than that of a proton.

Nucleus

Central part of an atom where most of its mass is concentrated. Its size is very small as compared to the size of the atom.

Newland’s Law of Octaves

If elements are arranged in the increasing order of their atomic masses every 8th element repeats the properties of the 1st element.

Oxidation

A chemical reaction in which oxygen is added or hydrogen is removed or electrons are lost.

Octet Rule

When an atom has eight electrons in its outer most shell, its is said to be stable and does not combine with other atom to reduce its energy. This is called octet rule.

Organic Chemistry

The branch of chemistry in which we study the compounds of carbon.

Observation

The process of observing natural phenomena with the help of five senses and the scientific equipment.

Orbits

The circular path of an electron around the nucleus.

pH Scale

The negative log of hydrogen ion (H+) concentration present in a solution is called pH. This scale measures the concentration of hydrogen ions present in a solution.

Percentage by Mass

Volume of a solute present in 100cm3 of a solution.

Percentage by Volume

Volume of a solute present in 100 cm3 of a solution.

Physical Chemistry

The branch of chemistry, which deals with the physical properties and physical behavior of material things.

Prediction

The inference based on observed facts.

Proton

It is the smallest positively charged particle present in all kind of atoms. The mass of this particle is equal to the mass of the hydrogen nucleus (H+).

Positive Rays

Rays produced in the discharge tube, which are traveling in a direction opoposite to the cathode rays.

Reversible Reaction

Chemical reaction, which takes place both directions, forward as well as backward.

Reduction

A chemical reaction in which hydrogen is added or oxygen is removal or electrons are absorbed.

Radioactive Rays

Rays emitted from radioactive element or their compounds, which can cause fogging of the photographic plate.

Strong Acid

An acid which ionizes completely in water.

Strong Base

A base which can ionize completely in water giving excess of hydroxide ions.

Sublimation

Some solids, upon heating, change directly into vapors instead of changing into liquid.

Scientific Method

The method which helps to collect facts on the basis of observations and experiments. Theories and laws are then formulated to explain these facts.

Solute

The substance present in relatively lesser amount in a solution.

Solvent

The substance present in excessive amount in a solution.

Solvated Ions

Ions of a solute surrounded by solvent molecules in a solution are called solvated ion.

Saturated Solution

A solution, which contains the maximum amount of a solute at a particular temperature and which is unable to dissolve further amount of solute in it.

Supersaturated Solution

A solution which contains an amount of solute more than that required for the preparation of a saturated solution at a particular temperature.

Standard Solution

A solution whose concentration is known.

Solubility

The amount o solute in grams which can dissolve in 100 gm of solvent at a particular temperature to give a saturated solution.

Suspension

A mixture in which solute particles do not dissolve in solvent.

Strong Electrolytes

An electrolyte which completely ionize in water.

Transition Elements

Elements having incomplete penultimate (next inner to the outermost) electronic shell.

Theory

If a hypothesis is accepted (after discussion and experimentation) it is called a theory.

Thermo Chemistry

It is the branch of chemistry in which we study the heat changes during a chemical reaction.

Unsaturated Solution

A solution, which can dissolve further amount of a solute at a particular temperature, is called unsaturated solution.

Unified Atomic Mass Unit

Unit of a new scale, which is equal to 1/12th of the mass of C-12.

Voltaic Cell

In a cell a spontaneous oxidation-reduction reaction is used to produce electric current.

Weak Electrolyte

An electrolyte which undergoes partial ionization in water.

Weak Base

A base which ionizes partially in water.

Weak Acid

An acid which ionizes partially in water.

Water of Crystallization

The number of water molecules present in the crystals of a solid.