Grade 9 AY Chemistry

(F) Who discovered electrons?

J.J Thomson

(F) Who discovered protons?

E. Goldstein

(D) Canal Rays

Positevly charged radiation in gas discharges.

(F) Mass of proton is considered ______

1 unit

(F) Mass of proton is ___________ of electrons

2000 times

(F) What is charge of electron and proton

-1 and +1

(SA) Postulates of Thomson’s model of an Atom

1. An atom consists of a positively charged sphere with electrons embedded in it.

2. Both protons and electrons are equal in magnitude meaning that the atom is electrically neutral

(SA) Explain the process of the Gold Foil Experiment

1. He selected gold foil as it is maleable and can be thinned down to around 1000 atoms.

2. alpha particles are double charged helium particles . They have a mass of 4u and are fast and have high energy

3. It was expected that alpha particles are deflected by the sub atomic particles

(SA) Results of the Gold Foil Experiment

1. Most of the alpha particles passed through the foil.

2. Some of them were deflected by the alpha particles by small angles

3. One of every 1200 particles rebounded completely

(SA) Conclusions from Gold foil experiments

1. Most of the space inside the atom is empty as most of the alpha particles pass through.

2. Very few particles were deflected from their path meaning that protons occupy very little space

3. Only 1 in 1200 completely rebounded meaning that the positve mass of the atom is concentrated to a small volume.

(SA) Postulates of Rutherfords Model

1. There is a positively charged centre called nucleus where most of the mass of atom resides.

2. Electrons revolve around the atoms in circular paths

3. Size of the nucleus is small compared to the atom

(SA) What are the drawbacks of Rutherfords model of the atom

Any particle ina cicular orbit would undergo acceleration , hence causing the charged particle to radiate energy. Thus the revolving electron would lose energy and fall into nucleus causing the atom to collapse.

(D) Energy Levels

Orbits or shells in bohr’s model is called energy levels

(SA) Write a short note on neutrons.

J. Chadwick discovered the neutron. It has an equal mass of that of a proton and have no charge. It is present in the nucleus of all atoms.

(SA) How are electrons filled into orbits?

1. The maximum capacity of an orbital is 2n²

2. The maximum number of electrons in the outermost orbit is 8

3. Electrons are not filled in a shell unless it’s inner shells are filled , ie they are filled in a step wise manner.

(F) Who discovered how electrons are filled into orbitals.

Bohr and Bury

(D) Valency

The combining capacity of an atom or the amount of electrons gained or lost to achieve a noble gas configuration.

(D) Isotopes

Elements which have the same atomic number but have different mass numbers

(D) Isobars

Elements that have same mass number and different atomic numbers

(SA) Applications of Isotopes

1. Isotopes of uranium is used for nuclear reactions

2. Isotopes of cobalt is used for treatment of cancer

3. Isotopes of iodine is used for treatment of goitre

(D) Pure Substance

A substance that consists of ony a single type of consituent particle.

(D) Element

An elemnt is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

(SA) Types of Elements

1. Metals - a metal is an element that is malleahle , ductile sonorous , ocnducts electricity

2. Non Metals - not malleable , ductile , conduct electricity

3. Metalloids - intermediate properties between those of metals and non metals

(D) Compounds

A substance that is composed of two or more elements chemically combined with each other in a fixed proportion

(D) Mixture

Mixtures are consitutued by more than one kind of substnace

(D) Homogenous Mixture

A mixture in which the constituents are uniformly distrubted throught the mixture without any clear boundaries

(D) Heterogenous Mixture

A mixture that does not have a uniform composition and has visible boundaries of sepration between them

(LA) Differentiate between compounds and mixture

Compound

1. Elements are in definite ratio

2. Elements chemically combine to form a compound

3. Constituents loose their properties

4. Considerable energy is needed

5. Always homogenous

Mixture

1. Components mix in any ratio

2. Chemical reaction doe snot take place

3. They retain their properties

4. Energy is not required

5. Can be homogenous or heterogenous

(D) Solution

A homogenous mixture of two or more substances is called solution

(D) Solvent

The component of solution that dissolves the other componenet in it

(D) Solute

THe componenet of the solution that is dissolved in the solvent is called solute

(F) Example of solid solution

Alloy

(SA) Propoerties of a solution

1. Homogenous Mixture

2. Particles are smaller than 1 nanometer

3. They do not scatter light

4. Stable solution

(D) Suspension

A suspension is a heterogenous mixture in which the solute particles do not dissolve but remain suspended throughout.

(SA) Properties of Suspension

1. Heterogenous mixture

2. Particles are large in size than 1000 nanometer

3. It can scatter a beam of light

4. It is an unstable solution

(D) Colloid

A colloid is a heterogenous mixture but appears to be homogenous as particles are uniformly spread throughout the solution.

(SA) Properties of Colloid

1. Heterogenous Mixture

2. Size of particle is small around 1 to 100 nanometer

3. Stable solution

4. Cannot be seprated by filtration but by centrifugation

(D) Tyndall effect

The scattering of light by colloidal particles is known as the tyndall effect.

(SA) State the laws of Chemical Combination

Law of Conservation of Mass

Matter can neither be created nor destroyed during a chemical reaction. Ie the total mass of the products and reactants remain unchanged

Law of Constant / Definite Proportions

In a chemical substanace the elements are always present in definite proportions by mass

(LA) Postulates of Dalton’s Atomic Theory

1. Every matter is made up of a very small particle of atoms

2. Atoms are idnivisible particles which can neither be created nor destroyed in a chemical reaction

3. Atoms of a given element are identical in mass as well as chemical properties

4. Atoms of different elements have different mass and cheical properties

5. Atoms combine in the ratio of small whole numbers to form compounds

6. The relative number and kinds of atoms are constant in a given compound

(F) Which compounds do not combine in whole number ratios

Organic molecules like sugars

(D) Relative Atomic Mass

The average mass of the atom compared to 1/12th mass of a carbon 12 atom.

(D) Atomic Mass Unit

THe mass unit equal to exactly 1/12th of the mass of a carbon atom

(D) Atomicity

The number of atoms present in a molecule

(SA) Classificatiion of atoms based on atomicity

1. Monoatomic

2. Diatomic

3. Triatomic

4. Tetra Atomic

5. Polyatomic

(D) Molecule

Smallest particle of element or compound which is capable of independent existance and shows alll the properties of that substancce is called a molecule

(D) Molecular Mass

THe sum of atomic masses of all the atoms in a molecule of the susbtance

(D) Formula unit mass

IT is the sum of all the atomic masses of all atoms present in a formula unit of the compound

(D) Diffusion

The process in which molecules of substance move from area of higher concentration to an area of lower concentration.

(SA) Physical Nature of matter

1. Every matter is made up certain particles which differ in shape , size and nature

2. The particles of matter are very small

(LA) Charecterisitics of Particles of Matter

1. Particles of matter have space between them

2. Particles of matter are in a state of constant movement , ie they posses kinetic energy

3. The particles of matter have a tendendcy to diffuse

4. Particles of matter attract each other

(D) Fusion / Melting

The process of conversion of a matter from its solid state to it’s liquid state at specific conditions of temperature and pressure

(D) Melting Point

The defenite temperature point at specific temeprature and pressure the solid starts melting

(D) Boiling

The process of conversion of matter from its liquid state to its gaseous state under specific conditions of temeperature and pressure

(D) Boiling Point

THe temeprature at which a liquid starts to boil under atmospheric pressure is known as boiling point

(D) Sublimation

The process of change of solid state directly into gaseous state without passing through the liquid state upon heating is known as sublimation

(F) Examples of substances that undergo deposition

Naphthalene , camhor , iodine , ammonium chloride

Vapourisation

The proess of converting atter from its liquid state to gaseous state at specific conditions of temeperature and pressure is called vapourisation.

(SA) Difference between gas and vapour

Substance is said to be gas when its boiling point is below room temeprature ,when a substance takes on the gaseous form by aquiring energy it is known as vapour.

(D) Latent heat

The heat energt which has to given to change the sate of the substance is called latent heat

(D) Latent heat of fusion

The amount of heat energy required to change 1kg of a solid into liquid at atmospheric pressure and at its melting point is known as heat of fusion

(D) Latent heat of vapourisation

The amount of heat energy requrd to conver 1kg of gas into liquid at its boiling point without any rise in temeprature at atmospheric pressure is known as latent heat of fusion

(SA) Name the factors affecting evaporation

1. Surface Area

2. Temperature

3. Humidity

4. Wind Speed