Chemistry Form 4 A+ Notes

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    SEPT 2013

    PREPARED BY:

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    CHAPTER 2: STRUCTURE OF THE ATOM

    2.1 MATTER

    1.

    Matter : Any substance or material that occupies space and has mass. Exists as a solid, liquid or gas (3 states of matter). Made up of particles. 3 kinds of particlesatoms, molecules, ions Can be divided into elements and compound.Particles Description

    Atoms Smallest particles of an element that retain the chemicalproperties of the element.

    Examples : Sodium atom (Na)Zinc atom (Zn)

    Helium atom (He)

    Molecules Particles composed of two or more atoms. Can be with the same or different atoms Examples : Same atomsOxygen gas (O2)

    Different atomsAmmonia (NH3)

    Ions Charged particlespositive or negative Positive charged ion (Cation)Zinc ion (Zn2+)Negative charged ion (Anion)Chloride ion(Cl-)

    Matter Descriptions

    Elements Particles made up of the same atoms only. Can be in the form of atom or molecules. Cannot be split into two or more simpler substance by

    chemical means.

    Examples:- Metallic Copper(Cu), Iron(Fe), Gold(Au)- Non-metallic Oxygen(O2), Sulphur(S8)

    Compounds Particles made up of two or more elements. Can be molecules or ions. Examples:

    - MoleculesWater (H2O)Sulphur trioxide (SO3)

    Tetrachloromethane (CCl4)- Ions Sodium chloride (Na+, Cl-)

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    Iron(III) oxide (Fe3+

    , O2-

    )

    Calcium chloride (Ca2+

    , Cl-)

    2.

    Changes in states of matter Matter can change its state. Reversible changes. Exists in 3 states, solid, liquid and gas.

    During the changes, the following do not change:- Mass of particles

    - Size of particles

    - Type of particles

    Velocity of the particle increases when- Temperature increases- Kinetic energy increases

    Melting pointBoiling point

    SOLID LIQUID GAS

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    Sublimation can only happen to :- Ammonium chloride (NH4Cl)

    - Solid carbon dioxide / Dry ice (CO2)

    - Iodine (I2)

    Differences between solid, liquid and gas (Kinetic Theory Of Matter):(Essay)

    States of matter Solid Liquid Gas

    Arrangement of

    particlescompact, orderly

    manner

    Loosely packed,

    disorderly manner

    very far apart,

    random motion

    Particles motionVibrate, rotate in

    a fixed position

    Move freely Move freely and

    randomly

    Particles Kinetic

    energy

    Very low Moderate High

    Shape Fixed Not fixed (follow

    the shape of

    container)

    Not fixed (follow

    the shape of

    container)

    Volume Fixed Fixed Not fixed

    Rate of diffusion Low Average High

    Attractive forcesbetween particles

    Very strong Medium Very weak

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    3. Experiment (PeKa)a. Heating curve of naphthalene/acetamide Diagram:

    Graph:

    AB: Solid DE: Liquid + Gas

    BC: Solid + Liquid EF: Gas

    CD: Liquid

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    Explanation:AB: When the solid is heated, heat energy is absorbed. This causes the

    particles to gain kinetic energy and vibrate faster.

    BC: The temperature remains constant because the heat energy absorbed by

    the particles is used to overcome the forces between particles so that the

    solid can turn into a liquid. At this temperature, both solid and liquid are

    present.

    CD: The particles in liquid naphthalene absorb heat energy and move faster.

    During the heating of naphthalene:- Water bath is used (ensure uniform heating, naphthalene is flammable)

    - Naphthalene is stirred continuously (ensure an even heating)

    Water bath: For heating a substance which is less than 100C. Oil bath: For heating a substance which is more than 100C. Latent heat of fusion: heat required to convert solid to liquid without a

    change in temperature.

    b. Cooling curve of naphthalene/acetamide Diagram:

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    Graph:

    Explanation:RS: When the liquid is cooled, the particles in the liquid lose their

    kinetic energy. They move slower as the temperature decreases.

    ST: The temperature of naphthalene remains constant because the

    heat loss to the surroundings is balanced by the heat energy given off

    during freezing.

    TU: The particles in solid naphthalene release heat energy and vibrate

    slower.

    During the cooling of naphthalene: Boiling tube containing naphthalene is placed in a conical flask. (to

    minimize heat loss which may affect the accuracy of freezing point

    air trapped in conical flask is poor conductor of heat)

    Stirred by using thermometer (to ensure even cooling)

    PQ: Gas ST: Solid + Liquid

    QR: Liquid + Gas TU: Solid

    RS: Liquid

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    Super cooling

    i. Condition in which the temperature of a cooling liquid drops below thenormal freezing point.

    ii.

    Occurs when conical flask is not used in the experiment.

    2.2 ATOMIC STRUCTURES

    1. Historical development of the structure of atoma) John Dalton

    - All elements made up of small indivisible particles called atoms.

    - Atoms made up of tiny particles which cannot be created or destroyed.

    - Atoms of same elementsame mass

    - Atoms of different elementsdifferent mass

    - Atoms join together to form larger molecules or compounds (in simple

    ratio)

    - Weakness:

    Atoms are not the simplest particles bigger than proton, neutronsand electron

    Atoms can be destroyed or breakdownradioisotopes Atoms of same element have different massisotopes

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    b) J.J. Thomson

    - Plum pudding model.

    - Electron embedded in a sphere of positive charge.

    - Electron spreads randomly throughout the positive charge.

    c) Ernest Rutherford

    - All positive charge of an atom is concentrated in the nucleuscontainprotons.

    - Mass of atom is located in a small area (nucleus).

    - Number of protons = number of electron

    d)Neils Bohr

    - Electrons of atom are arranged and move around the nucleus in orbital

    called electron shells.

    - Nucleus contains protons.- The orbital has various radius form the nucleus.

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    e) Sir James Chadwick

    - Discovered neutrons which are located in the nucleus.

    - The neutral particle has the same mass as protons.

    2. Atomic Structure Made up of subatomic particles; protons, electrons and neutron. Nucleus situated at the centre of atom.

    has positive charge, protons. Neutrons may also present.

    Electrically neutral. (Number of proton = Number of electrons) Have electrons which move around the nucleus in its shells.

    Mass of proton = mass of neutron Nucleus contributes a lot of mass in an atom.

    Subatomicparticles

    Symbol Relative atomicmass (RAM)

    Charge

    Proton p 1 +

    Neutron n 1 neutral

    Electron e

    3. Electron Configuration Maximum number for each shell: First shell : 2 electrons Second shell : 8 electrons Third shell : 8 electrons Forth shell : 2 electrons

    Valence electron = electrons found in the outermost shell of an atom.

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    4. Atomic number & Mass number Atomic number = proton number Nucleon number = proton number + number of neutrons Mass number = Nucleon number

    2.3 KINETIC THEORY OF MATTER

    1. According to the Kinetic Theory Of Matter, Matter consists of tiny and discrete particles. Particles always move randomly. There are forces of attraction between the particles.

    Particles gain kinetic energy and move faster when heated. Particles lose kinetic energy and move slower when cooled. Can be proven by using 2 experiments: Diffusion and Brownian

    movement.

    2. Diffusion Occurs when particles of a substance move in between the particles of

    another substance.

    Random movement of particles from a high concentration region to alower concentration region.

    Happens in three states of matter; solid, liquid and gas. Occurs most rapidly in gases, followed by liquid and solid. Particles diffuse from one medium to another. Rate of diffusion increases with the temperature. Rate of diffusion decreases when the mass of matter increases. Diffusion in gases:

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    Diffusion of liquid:

    (Blue)

    Diffusion of solid:

    3. Brownian movement

    Random movement that is shown when colliding with other particle. Can only be observed under a light microscope. Supports the Kinetic Theory Of Matter.

    Jelly

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    2.4 ISOTOPES

    1. Atoms of same element with the same number of protons but differentnumber of neutrons.

    IsotopesUses

    Carbon-14 determination of age of carbon-containing artifacts as a biological tracer, for example, in studies of

    photosynthesis

    Oxygen-18 biological tracer, for example, in studies of photosynthesisSodium-24 Detect location of leaks in water pipes,

    studies of body electrolytesMagnesium-

    27 location of leaks in water pipes

    Cobalt-60 cancer treatment as tumour cells tend to be moresusceptible to radiation than other cells

    Krypton-81 lung ventilation studies

    Technetium-