Particulate Nature of MatterMatter- anything that has mass and occupies

spaceParticle + particle = matter

Iron (Fe) from iron atom

NaCl from sodium ions and chloride ion

H2O from water molecules

Atomsan atom is the smallest particle of an element example : “O” for oxygen atom

Moleculescontains two or more atoms which are bonded together ( maybe same element or not )example : H2 and CCl4

Ions-ions are charged either positive or negative-are form in liquid or molten state-lose electron (+ ion),gain electron (- ion)example : Na+ , Mg2+ , Br-

Kinetic Theory of MatterSolids

- strong forces of attraction - particle only vibrate (fixed shape and volume)

Liquids- force of attraction weak than solid- particle can move around (follow container shape)

Gases- no attraction between particles- particle move faster and freely (zigzag)

Diffusion- example : perfume- light and small particle diffuse faster- heavy and large particle diffuse slow

The Atomic StructureDemocritus

Democritus proposed that if a piece of gold cut into smaller until cannot cut anymore, called atom.

John Dalton (1766-1844)

J.J.Thomson (1856-1940)

Ernest Rutherford (1871-1937)

Neils Bohr (1885-1962)

James Chadwick (1891-1974)

John Dalton(1766-1844)In 1808, he proposed :1.All matter is composed of atoms.2.Atoms cannot be created or destroyed.3.All the atoms of an element are identical.4.The atoms of different elements are different.5.When chemical reactions take place, atoms of

different elements join together to form compounds.

J.J.Thomson (1856-1940)1. It was the first model of the atom.2. 1897- Thomson discovered the electron

(negatively- charged).3. Thomson suggested that an atom is a

positively- charged sphere with electrons embedded in it like a raisin pudding.

Ernest Rutherford (1871-1937)1. 1914- Rutherford discovered the proton2. Rutherford model was based on the alpha

particle scattering experiment3. He proposed

1) all the positive charge of an atom is concentrated in the nucleus2) an atom consists of a positively-charged nucleus with a cloud of electrons surrounding the nucleus

Neils Bohr (1885-1962)He was a student of RutherfordHe proposed

1) electrons are arranged in orbits (electron shells) around the nucleus of the atom2) electrons in a particular path have a fixed energy.

To move from one orbit to another, an electronmust gain or lose the right amountof energy

James Chadwick (1891-1974)He proposed that the nucleus of the atom

contains proton and neutron and the nucleus is surrounded by a cloud of electrons

Proton number and nucleon numberProton number = the number of protons in an

atomAlso known atomic numberNo two different element have same proton

numberAtom are neutral. Proton number also tells us

number of electron.Nucleon number also known mass numberNucleon no. = proton no. + neutron numberHow nucleon no. and proton no. of an element is

written ?

Symbol of elementsMost symbols are taken from the English

name

Element Symbol

Hydrogen

Carbon

Nitrogen

Boron

H

C

N

B

Some symbol are made up of two letters

Some symbols are based on the Latin or Greek name

Zinc Zn

Aluminium Al

Calcium Ca

silicon Si

Silver Ag

Copper Cu

Iron Fe

Gold Au

Isotopes and their importanceAre atoms of the same element with the same

proton no. but different nucleon no. or neutron no.

Isotopes of an element have same chemical properties but different physical properties

Example of isotopesSome isotopes are stable while the rest

unstable ( radioactive isotopes)

Uses of isotopesMedicine

Cobalt-60 is a radioactive isotope of cobalt. It decays by giving out gamma radiation. In radiotherapy, maglinant cancer cells are killed by directing a beam of gamma rays towards cancer cells

Agricultureradiation from radioisotopes is used to sterilise pests such as insects that destroy crops.

IndustryGamma radiation is used to detect whether canned food or bottled drink is completely or partially filled

Electronic structure of an AtomThe electron in atom are arranged in shell around its

nucleusElectron start to fill up the shells from the inner shellsThe first shell is the shell that nearest to nucleus and

can hold just 2 electronsSecond shell can hold 8 electronsThird shell can hold 8 electronsAll of this is called the electron arrangement or

electronic configuration of the atomDraw electronic arrangement if proton number is 4,5

and 6

Valence electronsOutermost shell of an atom is called the

valence shellThis shell should have electrons before it can

be called a valence shellThe electrons in the valence shell are called

the valence electronsElements with the same number of valence

electrons have the same chemical propertiesLets see the examplesusunan elektron.swf