Chapter 2 form 4
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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