structure of atom
DESCRIPTION
chemistry form 4TRANSCRIPT
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
Atomic structure of an atomAtoms are made of three different types of subatomic
particles called protons, neutrons and electronsProtons and neutrons are found in the nucleus and
they are known as nucleonsNucleus is positively charged because the protons
are positively charged and the neutrons are electrically neutral
Electrons rotate around the nucleus in a certain orbit called shells, just like planets rotate around the sun
SUBATOMIC PARTICLES
++
proton
neutronshell
electron
{nucleon
THE PROPERTIES OF SUBATOMIC PARTICLESSubatomic particles
Proton Neutron Electron
Symbol p n e¯
Relative electric charge
+1 0 -1
Relative mass
1 1 _1__
1840
An atom is neutral when it has the same number of protons and electrons
PROTON NUMBERThe number of protons in an atom of an
element
Proton number = number of protons
NUCLEON NUMBERThe sum of protons and neutrons in an
atom element
Nucleon number = number of protons + number of neutrons
The number of protons, electrons and neutrons in a particular atom are given in the Periodic Table by the nucleon number and proton number
A : proton numberZ :nucleon number
X: symbol of an element
The number of protons, electrons and neutrons can be determined from the nucleon number and proton number
A
X Z
Example: (a) Aluminium
The symbol of the element above shows that it is aluminium
Nucleon number = 27Proton number = 13Number of neutron = Aluminium atom has 13 protons, 13 electrons and
14 neutrons
27
Al13
27 – 13= 14
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: H1 H2 H3 , P31 P32
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
Agriculture
-radiation from radioisotopes is used to sterilise pests such as insects that destroy crops.
-Fosforus 32 use as fertiliser.Industry
-Gamma radiation is used to detect whether canned food or bottled drink is completely or partially filled