chapter 2 the structure of the atom
TRANSCRIPT
2.1 Matter
• Matter: Anything that occupies space and has mass
• Based on theory: Matter is made up of tiny and discrete particles. There are spaces between these particles
• Types of particle:
Atoms
Molecules
Ions
• Atom: The smallest particle of an element that can participate in a chemical reaction
• Molecule: A group of two or more atoms which are chemically bonded together
• Ion: A positively-charged or negatively-charged particle
• Diffusion: Occurs when particles of a substance move in between the particles of another substance
• Diffusion of matter occurs most rapidly in gases, slower in liquids and slowest in solids → due to the different arrangement and movement of particles
• Observe this video
The arrangement and movement of particles in solid, liquid and gas are described in the kinetic theory of matter.
The Change in The State of Matter
Sublimation
Sublimation
Condensation
Boiling / Evaporation
Melting
Freezing
When solid is heated;
• The particles in the solid gain kinetic energy and vibrate more vigorously.
• The particles vibrate faster as the temperature increases until the energy they gained is able to overcome the forces that hold them at their fixed positions.
• At this point, the solid becomes a liquid. • This process called melting. • The temperature at which this happens is called
melting point.
When liquid is heated;
• The particles in the liquid gain kinetic energy and move faster.
• The particles move faster as the temperature increases until the energy they gained is able to overcome the forces that hold them.
• At this point, the liquid becomes a gas.
• This process is called boiling.
• The temperature at which this happens is called boiling point.
When liquid is cooled;
• The particles in the liquid lose energy and move slower.
• As the temperature decreases, the particles lose more energy until they did not have enough energy to move freely.
• At this point, the liquid changes into a solid.
• This process is called freezing.
• The temperature at which this happens is called freezing point.
Definition:
• Melting point
The temperature at which a solid changes into a liquid at a particular pressure.
• Freezing point
The temperature at which a liquid changes into a solid at a particular pressure.
The heating curve
Temperature (°C)
Time (min)
Melting point
A
B C
D
solid
begin to melt
liquid
solid-liquid
The temperature remains constant because: The heat energy absorbed is used to overcome the force attraction between particles so that solid can change into liquid
Heat energy is absorbed. Particles in solid gain kinetic energy and vibrate faster
Heat energy is absorbed. Particles in liquid gain kinetic energy and move faster
The cooling curve
Temperature (°C)
Time (min)
Freezing point
E
F G
H
liquid
solid
liquid-solid
The temperature remains constant because: The heat loss to the surrounding is equal to the heat energy formed during particles attraction to form a solid
Heat energy is released. Particles in liquid lose kinetic energy and move slower
Heat energy is released. Particles in solid lose kinetic energy and vibrate slower
2.2 The Atomic Structure
Historical development of atomic models Model Structure Characteristic
Dalton’s atomic model proposed by John Dalton in 1805
The atom was imagined as a small indivisible ball similar to a very tiny ball.
Thomson’s atomic model proposed by J.J. Thomson in 1897
J.J Thomson discovered electron, a negatively-charged particle. The atom was described as a sphere of positive charge embedded with electrons.
Model Structure Characteristic
Rutherford’s atomic model proposed by Ernest Rutherford in 1911
Ernest Rutherford discovered proton, a positively-charged particle in an atom. The central region of atom has a very small positively-charged nucleus, which contains almost all the mass of the atom.
Bohr’s atomic model proposed by Neils Bohr in 1913
The electrons in an atom move in shells around the nucleus which contains protons.
Model Structure Characteristic
Chadwick’s atomic model proposed by James Chadwick in 1932
Chadwick proved the existence of neutrons, the neutral particle in the nucleus. The nucleus of the atom contains protons & neutrons, and the nucleus is surrounded by electrons.
Relative electric charge: +1 Relative mass: 1
Relative electric charge: 0 Relative mass: 1
Properties of subatomic particles
Nucleus
Proton, p
Neutron, n
Relative electric charge: -1 Relative mass: ≈ 0.0005
Electron, e
Proton number and nucleon number
Proton number:
The number of proton in its atom
** also shows the number of electrons in the atom
Nucleon number:
The total number of protons and neutrons in its atom
** also known as mass number
What is the relationship??
Nucleon number
Proton number
Number of neutrons = +
Nucleon number
Number of protons
Number of neutrons = +
OR
2.3 Isotopes and Their Importance
Isotopes:
• Atoms of the same element with same number of proton but different number of neutrons.
OR
• Atoms of the same element with same proton number but different nucleon number.
Uses of isotopes in our daily lives
In the medical field: • Cobalt-60 Used in radiotherapy for the treatment of cancer • Iodine-131 Treatment of thyroid gland In the argiculture field: • Phosphorus-32 Study the metabolism of phosphorus in plants • Gamma ray of cobalt-60 Used to destroy bacteria in food
Uses of isotopes in our daily lives
In industrial field:
• Sodium-24
Used detect leakages in pipes
In archeology field:
• Carbon-14
To estimate the age of fossils and artifacts
2.4 The Electronic Structure of an Atom
The first shell : 2 electrons
The second shell : 8 electrons
The third shell : 8 electrons
Nucleus
Example:
Chlorine atom
• Proton number of 17
• Hence, chlorine atom has 17 electrons
• Electron arrangement:
2.8.7