CHAPTER 2THE STRUCTURE OF THE ATOM

Determining the physical state of a substance at a certain temperature

Example:1. Ethanol has a melting point of -117C and its boiling point is 78C. Complete the table below.

Temperature / CPhysical state-120Solid3085780

Example:1. Ethanol has a melting point of -117C and its boiling point is 78C. Complete the table below.

Temperature / CPhysical state-120Solid30Liquid85Gas78Liquid and gas0Liquid

2. The table below shows the melting points and the boiling points of four substances. Complete the table.

SubstanceMelting point / CBoiling point / CPhysical state at

0 C-50 C300 CA-100-35B-758C-6225D44280

2. The table below shows the melting points and the boiling points of four substances. Complete the table.

SubstanceMelting point / CBoiling point / CPhysical state at

0 C-50 C300 CA-100-35GasLiquidGasB-758C-6225D44280

2. The table below shows the melting points and the boiling points of four substances. Complete the table.

SubstanceMelting point / CBoiling point / CPhysical state at

0 C-50 C300 CA-100-35GasLiquidGasB-758LiquidSolidGasC-6225D44280

2. The table below shows the melting points and the boiling points of four substances. Complete the table.

SubstanceMelting point / CBoiling point / CPhysical state at

0 C-50 C300 CA-100-35GasLiquidGasB-758LiquidSolidGasC-6225LiquidSolidGasD44280

2. The table below shows the melting points and the boiling points of four substances. Complete the table.

SubstanceMelting point / CBoiling point / CPhysical state at

0 C-50 C300 CA-100-35GasLiquidGasB-758LiquidSolidGasC-6225LiquidSolidGasD44280SolidSolidGas

3. The table above shows the melting points and the boiling points of substance W, X, Y and Z. Which substance is in solid state at 100 C ?

Answer: Y

SubstanceMelting point / CBoiling point / CW-197-166X55138Y115144Z-7158

(c) The inter-conversion of the states of matterHeating a substance (from solid state liquid state gaseous state)The heating curve obtained:

B C: The temperature does not increase during heating because the heat energy absorbed is used to overcome the forces of attraction between the particles. This causes the substance to change from solid to liquid.

D E: The temperature remains unchanged during heating because the heat energy absorbed is used to overcome the forces of attraction between the particles of the liquid.

(ii) Cooling a substance (from gaseous state liquid state solid state

Q R: The temperature remains unchanged during cooling because the heat energy liberated during the formation of bonds is exactly balanced by the heat lost to the surroundings.S T: The stronger bonds formed during freezing release heat energy. The heat energy released is the same as the energy lost to the surroundings during cooling. Thus the temperature remains unchanged.

2.2 ATOMIC STRUCTUREThe historical development of atomic modelsIn 1805, John Dalton proposed his atomic theory of matter:All matter is made of atomsAtoms are indestructibleAll atoms of one element are exactly the same, but they are different from atoms of another elements.Atoms combine in a small whole numbers to form compounds

In 1897, J.J Thomson discovered electrons.

In 1911, Ernest Rutherford discovered protons.He said that the mass of an atom is concentrated in the nucleus which contains positively-charged particles.

In 1913, Neils Bohr suggested that electrons are found in shells orbiting at fixed distances from the nucleus.

In 1932, James Chadwick proved that neutrons exist.He discovered that the neutron is found in the nucleus.

Subatomic particles of an atom Tiny particles in an atom is called subatomic particles.They are protons, electrons and neutrons.

Proton number & Nucleon numberProton number, Z the number of protons in an atom of an element.Nucleon number, A the number of protons and neutrons in the nucleus of an atom.A = p + nA = Z + n n = A ZAtoms are neutral particles, so the number of protons is equal to the number of electrons.The standard representation for an atom of an element is:

Eg:

Example

Calculation involving proton number and nucleon numberExample:Element X has a proton number of 13 and the nucleon number of 27. what is the number of protons, neutrons and electrons of element X ?

p = 13

n = 27-13= 14

e = 13

An atom of element Y has 22 neutrons and 18 electrons. What is the proton number and the nucleon number of element Y?

Proton number = e= 18

Nucleon number = p + n= 18 + 22= 40