A change in state is always accompanied by either a loss or gain in HEAT

Melting

Occurs at melting point of the solid; ice is at 0ºC

The heat absorbed increase the kinetic energy causes them to vibrate vigorously

The attractive forces between them can no longer hold them in their fixed structure as in solid

Freezing

Reverse of melting Happens at freezing point at 0ºC The liquid is cooled and heat is released Kinetic energy decreased, molecule’s

motion slowed down The distance between molecules

decreased Attractive forces increased and caused

molecules to be bonded forming the solid

Condensation

Reverse of boiling When vapour(gas) is cooled, heat is

removed This reduced kinetic energy and

speed of molecules The distance between them is

reduced and attraction between molecules increase

Liquid formed

Sublimation

Occurs when a solid changes directly into its gaseous state

Happen at fixed temperature Heat is absorbed by the solid is

converted to kinetic energy and sufficient to overcome the forces of attraction and take them far apart into gaseous state

Examples: iodine, dry ice, ammonium chloride crystal

Boiling

Occurs at 100ºC Liquid is heated, the heat is

absorbed causes the kinetic energy increased

When *KE gained is sufficient to overcome the forces of attraction, the molecule escape the liquid surface and become molecule of gas

HEATING

P to Q - The substance is in a solid state. The particles

absorb heat energy and vibrate faster. The temperature of the substance increases.

Q to R- At Q(melting starts), the particles have enough

energy to break away from one another. From Q to R the substance is MELTING, and the temperature DOES NOT RISE. The energy absorbed is used to overcome the force of attraction between the particles.

R to S- At R, the substance has completely

melted. The particles are free to move. The particles move faster as more energy is absorbed and the temperature rises

COOLING

K to L- The substance is in a liquid state. As it cools, heat

energy is RELEASED. The particles LOSE kinetic energy and move close to one another

L to M- At L, the substance begins to SOLIDIFY. The

particles begin to arrange themselves in an orderly manner. At M, the substance has turned into a solid state

M to N- The substance is now in a SOLID state. It loses

heat and its temperature gradually cools to the room temperature. At N, the substance is at *RT

The structure of an atom

Made up of a central nucleus: protons+neutrons

The electrons are continuously moving around in permissible orbits

Nucleon number and proton number

Protons and neutrons in a nucleus are collectively called nucleons

Ex: irons have 26 protons and 30 protons, the sum will be 56 nucleons

Total number of nucleons is nucleon number (mass number,A) is equal to the sum of the no of neutrons(neutron number,N) and the number of protons, the proton number (also called atomic number, Z)

For a neutral atom,total no of electron is equal to the proton no.

XA

Z

Mass (nucleon number)

Atomic (proton number)

Element

Isotopes

The proton no of a nucleus determines what element it is

However, the no of neutrons can varies

Isotopes are atoms of the same element that have the same proton number but differing nucleon number