Chapter 4 matter and substance
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Transcript of Chapter 4 matter and substance
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