Download worksheet_2_G_7 - answer

Port Said International Schools
Better education for future generations
Science Department
Grade: 7
Worksheet 2
Name: ………………………………………. Date: ……………………………………………………
A) What is meant by
1- density:
The mass of 1cm3 of the matter
2- atom:
The smallest part of the matter which can’t exist freely and doesn’t show the property of
the matter
3- molecule:
The smallest particle of the matter which can exist freely and has its own matter properties
B) Give reason for the following:
1- A drop of ink spreads in water.
The drop of ink disassembled into smaller particles (molecules), these molecules are in
continuous motion
2- When adding an amount of table salt to water it disappears after a time.
Because the table salts disassembled into smaller particles (molecules), these molecules are
in continuous motion
3- It is very hard to fragmentize a piece of iron with your fingers.
Because the attraction force between the iron molecules is very strong.
4- When you leave the perfume bottle opened you smell it all over the room.
Because the perfume particles are divided into tiny particles these particles are spread and
carried through the air in the room having the perfume properties.
5- The volume of a mixture of water with alcohol is less than the sum of their volumes
before being mixed together.
Because some of alcohol molecules are distributed in the intermolecular spaces found
among water molecules.
6- An ice cube changes into liquid water after a period of time.
Because it has low melting point
7- The screwdrivers electricians use are made from steel iron & they have wooden
handles.
Because iron steel is good conductor of electricity while wood is bad conductor of
electricity
8- A piece of iron isn’t broken by hands.
Because the attraction force between the iron molecules is very strong
Port Said International Schools
Better education for future generations
Science Department
Grade: 7
Worksheet 2
Determine the number of atoms from which every molecule is formed. Illustrate if they are
similar or not:
Oxygen molecule:
2 atom(s), similar
Water molecule:
3 atom(s), different
Sodium chloride molecule:
2 atom(s), different
Ammonia molecule:
4 atom(s), different