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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