Question

read chapter 2 introduction (pg. 29) and do pre - reading questions (pg. 29)
2.1 how do atoms differ from molecules?
2.2 give an example of each of the following: a solid, a liquid, a gas.
2.3 describe a chemical change (chemical reaction) you have witnessed outside of school. how do you know that it is a chemical change?
2.4 how would you separate a mixture of sand and water? what about salt and water?

Explanation:

Step1: Define atoms and molecules

Atoms are the basic building - blocks of matter, the smallest units of an element that retain the properties of that element. Molecules are made up of two or more atoms chemically bonded together.

Step2: Provide examples of states of matter

A solid example is a rock, which has a definite shape and volume. A liquid example is water, which has a definite volume but takes the shape of its container. A gas example is oxygen, which has no definite shape or volume and fills the entire container it is in.

Step3: Describe a chemical change

Burning wood is a chemical change. We know it is a chemical change because new substances are formed (ash, carbon - dioxide, etc.), there is a change in color and heat is released.

Step4: Explain separation methods

To separate sand and water, we can use filtration as sand is insoluble in water and will be retained by the filter paper while water passes through. To separate salt and water, we can use evaporation. Heating the salt - water mixture will cause the water to evaporate, leaving the salt behind.

Answer:

2.1 Atoms are the smallest units of an element, molecules are made of two or more atoms bonded together.
2.2 Solid: rock; Liquid: water; Gas: oxygen.
2.3 Burning wood is a chemical change. New substances are formed, color changes and heat is released.
2.4 Sand and water: filtration; Salt and water: evaporation.