Journal #17 What is matter? Can it be created? Or destroyed? When wood is burned, what happens to the wood? Does it disappear?

Today’s Learning Goal: Today, we will define the law of conservation of mass

Chemistry Chemistry is the study of matter and the changes it undergoes. They type of matter that is changing and what types of changes it undergoes determines the field of chemistry that is being studied

Matter Matter is defined as anything that has mass and takes up space Atoms of an element Molecules of a compound Mixture of elements

Classification of Matter The composition of a pure substance is the same throughout and does not vary sample to sample. It can be an element or a compound. Mixtures contain more than one substance and vary in composition and properties from sample to sample.

Foundations of Atomic Theory Elements found on the periodic table combine to form compounds that have different physical and chemical properties than those of the elements that form them. The transformation of a substance or substances into one or more new substances is known as a chemical reaction. Reactants  Products

The Law of Conservation of Mass The law of conservation of mass states that mass is neither created nor destroyed during ordinary chemical reactions or physical changes. A pure chemical compounds is composed of a fixed proportion of elements. Example: sodium chloride always consists of 39.34% sodium and 60.66% chlorine.

Dalton’s Postulates To explain the law of conservation of mass, a Chemist, John Dalton, reasoned that elements were composed of atoms and that only whole numbers of atoms can combine to form compounds. Dalton concluded his atomic theory: Matter is composed of atoms, which are indivisible. Each compound consists of a set ratio of atoms Atoms of the same element are identical Atoms of different elements are different Atoms are not changed, created, or destroyed in a reaction, they are simply rearranged.

Law of Conservation of Mass Dalton knew that chemical reactions occur by rearrangement of atoms. The masses of chemicals before and after a reaction remained the same, so the number of atoms before and after a reaction had to be the same as well.

Daltons Postulates Dalton had the right idea with his postulates but he was not completely correct. He was limited by the equipment he had to observe reactions Today we know that there are some forms of reactions in which the mass does change, and atoms are changed form one type of atom to another..called nuclear reactions Atoms can be broken down into smaller bits.

Let’s Review What we’ve Learned: Which one of the following is not one of the postulates of Dalton’s atomic theory? A.Atoms are made of protons, neutrons and electrons B. All atoms of a given element are identical C. Atoms are neither created nor destroyed in chemical reactions D. Compounds are formed when atoms of more than one element combine Answer: A

Law of Conservation of Mass Lab Groups Materials Safety Goggles Clean up