Journal #17What 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

Introduction to Atomic Structure

ChemistryChemistry 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

MatterMatter is defined as anything that

has mass and takes up spaceAtoms of an elementMolecules of a compoundMixture of elements

Classification of MatterThe 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 MassThe 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 PostulatesTo 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 atomsAtoms of the same element are identicalAtoms of different elements are differentAtoms are not changed, created, or destroyed in a

reaction, they are simply rearranged.

Law of Conservation of MassDalton 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 PostulatesDalton had the right idea with his postulates

but he was not completely correct. He was limited by the equipment he had to

observe reactionsToday 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 identicalC. 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 LabGroupsMaterialsSafety GogglesClean up