Bell Work How many steps are in the scientific method? What does the atom look like? (draw a picture) What are the parts of an atom? What is the atom mostly made of?

Introduction to Chemistry The atom

Parts of an Atom The atom has two parts we talk about 1.The nucleus 2.The electron cloud

3 Major Laws In the 1700’s scientists were using improved balances and other devises that led to a better understanding of elements This also led to three laws – Law of conservation of mass – Law of definite proportions – Law of multiple proportions –

Law of conservation of mass What is a scientific law? – A law has been tested repeatedly over many years and still stands to be true What is mass? – Mass is anything that takes up space. Is mass the same everywhere? Yes

Law of Conservation of Mass What does this state? – Mass is neither created nor destroyed during chemical reactions or physical changes – This was followed shortly by another law.

Law of Definite Proportions This law state that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound In short a compound is always going to contain the same elements in the same proportion (Carbon Dioxide is always going to contain one carbon atom and two oxygen atoms)

Law of Multiple Proportions This law states if two or more different compounds are composed of the same two elements then the ratio of the mases of the second element combined with a certain mass of the first element is always a ratio of small whole numbers In short if two elements make more than one compound the two compounds proportions will be different

John Dalton John Dalton was an English school teacher In 1808 he purposed an explanation for the 3 major laws He reasoned that elements were composed of atoms and only whole atoms can combine to form compounds

Dalton’s Atomic Theory Daltons Atomic Theory can be summed up in 5 simple rules: 1.All matter is composed of extremely small particles called atoms 2.Atoms of the same element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties 3.Atoms cannot be subdivided, created, or destroyed 4.Atoms of different elements combine in simple whole-number ratios to form chemical compounds 5.In chemical reactions, atoms are combined, separated, or rearranged

Problems and Modifications Through experimentation we have come to believe that there were some problems with Dalton’s Atomic Theory 1.We know now that atoms can be divided in to smaller particles 2.Some elements differ slightly even though they are the same element – However number 1 and the second half of number 2 are unchanged