Every day may not be good but there is something good in everyday. ~Unknown

Dalton Postulates Each element is composed of extremely small particles called atoms All atoms of a given element are identical; the atoms of different elements are different and have a different properties (including different masses). Atoms of an element are not changed into different types of atoms by chemical reactions; atoms are neither created nor destroyed in chemical reactions. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Atoms The basic building blocks of matter. They are the smallest particles of an element that retain the chemical identity of the element. This explains the following laws: Law of Constant Composition Law of Conservation of Mass Law of Multiple Proportions

Law of Constant Composition In a given compound the relative numbers and kinds of atoms are constant. Meaning: the quantity of atoms you starts with doesn’t change regardless of the chemical changes a compound takes. If you start with 2 hydrogens and 1 oxygen, you will still have the same number of atoms at the end of the reaction.

Law of Conservation of Mass The total mass of materials present after a chemical reaction is the same as the total mass before reaction.

Law of Multiple Proportions If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers. Example: Let’s consider elements hydrogen and oxygen. In forming water, 8.0 g of oxygen combines with 1.0 g of hydrogen. In hydrogen peroxide there are 16.0 g of oxygen per 1.0g of hydrogen. Therefore the ratio is: 2:1.

Back to atoms Atoms are the smallest particles of an element but they can be further broken down into smaller subatomic particles. As mentioned on Tuesday, atoms consist of three subatomic particles: Proton (+) positive charged Neutron (Neutral) no charge Electron (-) negative charged

Review So, an atom written has a atomic number and mass number on a periodic table. Atomic number Chemical Symbol Element Name Mass number

Science Background As mentioned on Tuesday, everything that occupies space is matter. Furthermore, everything can be put into one of two categories: Matter or Energy. Matter: the material of the universe Energy: the drive that makes things happen.

Matter Made up of 90 naturally occurring chemical elements For example, sulfur, silver, hydrogen, and iron All elements combine in various ways to form the great variety of substances that make up the universe. Earth is made up of eight elements making up 98% of the minerals. This elements are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, hydrogen, and magnesium. In living organisms 98.5% of the atoms are nitrogen, oxygen, carbon, hydrogen, phosphorus, and calcium.

What is Matter Matter is everything that takes up space. Example, book, table, you, etc. Name the three states of matter: Solid, liquid and gas.

Review Definition on states of matter Solid: A solid keeps its own shape Liquid: A liquid takes the shape of it’s container Gas: Does not have a set shape or volume

Side Note Atoms are not usually found in pure (elementary form) in nature. Elements are attached to other atoms in stable associations of molecules. This are known as compounds. For example, H2O (water) or CO2

Review When putting two or more kinds of matter are combine, the result is a Simple mixtures include: sand and water, oil and vinegar, nuts and bolts, coleslaw, rocky-road ice cream, and trail gorp (mix of nuts, dried fruit and/or candy). Mixture.

Mixing material For example, water and salt mixed. The solid salt seems to disappear in the water. This process is known as dissolving. This special mixture is a solution. In this case, the solid is a solute and the liquid is a solvent. If the solution were to be heated the water will undergo a phase change from liquid to gas, leaving salt behind.

Review Most solutions are made by mixing a solid and a liquid, but mixtures of matter in other states can also form solutions. Air is a solution made of several gases: Nitrogen, oxygen, oxygen, helium, carbon dioxide, and small amounts of many other gases.

Investigating Solutions In addition of mixing solutions, the ratio that solute and solvent can vary. This is the concentration of a solution. If the solute is high than the solvent then the solution is saturated. If the solute is lower than the solvent then the solution is diluted.

Saturated Diluted

Chemical Reaction When solid materials dissolves and seems to disappear in a liquid, this is a When two solutions are mixed, another kind of change can take place. It is a chemical reaction. A chemical reaction takes place and in order to retrieve the original materials another chemical reaction needs to take place. physical change.