Mixtures – a combination of substances in which each substance retains its individual properties

Heterogeneous mixtures – mixtures that do not blend evenly throughout

Homogenous mixtures – have a constant composition (also known as solutions)

Types of solutions SystemExample Gas – gasAir is primarily a mixture of nitrogen, oxygen and argon gases Gas – liquidCarbonated beverages contain carbon dioxide gas in solution Liquid – gasMoist air contains water droplets in air Liquid – liquidVinegar contains acetic acid and water Solid – liquidSweetened powder drink contains sugar and other solid ingredients in water. Solid – solidSteel is an alloy of iron containing carbon

Separating Mixtures Filtration – a technique that uses a porous barrier to separate a solid from a liquid

Distillation – a separation technique based on the boiling points of the substances involved

Crystallization – is a separation technique that results in the formation of pure solid particles of a substance from a solution containing the dissolved substance

Chromatography – is a technique that separates the components of a mixture on the basis of the tendency of each to travel across the surface of another

Elements An element is a pure substance that cannot be separated into simpler substances Only 91 of the elements occur naturally Each element has its own chemical name and symbol

The elements are found on the Periodic Table of Elements Dmitri Mendeleev revolutionized the periodic table by setting it up into rows and columns Many scientists have contributed to the set up we use today

Compound – a combination of two or more elements that are combined chemically

When two or more elements combine to form a compound they lose their individual properties, and have a new set of properties Example: table salt is made of sodium and chlorine Sodium is a metal Chlorine is a poisonous gas Together, sodium chloride, is a white crystal substance safe to eat

Law of definite Proportions This law says that the elements that form compounds, combine in definite proportions. Regardless of amount, a compound is always composed of the same elements in the same proportions by mass

Percent by Mass Shows the ratio of the mass of each element to the total mass of the compound Percent by mass = mass of element x 100 mass of compound

Law of Multiple Proportions Different compounds are formed by a combination of the same elements H2O2 and H2O Ratio of oxygen is 2:1

Early Theories and Ideas of Atoms Democritus’s Ideas of an Atom- Matter is composed of empty space through which atoms move Atoms are solid, homogeneous, indestructible and indivisible Different types of atoms have different sizes

Democritus ideas were just ideas NOT science. He was ahead of his time in his thinking.

Dalton’s Atomic Theory- All matter is composed of small particles called atoms All atoms of a specific atom are identical, having the same mass, size and shape. Atoms of a specific element are different from those of other elements Atoms cannot be created or divided Different atoms combine to form compounds In a chemical reaction, atoms are separated, combined or rearranged

` Research continued and proved some of Dalton’s theory to be wrong Scientist accidently discovered something known as the cathode ray. The cathode ray is a tube where radiation strikes a coating that produces a light

The discovery of the cathode ray has led to the invention of the television The cathode ray tube led scientist to discover negative charged particles

JJ Thomson used the cathode ray tube to continue research on atoms He discovered that there are particles smaller then the atom, meaning atoms can divide into smaller subatomic particles. Thomson had identified the first subatomic particles: the electron

Robert Millikan determined that electrons were negative and have a mass of about 9.1 x g

JJ Thomson’s atomic theory is known as the Plum Pudding Model He described it as the negative charges are like plums embedded into a positive pudding

JJ Thomson’s Atomic Theory – Thomson knew that atoms had smaller particles that were called electrons and were negative He also knew that all matter is neutral in charge He created a model that would support these, it was called the plum pudding model A modern day name could be a chocolate chip cookie dough model.

And the research continues…. Ernest Rutherford became curious about positively charged alpha particles and how they interacted with solid matter Rutherford and a few other scientists designed an experiment to see how alpha particles would act when aimed at a thin sheet of gold foil

A ray of alpha particles was beamed at a thin piece of gold foil A zinc sulfide coated screen surrounded the gold foil produced a flash whenever an alpha particle struck it By seeing the flashes they would be able to see if the gold foil deflected the particles

Rutherford believed that the particles would just pass through the foil with little deflection However, several particles deflected back at large angles, some even right back to the source Rutherford and his scientist were amazed, he said it would be similar to firing a large artillery shell at a sheet of paper and having the shell come back and hit you

Rutherford made these conclusions from his experiment: Atoms consist of mostly empty space Tiny dense region centrally located in the atom, nucleus, that contained positive charge and all of its mass Electrons move through the empty space around the nucleus.

8 years after the Gold Foil Experiment Rutherford concluded that the positively charge nucleus contained particles called protons In 1932 James Chadwick showed that an atom contained a third subatomic particle. The neutron, located in the nucleus, is neutrally charged

Protons, neutrons and electrons are the 3 subatomic particles that make up an atom

Niels Bohr’s Atomic Theory – There is a positively charged nucleus Electrons orbit the nucleus similar to the planets in the solar system Electrons are in orbitals Each orbital has an energy associated with it

Electron Cloud Model The electron cloud model was formed based on the previous models and contributions from many scientist. Nucleus contains protons and neutrons Electrons are outside the nucleus Electron movement is described by regions with fuzzy boundaries causing a cloud.