A Matter of Fact Mixtures Elements and Compounds

A Matter of Fact Mixtures, Elements and Compounds

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Mixtures, elements, compounds n n n Scientists like to classify things. One way that scientists classify matter is by its composition. Ultimately, all matter can be classified as mixtures, elements and compounds.

Why isn’t it a good idea to classify matter by its phases? n Because one kind of substance can exist in more than one phase – such as H 20. And matter changes phases rather easily.

Why isn’t matter classified according to its physical characteristics, such as color? n Scientists wouldn’t find it very useful to group gold, sunflowers, and the sun together.

Scientists ask themselves these three questions? n Is the matter uniform throughout? n Can it be separated by physical means? n Can it be separated by chemical means?

By asking these questions scientists can classify matter into: n n n Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. n Solutions – a special kind of mixture where one substance dissolves in another. Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means. Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.

Types of Mixtures n Heterogeneous n Homogeneous Solutions Suspension Emulsion Colloids

Is it uniform throughout? n If the answer is no, the matter is a heterogeneous mixture. n Considered the “least mixed. ” n Does not appear to be the same throughout. n Particles are large enough to be seen and to be separated from the mixture.

Examples of heterogeneous mixtures n Sand pebbles n Oil and water n Powdered iron and powdered sulfur

Granite is a heterogeneous mixture.

Is it uniform throughout? n If the answer is yes, the matter is homogeneous (looks the same throughout). n That leads us to another question.

Can it be separated by physical means? n If the answer is yes, the matter is a homogeneous mixture or solution.

Homogeneous Mixtures n A mixture that appears to be the same throughout. n It is “well mixed. ” n The particles that make up the mixture are very small and not easily recognizable.

Examples of homogeneous mixtures Milk, toothpaste, and mayonnaise are homogeneous mixtures. They are also colloids.

Solutions n A solution is a type of homogeneous mixture formed when one substance dissolves in another. n It is the best mixed of all mixtures. n A solution always has a substance that is dissolved and a substance that does the dissolving. n The substance that is dissolved is the solute and the substance that does the dissolving is the solvent.

Ocean water is a solution

The universal solvent: Water

Water as a solvent n Many liquid solutions contain water as the solvent. n Ocean water is basically a water solution that contains many salts. n Body fluids are also water solutions.

Air is a solution of oxygen and other gases dissolved in nitrogen

Alloys Stainless steel is a mixture of iron and chromium. Brass is an alloy of copper and zinc.

Types of solutions Solute Solvent Example Gas Gas Liquid Solid Liquid Air (oxygen in nitrogen) Soda water (carbon dioxide in water) Ocean water (salt in water) Solid Gold jewelry (copper in gold) *Metals dissolved in metals are called alloys.

In a colloid, the particles are mixed together but not dissolved. n The particles are relatively large and are kept permanently suspended. n Colloids

Colloids n n n A colloid will not separate upon standing. The particles are constantly colliding, and this allows a colloid to scatter light – thus colloids often seem cloudy. Ex. Fog, whipped cream

Suspension A mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas. n Particles are large enough to scatter or block light and are too large to stay mixed without being stirred or shaken. n Examples: Snow globe n

Suspensions n n n A suspension of liquid droplets or fine solid particles in a gas is called an aerosol. In the atmosphere these consist of fine dust and soot particles, and cloud droplets. suspension: system does not stays stable and settle Examples of Suspensions n n n n Mud or muddy water, is where soil, clay, or silt particles are suspended in water. Flour suspended in water Paint Chalk powder suspended in water. Dust particles suspended in air. Algae in water Milk of Magnesia

Emulsions n n mixture of two or more liquids in which one is present as droplets, of microscopic or ultramicroscopic size, distributed throughout the other. Emulsions are formed from the component liquids either spontaneously or, more often, by mechanical means, such as agitation

n n n Emulsions are stabilized by agents that form films at the surface of the droplets (e. g. , soap molecules) Unstable emulsions eventually separate into two liquid layers. Stable emulsions can be destroyed by inactivating or destroying the emulsifying agent Some familiar emulsions are milk (a dispersion of fat droplets in an liquid solution) and butter (a dispersion of droplets of an liquid solution in fat) Emulsions

Common ways to separate mixtures: n n n Distillation-the process of separating a mixture through evaporation and condensation. Magnet-separates a mixture using a magnet that attracts magnetic particles within the mixture from the rest of the non-magnetic mixture. Centrifuge-separates a heterogeneous mixture by spinning the liquid away from the solid

Can matter be separated by physical means? n If the answer is no, the matter is a pure substance. n An element n Or a compound

By asking these questions scientists can classify matter into: n n n Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. n Solutions – a special kind of mixture where one substance dissolves in another. Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means. Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.

Elements n n n Elements are the simplest pure substance. n An element can not be changed into a simpler substance by heating or any chemical process. The smallest particle of an element that has the properties of that element is called an atom. n An atom is the basic building block of matter. There are more than one hundred known elements in the universe listed on the periodic table of elements. n These elements combine in such a way to create millions of compounds.

Elements n n n All elements are made of atoms. Atoms of the same element are alike. Atoms of different elements are different.

n Elements In 1813, a system of representing elements with symbols was introduced. Each symbol consists of one or two letters. n Two letters are needed for a chemical symbol when the first letter of that element’s name has already been used. n

Common Elements Aluminum Bromine Calcium Carbon Gold Helium Hydrogen Nitrogen Al Br Ca C Au He H N

By asking these questions scientists can classify matter into: n n n Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. n Solutions – a special kind of mixture where one substance dissolves in another. Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means. Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.

Compounds are also pure substances. n But compounds are made from more than one element. n Water is a compound. n Water can be broken down into simpler substances – hydrogen and oxygen. n Compounds

Mini-Quiz 1. A(n) _____ is a substance made of two or more atoms chemically combined. a. mixture b. element c. compound 2. A(n)_____combination of 2 or more substances not chemically combined. a. mixture b. element c. compound 3. A(n)_____ is a pure substance that cannot be separated or broken down into simpler substances by physical or chemical means. a. mixture b. element c. compound

4. A ______ property is a characteristic of a substance that can be observed without changing the substance into another substance. a. chemical b. physical 5. A ______ property describes matter based on its ability to change into new matter that has different properties. a. chemical b. physical 6. Burning wood is an example of which property? a. chemical b. physical 7. Tearing a piece of paper is an example of which property? a. chemical b. physical

8. For dinner, you have chicken soup. It has noodles, chicken, celery, and broth. Which term best classifies this soup? a. Pure substance b. Heterogeneous mixture c. Homogeneous mixture 9. Trail mix can be classified as what type of substance based off of its multiple ingredients? a. Pure substance b. Heterogeneous mixture c. Homogeneous mixture 10. True/False: Both elements and compounds are pure substances.