Elements, Compounds, and Mixtures,

Mixtures, elements, compounds 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? Because one kind of substance can exist in more than one phase – such as H20. And matter changes phases rather easily.

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

So how do scientist’s classify? Scientists ask themselves these questions? − Is the matter uniform throughout? − Can it be separated by physical means? − Can it be separated by chemical means?

Classifying Matter Matter Pure SubstancesMixtures ElementsCompounds HomogeneousHeterogeneous Fe, OH 2 O, CO 2 milk, tea Rocky Road ice cream, muddy water

What is a Pure Substance? A pure substance is a classification of matter that includes both elements and compounds Pure substances CANNOT be separated by physical means

Elements We have already studied elements − An element is made of one kind of atom − Found on the periodic table Elements are the simplest pure substance. Elements are the simplest pure substance. An element can not be changed into a simpler substance by heating or any chemical process. An element can not be changed into a simpler substance by heating or any chemical process.

What Is A Compound? A compound is a PURE substance that is created by 2 or more elements chemically reacting and joining together − Ex: NaCl, H 2 O, CO 2, NH 3, NaHCO 3, and C 6 H 12 O 6 Notice that elements combine in many ways to make compounds − Ex: H 2 O, H 2 O 2, CO, and CO 2

Common Compounds Carbon Dioxide

Why Do Compounds Form? Compounds form to allow elements to become more stable − Na is flammable when it comes in contact with H 2 O, and Cl 2 is a toxic gas − NaCl is a very stable compound that is neither flammable nor toxic (in normal quantities) − THIS IS WHAT MAKES THE PROPERTIES OF A COMPOUND DIFFERENT FROM THE PROPERTIES OF ITS ELEMENTS!

How Do Compounds Form? Compounds form between the valence electrons of 2 or more elements THE OCTET RULE: an element is most stable with 8 valence electrons − Elements will join chemically to get 8 valence electrons Ex: CO 2 : oxygen has 6 valence electrons and carbon has 4 If the carbon shares 2 with each oxygen, everyone will have 8 valence electrons!

What Do Compounds Have To Do With My Life? Compounds are the substances that make up ALL living and non-living things Examples: Where would you be without: − H 2 O—water − NaCl—table salt − C 3 H 8 O—rubbing alcohol − C 55 H 98 O 6 —an example of an unsaturated fat

What Is A Mixture? A mixture is the PHYSICAL combination of 2 or more substances It is important to understand that a mixture is not chemically combined so they keep their original properties Mixtures can be separated by physical means such as filtration, a magnet, density or evaporation Mixtures can be divided into 2 groups − Homogenous mixtures − Heterogeneous mixtures

Classifying Matter Matter Pure SubstancesMixtures ElementsCompounds HomogeneousHeterogeneous Fe, OH 2 O, CO 2 milk, tea Rocky Road ice cream, muddy water

How Do Mixtures Form ? Mixtures form by physically “mixing” 2 or more substances together Remember no chemical change is occurring, so each part of the mixture keeps its original properties

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

Examples of heterogeneous mixtures Sand and pebbles Oil and water Chex mix

Granite is a heterogeneous mixture.

Is it the same throughout? If the answer is YES, it is a HOMOGENEOUS MIXTURE Homogeneous mixtures are commonly called solutions. − Solution = Solute + Solvent Solute: “stuff” being dissolved Solvent: “stuff” doing the dissolving − Ex: Salt water: Salt=solute, Water=solvent

Examples of homogeneous mixtures

How Are Mixtures Important To My Life ? We encounter mixtures everywhere in our lives Where would you be without: − Ice cream − Kool-aid − Shampoo − Soup − Milk − Orange juice