[PDF] Unit 2 – Definitions Pure substance. Element Atom. Compound

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2.1 Definitions

Pure substance

Element Atom Compound Heterogeneous

mixture

Solution suspension colloid Homogeneous

mixture

Qualitative Quantitative

Miscible Immiscible

Matter - anything that has mass is made up of matter. Pure Substance - A sample of matter (stuff) that consists of only one component material with physical and chemical properties that are the same with all matching materials.

Examples: water, wood, sand, sugar salt.

Atom- the smallest particle of an element. Matter is composed of atoms in various combinations. Atoms can be considered the building block of all matter. From: http://education.jlab.org/qa/history_01.html Around 2,500 years ago this Greek philosopher named Democritus was sitting around just thinking. He was thinking about cutting stuff up and came up with the idea that there must be a point where you could no longer cut something any smaller. He named the atom after the Greek word atomos, which means that which can't be split. The cool part is that he was right, well 90% right. We can split atoms, but if you split an atom it becomes something else. An atom is the smallest unit of a particular kind of material. For example if you cut a gold block into smaller and smaller pieces you would eventually be left with one gold atom. If you cut that atom into pieces you don't get smaller pieces of gold, you get protons, neutrons and electrons, which can be rearranged into something completely different. Democritis was mostly correct and well ahead of his time.

What does an atom look like?

This is an image of silicon

atoms arranged on a face of a crystal. It is impossible to "see" atoms this way using ordinary light. The image was made by a Scanning

Tunneling Microscope, a

device that "feels" the cloud of electrons that form the outer surface of atoms, rather as a phonograph needle feels the grooves in a record. It had long been suspected that crystals are made of atoms lined up in neat arrays. But at the start of the 20th century there was no way to actually see them. Some scientists thought the "atom" in physics theories might be merely a sort of abstract device useful for computations. Einstein's paper gave one of the first convincing proofs that atoms do exist as real objects. From: http://www.aip.org/history/einstein/atoms.htm Element- a substance whose atoms are all the same. This means they react the same. They look the same. There are about 100 known elements. They are all listed in the Periodic Table of Elements. Example: Atoms of gold are the same as all atoms of gold. However, atoms of gold are different than atoms of silver or lead. Gold, silver and lead are all elements.

Symbols for the Elements:

The names were originally from Latin which is why some of them do not seem to make sense. For this unit you should k now the first 20 elements. Identify the ones that do not seem to match their names.

Compound- a composition of various elements.

Example: Water is a compound made up of 2 atoms of the element Hydrogen and 1 atom of the element Oxygen atom.

Types of Mixtures:

Heterogeneous mixture a mixture which is not the same throughout. Chocolate chip cookies are heterogeneous because you can take two samples at different places and they may not be the same, one sample may not include a chip.

Ice cream with raisins

Brownies with nuts.

3 Li 6.941 Homogeneous mixture a mixture which is the same throughout. A sample taken at any place will be the same.

Examples: Vanilla ice cream, plain bread.

Types of mixtures including a liquid:

Solutions the homogeneous mixture of a liquid and dissolved solid or two liquids.

Examples:

sugar and water most drinks are mostly sugar dissolved in water alcohol in water alcoholic drinks are mostly water with sugar and alcohol dissolved gasoline and Styrofoam will mix to create a homogeneous liquid Suspensions this type of heterogeneous mixture will separate into its components unless

Examples:

Sand and water

Water and oil.

Here you see Liquids which have separated on the left and liquids that do not separate on the right. From: http://chemistry.tutorvista.com/physical-chemistry/dilute-solution.html Miscible two liquids that will mix and stay mixed. Immiscible two liquids that will not mix but will separate if left alone.

Colloids - a homogeneous substance consisting of large molecules or ultramicroscopic particles of one

substance dispersed through a second substance. Colloids include gels and emulsions; the particles do not settle

and cannot be separated easily.

Types of observations:

Quantitative assigning a numerical value to describe an observation Qualitative describing an observation with a description

Example: Length of a trip:

Quantitative: 150 miles

Qualitative: Longer than from here to New York City.

Qualitative only: Scent, Taste,

When measuring scents or tastes it is very difficult to assign a number. These measurements are almost strictly

qualitative. People that do this for a living might taste test ice cream, wine, beer, or any food type item.

Testing Wine Testing Beer

Can you tell the difference between the tea?

Smell Testing for Deodorant.

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