Elements and Compounds Chapter 2 Elements and Compounds

The Particle Theory of Matter All matter is made up of tiny particles. All particles of one substance are the same. Different substances are made up of different particles. The particles are always moving. The more energy the particles have, the faster they move. There are attractive forces between the particles. These forces are stronger when the particles are closer together.

There are attractive forces between particles There are attractive forces between particles. In a solid, the attraction between particles is strong so the matter holds its shape. The particles are still moving, but they are not able to slide past each other. They just vibrate. In a liquid the attractive forces are not as strong. The particles are able to move past each other and slide around. The forces are strong enough to keep the particles from flying away. In a gas, the attraction between particles is so weak that they fly in every direction filling the container that they are held.

As well as classifying matter as solids, liquids, and gasses, we can classify matter as either a mixture or a pure substance. A pure substance is made from only one type of particle. These specific particle types give the substance its physical characteristics such as odor, color, hardness. A mixture contains two or more pure substances. (See Fig. 1 pg. 45)

A homogeneous mixture has two substances where the particles are blended completely. To the eye, the mixture appears to be pure substance. When the particles stay intermixed and don’t settle into layers we call the homogeneous mixture a solution.

A heterogeneous mixture has large clumps of particles that don’t fully separate and get intermixed with the other substance. Examples of heterogeneous mixtures are salad dressing, oil and water, pizza, etc.

Elements and Compounds Elements are pure substances that cannot be broken down into simpler substances. Compounds are pure substances that contain 2 or more elements in a fixed proportion. They are formed when elements combine together in chemical reactions.

Atoms and Molecules The particles that make up the particle theory are now known as atoms. Each elements is made up of only one kind of atom. When 2 or more atoms join together, they form a molecule. Molecules can contain only one type of atom or many different atoms. Different molecules can also be made up of the same elements but in different proportions. Video

What makes up an atom? Three types of particles make up an atom; these are called subatomic particles. Protons – positive charge, found in the nucleus. Neutrons – no charge, found in the nucleus. Electrons – negative charge, found orbiting the nucleus.

Properties of Metals Metals are good conductors of heat and electricity. Metals are shiny. Metals are ductile? (can be stretched into thin wires). Metals are malleable? (can be pounded into thin sheets). A chemical property of metal is its reaction with water which results in corrosion.

Properties of Non-Metals Non-metals are poor conductors of heat and electricity. Non-metals are not ductile or malleable. Solid non-metals are brittle and break easily. They are dull (not shiny). Many non-metals are gases. Sulfur

Properties of Metalloids Metalloids (metal-like) have properties of both metals and non-metals. They are solids that can be shiny or dull. They conduct heat and electricity better than non-metals but not as well as metals. They are brittle and not ductile Silicon

Assignment Read Pgs. 44 – 47 & 50-51 Answer Questions 1-4 pg. 47 and 1-3 pg. 51.

C Cu Chemical Symbols Carbon Copper All elements have their own unique symbol. It can consist of a single capital letter, or a capital letter and one or two lower case letters. Elements have their name for a variety of reasons. Some are named after mythology, countries, scientists or in Latin or Greek. C Carbon Cu Copper

Chemical Formulas When atoms of different elements combine, they form compounds. A chemical formula is the combination of symbols that represents a particular compound. (Table 2 pg. 59). If there is more than one atom of the element in a compound, the symbol is followed by a number (called a subscript). Eg. H2O = Water (2 atoms of Hydrogen and 1 atom of oxygen)

Names and Formulas for Compounds Chemical formulas are used to represent compounds, but how are the compounds made? How do we know that sodium and chlorine combine to make NaCl and not Na2Cl or NaCl2, etc.?

Rules For Combining Elements Rule 1: Metals combine with non metals in many compounds. Rule 2: Write the name of the metal first and the non metal second. Rule 3: Change the ending of the non metal to “ide.” Rule 4: Each atom has its own combining capacity. Rule 5: Atoms combine so that each can fill its own combining capacity.

Combining Capacity Combining capacity is the ability of an element to combine with other elements. It is a numerical value given to each metal and non metal to explain the compounds that they form. For example. Both sodium and chlorine are assigned a combining capacity of 1. This means that each of these elements can make 1 connection. Thus the formula for this compound is NaCl.

Combining Capacity The combining capacities for some metals and non metals are in Tables 2 & 3 on pg. 64. When naming the compound, drop the last few letters of the non-metal and replace it with “ide.” NaCl = sodium chloride

Combining Capacity There are some elements that have more that one combining capacity. When writing the names (not the symbols) for these compounds, the combining capacity must be written in Roman Numerals between the metal and non metal. Example: Iron (II) Oxide – FeO Iron (III) Oxide – Fe2O3

Assignment Read Pgs. 58-61 & 64-65. Answer Questions pg. 59 (1-5), pg. 61(1-4) & Pg. 65.(1-5).

Ch. 2 Review Pg 76-77 Do the following questions: 2-5 & 8-12