Chapter 7: Foundations 0f Chemistry

Matter is anything with mass/volume. Matter is made of elements. Mass is the amount of material that is in an object. Weight is the effect of gravity upon an object. Volume is the amount of space taken up by an object or substance. Elements are substances that cannot be broken down into simpler substances by ordinary means. Each element is composed of individualized particles called atoms.

Scientists have developed a model to explain observations about matter. 150 years ago, John Dalton developed this model. According to the model: “All matter is made of particles so small that they cannot be seen even with a powerful microscope. There are about 100 kinds of these particles but when they combine, they make up the thousands of substances that occur in the Earth’s crust.” All matter is composed of elements!

Atoms are the smallest part of an element that retains the properties of the element. All atoms are comprised of protons, neutrons and electrons. Protons have a positive charge, electrons have a negative charge and neutrons have a neutral charge.

This is the first picture ever captured of an individual atom!

The Atomic Number is the number of protons in an atom. The number of electrons in an atom always equals the number of protons in the nucleus The number of neutrons isn’t standard; however, the mass number of the element gives the average number of protons and neutrons. Neutrons = mass number – atomic number

Although atoms are mostly empty space, scientists have discovered that electrons hang out in energy levels. Each energy level can only hold a specific number of electrons. They are 2, 8, 18, 32, 64. The outermost electrons are called valence electrons and give each type of atom unique chemical properties.

There are 92 naturally occurring elements. On the Periodic Table, elements are categorized vertically by chemical properties and horizontally by atomic number.

Atoms are considered neutral because the number of positively charged protons is equal to the number of electrons, which are negatively charged. Atoms that gain or lose electrons from their outermost energy levels are called ions.

Isotopes Isotopes are atoms of the same chemical element with different mass numbers. They can be produced many ways, but usually within a nuclear reactor or in a particle accelerator. In the example above, Hydrogen has three isotopes. Uranium has also has three isotopes. Isotopes are usually radioactive and sometimes the chemical reactions they participate in occur slower than normal.

Most substances are compounds. Compounds are 2 or more elements chemically combined. The smallest part of a compound that has the properties of the compound is a molecule.

Chemical Reaction: the change of one or more substances into other substances is called a chemical reaction. These reactions are described by chemical equations. For example, 2H2 + O2 2H2O In chemical reactions, everything to the left of the arrow are the reactants and everything to the right of the arrow are the products. You must have the same amount of matter on both sides of the equation. This fundamental fact is called the Law of Conservation of Matter.

 The pH Scale is based upon the amount of hydrogen ions in a solution. This amount is referred to as the concentration. A value of 7 is considered neutral. The lower the number, the more acidic the solution. The concentration of hydrogen ions is commonly expressed in terms of the pH scale. Low pH corresponds to high hydrogen ion concentration and vice versa. A substance that when added to water increases the concentration of hydrogen ions(lowers the pH) is called an acid. A substance that reduces the concentration of hydrogen ions(raises the pH) is called a base. Finally some substances enable solutions to resist pH changes when an acid or base is added. Such substances are called buffers. Buffers are very important in helping organisms maintain a relatively constant pH.

Acids are solutions containing a substance that produces hydrogen ions in water. The concentration of hydrogen ions in a solution is very important for living things. This is because, since the hydrogen ions are positively charged they alter the charge environment of other molecules in solution. By putting different forces on the molecules, the molecules change shape from their normal shape. This is particularly important for proteins in solution because the shape of a protein is related to its function. Bases are substances that produce hydroxide ions in water. Bases can neutralize acids.

A molecule consists of at least 2 atoms, in a definite concentration. Compounds can have properties unlike elements from which it’s made. Basically, anything you can combine from the Periodic Table of Elements can make compounds. Water: hydrogen and oxygen Salt: sodium and chlorine Bicarbonate of Soda ( NaHCO3) Iron Oxide Carbon Dioxide Calcium Carbonate

This model of a molecule becomes more concrete when we bounce a laser off of this single compound for twenty hours and image it.

Mixtures contain elements or compounds that keep their properties. Most mixtures can be physically separated easily. Saltwater Koolaid: a solution Oil/Vinegar: a suspension Paint: a colloid, materials evenly distributed

Mixtures MIXTURES : Combination of two or more substances that are not chemically combined – No new substance formed – Do not exist in fixed proportions to each other – They just mix – Most natural substances are mixtures – Can be physically separated into pure compounds or elements – Can be separated by mechanical means – Physical properties can change – Any combination of solid, liquid or gas can be a simple mixture MIXTURES MAY BE HOMOGENEOUS OR HETEROGENEOUS

SOLUTIONS are homogeneous mixtures: – A solution is a mixture of two or more substances in a single phase – At least two substances must be mixed in order to have a solution – The substance in the smallest amount and the one that DISSOLVES is called the SOLUTE – The substance in the larger amount is called the SOLVENT - it does the dissolving – In most common instances water is the solvent – The gases, liquids, or solids dissolved in water are the solutes COLLOIDS are another type of homogeneous solutions with a bigger particle size – Colloid particles may be seen in a beam of light such as dust in air in a "shaft" of sunlight – Milk, fog, paint and jello are examples of colloids

COMPARE & CONTRAST MIXTURES & COMPOUNDS Mixture Compound Not chemically combined Combine chemically, forming molecules Can combine in any proportion Combine in set proportions Separated physically Separated chemically

States of matter in solution : Example gas in gas: air ( N 2, O 2, Ar, CO 2, other gases) gas in liquid: soda pop (CO 2 in water) liquid in liquid: gasoline (a mixture of hydrocarbon compounds) solid in liquid: sea water ( NaCl and other salts in water) gas in solid: H 2 in platinum or palladium liquid in solid: dental amalgams ( mercury in silver) solid in solid: alloys ( brass, (Cu/Zn), solder (Sn/Pb)