The Atom Matter is anything that has mass and takes up space Living and nonliving things are made up of tiny units called atoms. The center core is called the nucleus. Chemistry really involves electrons

The Atom The nucleus is made up of particles called protons and neutrons Protons have a positive charge (+1) and neutrons have no electrical charge (0). Negatively charged particles, called electrons (-1) revolve around the nucleus at different distances from the nucleus.

The Atom The electrons move in paths called shells or energy levels. Atoms have the same number of electrons and protons. Therefore, they are electrically neutral (have no electrical charge).

Elements There are about 100 different kinds of atoms known to scientists today. A substance made up entirely of one kind of atom is called an element. Ninety-two elements occur naturally and the others were made up in a laboratory. Elements differ from one another in their proton, neutron, and electron number.

The Periodic Table of Elements

Most Common Elements Element Symbol Carbon C Hydrogen H Oxygen O Nitrogen N Sulfur S Phosphorus P Magnesium Mg Iodine I Iron Fe Calcium Ca Sodium Na Chlorine Cl Potassium K Zinc Zn Most Common Elements

Elements An element cannot be broken down into any other substance or matter. Pure silver is an element. It is made up only of silver atoms. When you break down a silver atom, you get electrons, protons, and neutrons.

Element Symbols Each element is represented by a symbol made up of one or two letters.

Compounds A compound is formed when two or more elements combine chemically.

Compound Properties The properties (characteristics) of compounds are quite different from the properties of the elements of which they are composed. For example, table sugar is made up of the elements carbon, hydrogen, and oxygen. Carbon is a black solid, and hydrogen and oxygen are colorless gases. However, when they combine chemically they form a white granular substance.

Compounds Elements combine to form compounds by a process called chemical bonding. The formation of a chemical bond involves either the transfer of electrons from one atom to another, or the sharing of electrons between atoms.

Chemical Bonding

Molecules A molecule of a particular compound is made up of definite numbers and kinds of atoms bonded (joined) together. A molecule of water contains two hydrogen atoms and one oxygen atom bonded together. Two atoms of hydrogen bond together form a molecule of hydrogen.

Ions An ion is an atom that has gained or lost an electron. Ions are formed during chemical bonding that involves the transfer of electrons. When electrons are transferred from one atom to another, both atoms become electrically charged. The atom that loses electrons becomes positively charged. The atom that gains electrons becomes negatively charged. The ions with opposite electrical charges are attracted to one another.

Ionic Bonds A chemical bond formed when atoms lose or gain electrons is called an ionic bond.

Covalent Bonds Covalent bonds are formed when atoms produce compounds by sharing electrons. When making hydrogen gas, one molecule of hydrogen gas is formed when two hydrogen atoms join by sharing electrons.

. Chemical Formulas A chemical formula represents the chemical makeup of a compound. It shows the numbers and kinds of atoms present in a compound. It is a kind of “shorthand” that scientists use.

Formula Examples H2O (water) SO2 (sulfur dioxide) CO2 (carbon dioxide) The chemical formula for sugar is C6H12O6 This means that in one molecule of sugar there are six carbon atoms, twelve hydrogen atoms and six oxygen atoms. H2O (water) SO2 (sulfur dioxide) CO2 (carbon dioxide)

Structural Formulas A formula can also show the kinds, numbers, and arrangement of atoms. This is called a structural formula. Here is the structural formula of Hydrogen.

Equations Equations are used to describe chemical reactions. The substances that start the reaction are called the reactants. The reactants are placed on the left side of the equation. The substances formed by the reaction are called the products. The products are placed on the right side of the equation. The arrow means “to make” or “to form”.

Equations Reactions may be represented either by words or formulas. The word equation for aerobic respiration is: (enzymes) SUGAR + OXYGEN  ENERGY + CARBON DIOXIDE + WATER An equation using formulas instead of words is called a chemical equation. The chemical equation for aerobic respiration is: C6H12O6 + O2  6H2O + 6CO2

Organic and Inorganic Compounds Living things are made up of inorganic and organic compounds. Compounds that do not contain both carbon and hydrogen are called inorganic compounds. The principal inorganic compounds found in living things are: water salts inorganic acids Inorganic bases

Organic and Inorganic Compounds Organic compounds are compounds that contain both carbon and hydrogen. The classes of organic compounds found in living things are: Carbohydrates Proteins Lipids Nucleic acids