Combining Atoms Through Chemical Reactions Chemical Reactions The

Combining Atoms Through Chemical Reactions

Chemical Reactions • The changing of one or more substances into other substances is called a chemical reaction. • Chemical reactions that occur in living organisms are called metabolism.

Atoms and Energy Levels • Atoms have energy levels. They like to have full energy levels for a more stable electron configuration. • The first energy level (the one nearest the nucleus) can hold up to 2 electrons. The second energy level has eight electrons to be full. The third energy level holds 8 electrons until you get above atomic number 18. • Above atomic number 18 the third energy level can hold up to 18 electrons. For our purposes 2 -8 -8 will suffice since we will not be working with the larger atoms.

Creates a Tendency to Bond • Atoms that do not have full outermost energy levels bond to other elements. • Atoms combine together by forces called chemical bonds. • There are two main types of chemical bonds: ionic bonds and covalent bonds

Valence Electrons • The electrons in the outermost energy level are called valence electrons. • It is the valence electrons that determine which atoms will lose electrons and which atoms will gain them.

Compounds • Compounds and molecules are formed when two or more elements combine with each other. • The new compound or molecule will not have the same properties as the elements that made it.

Examples of Compounds • Water is made of hydrogen and oxygen. Neither hydrogen nor oxygen have the properties of water. • Salt is compound that is a combination of sodium and chlorine. Salt does not have the properties of the elements that formed it.

Molecules • A molecule is the smallest unit of a compound. • What is the smallest unit of an element? • In some cases, two atoms of the same element will form a molecule. • They are called diatomic molecules.

Chemical Formulas • Every element is represented by a symbol. • A chemical symbol starts with a capital letter. If there is a second letter it is a lowercase letter. • A subscript is written after the symbol to show many atoms of that element exist in the molecule.

What do these formulas mean? • • Cl 2 H 2 O Al 2 O 3 Fe 2 O 3 O 2 N 2 Which of these are diatomic molecules? Can there be two different letters in a diatomic molecule?

Remember the Periodic Table • Horizontal row are called periods. • The vertical columns are called groups or families because they have similar properties. • The periodic table consist of metals, nonmetals and metalloids.

The Periodic Table

Metals • Metals have 1, 2, or 3 valence electrons in their outermost level. • They tend to lose or transfer electrons to other atoms easily. • Metals conduct heat and electricity. • Metals are usually ductile meaning they can be drawn out into wire and also malleable (having the ability to be hammered into sheets).

Nonmetals • Except for hydrogen and helium, the atoms of nonmetals have four or more electrons in the outermost energy level. • They do not lose electrons easily but often gain electrons from metals or transition metals. • The noble gases are nonmetals with full outermost energy levels and so are fully satisfied and do not react with other elements.

Ionic Bonding • Ionic bonding is a type of chemical bond where electrons are transferred from one atom to another. • This makes them become charged atoms called ions. Negative ions are called anions and positive ions are called cations. In chemical formulas, the positive ions are always written first. These ions attract each other and form ionic compounds.

Ionic Compound

Covalent Bonding • Covalent bonds form when two atoms share electrons rather than transfer them. • Sometimes these electrons are not shared equally but are attracted to one end of the atom more so than the other creating a polar molecule.

Covalent Molecule

Polar Molecules • In a polar molecule, the electrons will spend more time in the area of stronger attraction for them. • A polar molecule will have a positive end a negative end. • Water, a polar molecule, is negatively charged on its oxygen end and positively charged on its hydrogen end.

Water, A Polar Molecule

Water Gets Together • The positive end of a water molecule is attracted to the negative end of another water molecule creating a hydrogen bond between them. • Other polar molecules may experience this type of bonding as well.

Metallic Bonds • In metals, metallic bonds are often formed. The valence electrons are shared by all the atoms, not just by adjacent atoms. It is like a group of positive ions floating in a sea of negative electrons. • Because the electrons in metallic bonds are shared by all of its atoms, it allows for the flow of electricity through their atoms.

PH Readings • A ph scale measures the hydrogen and hydroxide ions in solutions. A ph reading of 7 is neutral like distilled water. • A ph reading below 7 is acidic and above 7 is basic (more alkaline). • Rainwater is slightly acidic having a ph from 5. 0 to 5. 6.

Special Solutions • An acid is a solution containing a substance that produces hydrogen ions (H+) in water. • Bases produce hydroxide ions (OH-) in solution. A base can neutralize an acid by combining with hydrogen ions of the acid to form water.

Conclusion • Chemical reactions take place because of an atom’s need to have full energy levels. • Covalent bonding, the sharing of electrons and ionic bonding the transfer of them are common types of bonds. Metallic bonds share their electrons with all of the atoms of the compound. • Solutions like acids and bases stimulate chemical reactions.