Chemical Bonds & Reactions

Chemical Bond A force of attraction that holds two atoms together involves the sharing or transfer of valence electrons Valence Electrons – the electrons in the outermost energy level of an atom This Lithium Atom has one valence electron

How Many Valence Electrons? Hydrogen Lead Xenon Sulfur Rubidium 1 Valence Electron 4 Valence Electrons 8 Valence Electrons 6 Valence Electrons 1 Valence Electron

The Octet Rule Atoms will combine to form compounds in order to reach eight electrons in their outer energy level. This makes them stable. –Atoms with less than 4 electrons tend to lose electrons. –Atoms with more than 4 electrons tend to gain electrons. Hydrogen and Helium only need 2 electrons to be stable.

The Octet Rule In Action Notice how the sodium atom has one valence electron. It is this electron that it will try to get rid of according to the Octet Rule. Notice how this chlorine atom has seven valence electrons, one away from eight. It will try to gain one more according to the Octet Rule Where do you think Chlorine finds that one electron that it needs?

2 Types of Chemical Bonds Covalent Ionic

COVALENT BOND A force that bonds two atoms together by a sharing of electrons Each pair of shared electrons creates a bond Usually occurs between atoms of non-metals Example – Water (H 2 O)Water (H 2 O) OHH

Which different groups or families of elements will most-likely interact to create these types of bonds? IONIC BONDS - The force of attraction between oppositely charged ions. Occurs after a transfer or loss/gain of electrons Usually form between atoms of metals and atoms of non- metals Example - Sodium Chloride (NaCl)Sodium Chloride (NaCl) Cl Na 1- 1+

Symbol = O 2+ Ion Charged particle that typically results from a loss or gain of electrons Now that this atom of oxygen just gained an electron, it is no longer neutral or an atom. It is now considered an ion (anion). This ion has more electrons (9) than protons (8). + - = 8 96 Symbol = O 1- Now that three electrons were lost, the number of electrons (6) and protons (8) is still unbalanced; therefore, it is still an ion, but now it is specifically referred to as a cation. Currently, this atom of oxygen is neutral because it has an equal number of electrons (8) and protons (8). Symbol = O

Cations and Anions Cations Form when an atom loses one or more electrons. Has more protons than electrons and is positive. Metals tend to become cations Anions Form when an atom gains one or more electrons. Has more electrons than protons and is negative. Nonmetals tend to become anions.

Results of Bonding Molecule Two or more atoms are chemically combined. Example H 2, F 2, O 2, N 2, CH 4, CO Compound A pure substance composed of two or more different elements (atoms) that are chemically combined Examples: CO, NO 2, NaCl All compounds are molecules.

Molecule, Compound, or Both? H 2 Hydrogen NO 2 Nitrogen Dioxide Cl 2 Chlorine O 2 Oxygen NO Nitric Oxide CO 2 Carbon Dioxide N 2 Nitrogen H 2 O Water CH 4 Methane