Chemical Bonds Ionic Bonds

Valence Electron and Bonding What are valence electrons? Electrons that have the highest energy level and are held more loosely The number of valence electrons in an atom of an element determines many properties of that element, including the ways in which the atom can bond with other atoms

Valence Electrons What is an electron dot diagram? The symbol for the element surrounded by dots Each dot stands for one valence electron Each element has a specific number of valence electrons Atoms are more stable and less likely to react when they have eight valence electrons These elements do not easily form compounds

Valence Electrons How do elements become stable? Atoms usually react in a way that makes each atom more stable 1) They either increase their valence electrons to eight 2) Or, the atom gives up loosely held valence electrons Atoms that react by loosing valence electrons become chemically bonded with other atoms A chemical bond is the force of attraction that holds two atoms together as a result of the rearrangement of electrons between them When atoms bond, electrons are transferred from one atom to another

Periodic Table How is the periodic table organized? By atomic number, the arrangement of electrons in atoms, and the number of protons in the nucleus of an atom As the atomic number increases, the number of electrons also increases A period ends when the highest energy level has eight electrons The elements within a group always have the same number of valence electrons, therefore they have the same properties

Periodic Table Noble Gases: Group 18 and atoms of these elements have eight valence electrons which is why they do not react easily, except for Helium which has 2 Reactive Metals and Nonmetals: Noble gases in group 17, only have seven valence electrons. A gain of just one more electron gives these atoms the stable number of eight electrons. Metals in Group 1 have only one valence electron, therefore react by losing an electron to become more stable.

Periodic Table Other Metals: How reactive a metal is depends on how easily its atoms lose valence electrons. Atoms in group 2 are more likely to lose electrons than in group 3-12. Other Nonmetals: All of the nonmetals have four or more valence electrons, so react by gaining electrons to become more stable. Nonmetals can combine with other nonmetals by sharing electrons. Hydrogen: Hydrogen is located in Group 1 because it only has one valence electrons, but it is a nonmetal so it reacts a lot differently then other elements in Group 1

Ionic Bonding Atoms with 5, 6, or 7 valence electrons usually become more stable when the number increases to 8 Atoms with 1, 2, 3, or 4 valence electrons usually become more stable when it loses electrons When these two type of atoms combine, they form an ionic bond How does an ion form? When an atom loses an electron, it loses a negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and become a negative ion. What is a polyatomic ion? Ions that are made of more than one atom. It is a group of atoms that react as a unit.

Ionic Bonding Sodium has 1 valence electron and chlorine has 7 valence electrons When sodium’s valence electrons are transferred to chlorine, both atoms become an ion The sodium become the positive ion and chlorine become the negative ion What is an ionic bond? The attraction between two oppositely charged ions Ionic bonds form as a result of the attraction between positive and negative ions A compound that consists of a positive ion and a negative ion like sodium chloride, is called an ionic compound

Chemical Formulas and Names What is a chemical formula? A combination of symbols that shows the ratio of elements in a compound Ex. MgCl2 When ionic compound forms, the ions come together in a way that balances out the charges on the ions Two chloride ions, each with a charge of -1 will balance the charge on the magnesium ion. That is why the formula for magnesium chloride is MgCl2. A subscript tells you the ratio of elements in the compound. The ratio for magnesium chloride is 2 to 1.

Naming Ionic Compounds How do you name ionic compounds? For an ionic compound, the name of the positive ion comes first, followed by the name of the negative ion. The name of the first ion is usually a metal, unless a polyatomic ion exists such as NH4 which is ammonium chloride Rule 1-If the negative ion is a single element, the end of the naming of the compound is IDE EX - Sodium Chloride Rule 2-If the negative ion is polyatomic, its name usually ends in ATE or ITE

Properties of Ionic Compounds What are some properties of ionic compounds? Hard Brittle Crystals High Melting Points When dissolved in water or melted, they conduct electricity. The ions form a orderly, three dimensional crystal arrangement When ionic crystals dissolve in water, the bonds between ions are broken