Chemical Bonds Regents Review Book: Chapter 4 Chapter 5 – Page 157

Types of Chemical Bonds We will study 4 types of chemical bonds: Ionic Bonds Bonds between metals and non-metals Electrons are transferred Covalent Bonds Bonds between two non-metals Electrons are shared Metallic Bonds Bonds between two metals Intermolecular Bonds Bonds between molecules

Chemical Reactivity Some chemicals are reactive and some are not  Name the most reactive metal on the periodic table:____________________  Name the most reactive non-metal on the periodic table:____________________  Name the non-reactive gases on the periodic table:___________________________

Chemical Reactivity Why are the noble gases not reactive? ____________________________________ ____________________________________ Draw the Bohr model of the outer valence shell of Neon:

Chemical Reactivity If the noble gases are not reactive due to their outer shell configuration, then the alkali metals and halogens must be very reactive because: ______________________________________

Chemical Reactivity Draw the Bohr model outer shell valence configurations for sodium and fluorine: SodiumFluorine If sodium loses its one valence electron, will it have a full outer energy level? _______ If fluorine gains one valence electron, will it have a full outer valence energy level? ________

Chemical Reactivity Does having a full outer valence electron configuration make an atom more stable? Why? OCTET RULE: a concept of chemical bonding theory that assume that atoms want to have the full electron configuration of the noble gases: 8 outer (valence) electrons

Chemical Reactivity Why doesn’t sodium try to gain seven more electrons rather than giving one away? ______________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Why can fluorine gain electrons?

Chemical Reactivity Please note: Hydrogen can gain or lose an electron Helium is stable because its valence shell is full with only two electrons (it only has 2 protons). Lithium (three protons) and Beryllium (4 protons) will also be stable with only two electrons in their valence shell.

IONS Charged particles are called IONS  Loss of an electron makes the atom more positive so it is called a positive ion. In our example, sodium loses an electron. The way to write a positive ion is as follows: Na +1 Symbol of elementCharge on the ion The EQUATION for this reaction is: Li → Li + + e -

Cation – Positively Charged Ion

IONS  Gain of an electron makes the atom more negative, so it is called a negative ion. Cl -1 The equation for this reaction is: F + e - → F - Symbol of element Charge on the ion

Anion – Negatively Charged Ion

Valence Electrons  Electrons that are found in the outermost shell of an atom; they determine the atom’s chemical properties because: Valence electrons are the electrons involved in chemical bonding! Inner electrons are not involved in bonding

Transition Elements Not all elements must have a noble gas configuration to be stable – these are called the transition elements. Many transition metals are stable even though they do not have noble gas configurations. Ex: Copper can give up one or two electrons when bonding; both cations are stable even without a noble gas configuration. Color of copper when it gives up one electron Color of copper when it gives up two electrons

IONS vs. ATOMS Atoms and Ions have different properties Example: Sodium metal and chlorine gas are very reactive and dangerous. Sodium chloride (NaCl) is an ionic compound that is NOT dangerous BECAUSE IONS HAVE DIFFERENT PROPERTIES THAN THEIR PARENT ATOMS

General Information About Bonds Chemical bonds have stored (potential) energy Energy must be absorbed to break a chemical bond Energy is released during bond formation

Ionic Bonds When a metal atom transfers electrons to a non-metal atom, an IONIC BOND is formed The two atoms are attracted by their opposite charges

Ionic Bonds Do the two atoms in the previous slide have fuller outer octets? Does this make sodium chloride stable or unstable?

Bond Character An ionic bond occurs when the electronegativity difference between its atoms is 2.0 or greater. Example: Electronegativity of Sodium:___________ Electronegativity of Chlorine:___________ Difference in Electronegativity___________ Based on the above information, is this an ionic bond?_______________

Ionic Bond Summary 1. Formed by the ___________________of electrons. 2. Form when a ___________________ion and _____________________ion attract each other. 3. Have an electronegativity difference of _________or more.

Ionic Salts Atoms in an ionic compound tend to arrange themselves in specific orderly patterns (crystalline structures) and form salts

Ionic Salts Salts are Hard and Brittle (pg 173) Crystals are arranged in repeating patterns, which form layers Each cation is positioned next to an anion The attractive force between these oppositely charged ions make it very strong It takes a lot of energy to break these bonds

Properties of Ionic Substances (salts) MEMORIZE THE FOLLOWING!!! 1. All are solid at room temperature. 2. Are hard and brittle; should not break easily. If it does break, it is into smaller crystals. 3. Have high melting and boiling points. 4. Ionic compounds that are melted will conduct electricity. 5. Ionic compounds dissolved in water will conduct electricity. 6. Will dissolve in polar compounds.