The 8 valance electrons in the noble gases make them chemically stable All other Elements “want” their valence electron structure to look like a noble gas Atoms will react with other atoms to achieve this stable octet..

Atoms tend to gain, lose or share electrons so as to have 8 electrons in their outer energy level. (Look like their nearest noble gas) Octet Rule

Types of Chemical Bonds IONIC COVALENT METALLIC HYDROGEN

IONIC BONDING When an atom of a nonmetal takes one or more electrons from an atom of a metal allowing both atoms to end up with eight valence electrons

Na Ca Al P S F C Gain – lose 4 electrons Gain 3 electrons Gain 2 electrons Lose 1 electron Lose 2 electrons Lose 3 electrons Gain 1 electrons How many electrons would each of the following elements need to gain or lose to look like the nearest noble gas?

ION An atom with an unbalanced number of protons and electrons. This causes the atom to have an electrical charge. The chemical and physical properties of the ion are different from that of the neutral atom

Ionic compounds result when metals react with nonmetals Metals lose electrons to match the number of valence electrons of their nearest noble gas Positive ions form since the number of electrons are now less than the number of protons Group 1 metal  ion 1+ Group 2 metal  ion 2+ Group 13 metals  ion 3+ Transition metals  vary Formation of Ions from Metals

CATIONS Metals will tend to lose electrons and become POSITIVE CATIONS Normal sodium atom loses one electron to become a sodium cation

Nonmetals gain electrons to match the number of valence electrons of their nearest noble gas Negative ions form since the number of electrons is now more than the number of protons Group 15 nonmetal  ion 3- Group 16 nonmetal  ion 2- Group 17 nonmetal  ion 1- Formation of Ions from Nonmetals

ANIONS Nonmetals will tend to gain electrons and become NEGATIVE ANIONS Normal chlorine atom gains an electron to become a chloride anion

IONic bonding Always formed between metals and non-metals [METALS ] + [NONMETALS ] - Lost e - Gained e -

IS THIS COMPOUND AN IONIC COMPOUND?METAL NONMETAL YES

IONIC BOND FORMATION When neutral atoms come near each other. Electron(s) are transferred from the Metal atom to the Nonmetal atom. They then stick together because of electrical attraction.

Oxidation Number The charge on the ion. It is shown with a superscript written after the element symbol.

Na +1 is a sodium ion. The +1 means it has lost one electron and now has a charge of positive 1 Mg +2 is a magnesium ion. The +2 means it has lost two electrons and now has a charge of positive 2 Oxidation Numbers

S -2 is a sulfide ion. The -2 means it has gained two electrons and now has a charge of negative 2 Cl -1 is a chloride ion. The -1 means it has gained one electron and now has a charge of negative 1 Oxidation Numbers

POLYATOMIC IONS: A group of atoms that act like one ion NH 4 +1 ammonium ion CO 3 -2 carbonate ion PO 4 -3 phosphate ion Oxidation Numbers

When forming an ionic compound the number of electrons lost by the metal has to balance the number of electrons gained by the nonmetal. Subscripts allow you to balance the oxidation numbers so that the number of electrons lost by the metal equals the number of electrons gained by the nonmetal. IONIC BONDING

The shorthand for a compound is a formula. To write a formula, write the positive symbol first and the negative symbol second. Put the oxidation numbers for each as superscripts. Use subscripts to tell how many of each kind of atom you are using to balance the transfer of electrons gained and lost. Writing Formulas

What is the formula for the compound of Nitrogen and Magnesium? Mg N +2− Mg atoms lose 2 electrons each: Total of 6 electrons 2 N atoms gain 3 electrons each: Total of 6 electrons

When finding the written name for a compound, write the name of the positive ion first. Next write the name of the negative ion but drop the ending on the negative ion and replace it with ‘ide’. For example: Na 2 S = sodium sulfide Do not change the name of a polyatomic ion. Naming Ionic Compounds

 POLYATOMIC IONS ACT JUST LIKE ANY OTHER ION WHEN BONDING IONIC BONDING

SODIUM SULFATE

IONIC BONDING

Properties of Ionic Compounds Crystal Lattice: The ions form a regularly repeating pattern in the solid. Rigidity: The crystal lattice allows for strong bonds among the ions in the solid.

Crystalline Structure The POSITIVE CATIONS stick to the NEGATIVE ANIONS

High melting points. Strong bonds hold the solid together. Ionic solids are insulators: The ions are locked in place. Melted ionic compounds conduct: When melted, the ions can move around. Dissolved in water they conduct: The ionic compounds are pulled apart by the water molecules. Properties of Ionic Compounds

Ionic solids are brittle

Strong Repulsion breaks crystal apart.

COVALENT BONDING When an atom of one nonmetal shares one or more electrons with an atom of another nonmetal so both atoms end up with eight valence electrons

COVALENT BOND FORMATION Sharing must always be equal. Each atom must contribute the same number of electrons

Covalent Bond A single bond is the sharing of two valence electrons. One from each atom. A double bond is when atoms share two pair of electrons for a total of 4 electrons. A triple bond is when atoms share three pair of electrons for a total of 6 electrons.

COVALENT BONDING IS THE COMPOUND A COVALENT COMPOUND?NONMETAL NONMETALYES

Modeling Covalent Molecules Lewis Dot Structures The Symbol represents the nucleus and inner electrons of the atom. Dots or X’s represent the valence electrons. C

Methane CH 4 This is the finished Lewis dot structure How did we get here? H H C H H ✖ ✖ ✖ ✖

All other Elements “want” their valence electron structure to look like a noble gas The number of electrons an atom needs is the total number of bonds it can make. How many bonds can each of the following elements form? H O F N Cl C one two one three one four

Methane CH 4 This is the finished Lewis dot structure How did we get here? H H C H H ✖ ✖ ✖ ✖

Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons FF

Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons FF

Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons FF

Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons l Both end with full orbitals FF

Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons l Both end with full orbitals FF 8 Valence electrons

Covalent bonding l Fluorine has seven valence electrons l A second atom also has seven l By sharing electrons l Both end with full orbitals FF 8 Valence electrons

Water Every atom has full energy levels H O H

Carbon dioxide l Requires two double bonds l Each atom gets to count all the electrons in the bond O CO

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the electrons in the bond O CO 8 valence electrons

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the electrons in the bond O CO 8 valence electrons

Carbon dioxide l The only solution is to share more l Requires two double bonds l Each atom gets to count all the electrons in the bond O CO 8 valence electrons

Modeling Covalent Molecules Structural Formula Uses a line to indicate a bond Each line stands for 2 shared valence electrons

HHO HHO ✖ ✖ Lewis Dot Structural Formula

Formula and Name Draw Lewis Dot Diagram Write the formula, more metal first, with subscripts Write the name using “ide” ending Add the prefixes mono, di, tri and tetra to show one, two, three or four atoms. Carbon Dioxide Dihydrogen Monooxide

Covalent Bonds Types of Covalent Bonds NON-Polar bonds –Electrons shared evenly in the bond. –Electrons spend an equal amount of time around each element. –Element molecules: H 2 O 2 N 2

Types of Covalent Bonds Polar bond  One element has more of an attraction for electrons than the other.  Electrons unevenly shared in the bond.  Electrons spend more time around one of the elements.

How to show a bond is polar  means a partially positive charge  means a partially negative charge The Cl pulls harder on the electrons The electrons spend more time near the Cl HCl 

Polar Bond - Nonpolar Molecules Sometimes the bonds within a molecule are polar and yet the molecule is non-polar because its shape is symmetrical. H H HHC Draw Lewis dot first and see if equal on all sides

Polar Bond - NonPolar Molecule O C O

Polar Bond - Polar Molecules Not equal sharing on all sides –Polar bond between atoms –asymmetrical shape of molecule

HCl -- ++ Polar Bond - Polar Molecule Unequal Sharing

Cl H Space filling model “Electron-Cloud” model -- ++

HH O -- ++ Asymmetrical ++ Polar Bond - Polar Molecule

Water is a bent molecule O H H HH

Is it polar? HF H 2 O CCl 4 CO 2 yes no

METALLIC BOND All the atoms in a metal share all their valance electrons between them. The positive ions form a lattice surrounded by mobile electrons. A “sea” of electrons

Metallic Bond

Metals Form Alloys Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal. Examples are steel, brass, bronze and pewter.

Malleable

Electrons allow atoms to slide by.

Intermolecular Forces What holds molecules to each other

Dipole Interactions Occur when polar molecules are attracted to each other. Opposites attract but not completely hooked. HFHF  HFHF 

Hydrogen bonding Are the attractive force caused by hydrogen bonded to F, O, or N. F, O, and N make a very strong dipole. The hydrogen partially shares with the lone pair in the molecule next to it. The strongest of the intermolecular forces.

Hydrogen “Bonding” Strong polar attraction Occurs ONLY between H of one molecule and N, O, F of another H “bond”

H is shared between 2 atoms of OXYGEN or 2 atoms of NITROGEN or 2 atoms of FLUORINE Of 2 different molecules