CHEMICAL BONDING • COVALENT BONDS • IONIC BONDS • METALLIC BONDS
Reflection (pg 62) • What is a metallic bond? • Compare/contrast it to ionic/covalent bond
Metallic Bonds • How atoms are held together in the solid. • Metals hold onto there valence electrons very weakly. • Think of them as positive ions floating in a sea of electrons.
+ + + + + + + + + + + + Sea of Electrons • Electrons are free to move through the solid. • Metals conduct electricity.
Characteristic of Metallic Bonds • High electrical and thermal conductivity • Malleable, ductile, high luster. • Great amount of heat needed to break these bonds.
When an atom of a nonmetal takes one or more electrons from an atom of a metal so both atoms end up with eight valence electrons IONIC BONDING
NONMETAL METAL SUBSCRIPTS IONIC BONDING IS THE COMPOUND AN IONIC COMPOUND? Mg N 3 2
IONIC BOND FORMATION Metal
IONIC BONDING ION – any atom with more or less electrons that it is supposed to have* *Remember that the number of electrons is supposed to be equal to the number of Protons if the atom has a neutral charge
+ + 1e - 11 p 11 e 11 p 10 e Na Na - = - - loses one electron Normal sodium atom to become sodium ion IONIC BONDING Metals will tend to lose electrons and become POSITIVE CATIONS
IONIC BONDING Na+1 is called a sodium ion The +1 symbol means it has lost one electron
+ + 1e - 17 p 17 e 17 p 18 e Cl Cl + = - - to become a chloride ion Normal chlorine atom gains an electron IONIC BONDING Nonmetals will tend to gain electrons and become NEGATIVE ANIONS
IONIC BONDING Cl-1 is called a chloride ion The -1 symbol means it has gained one electron
Properties of Ionic Compounds • Hard, brittle solids. • Strongest bond. • Most dissolve in water • Conduct electricity when dissolved in water. • High melting/ boiling points- because of strong forces between ions.
Crystalline structure The POSITIVE CATIONS stick to the NEGATIVE ANIONS, like a magnet. + + - - - - + + - + - + + - - - + +
COVALENT BOND FORMATION Non-Metal Non-Metal When one nonmetal shares one or more electrons with an atom of another nonmetal so both atoms end up with eight valence electrons
NONMETAL NONMETAL COVALENT BONDING IS THE COMPOUND A COVALENT COMPOUND? C O 2 YES since it is made of only nonmetal elements
Polar Bonds • When two different atoms are connected, the atoms may not be shared equally. • This is a polar covalent bond. pages.uoregon.edu
Nonpolar Bonds • When the atoms in a bond are the same, the electrons are shared equally. • This is a nonpolar covalent bond. 800mainstreet.com
Characteristics of Covalent Bonds • Represented by Lewis structures • Strong bond but weaker than Ionic bonds • Low melting points & boiling points • Most do not dissolve in water • Do not conduct electricity. • Usually in a gas state at room temperature
Covalent bonds • Monatomic: contains one atom • Diatomic: contains two atoms BrINClHOF Bromine (Br2), Iodine (I2), Nitrogen (N2), Chlorine (Cl2), Hydrogen (H2), Oxygen (O2), Fluorine (F2) You must have these memorized!!!! • Polyatomic: contains more than one atom.
Octet Rule Octet rule: atoms tend to gain, lose, or share electrons until they are surrounded by 8 valence electrons (4 electron pairs). Exceptions: Hydrogen forms bonds in which it is surrounded by only two electrons. Boron tends to form bonds in which it is surrounded by 6 electrons. Main group elements in period 3 and up can form bonds with expanded valance shells.
Lewis structure rules • 1.Write the element symbol. Around this draw dots—one for each valence electron. • 2. The dots sould be spread over four sides. Dots are not paired until all sides have at least one dot. • 3. It does not matter on which side dots are placed. Example- Hydrogen can be drawn in four ways: H H H H
Lewis structure rules • 4. The number of valence electrons is equal to the group number for groups 1 and 2. In groups 13 to 18, subtract 10 and that is the number of valence electrons.
Multiple bonds in Lewis Structures • Molecules containing carbon (C), nitrogen (N), and oxygen (O) may form multiple bonds. • The need for multiple bonds becomes obvious if there are not enough valence electrons to complete octets by adding unshared electron pairs.
Double bonds • Produced by sharing two pairs of electrons between two atoms. H H H H C C C C H H H H
Triple Bonds • Produced by sharing three pairs of electrons between two atoms. N
MOLECULAR SHAPES OF COVALENT COMPOUNDS
VSepR tHEORY ALENCE HELL VSEPR LECTRON AIR EPULSION
What Vsepr means Since electrons do not like each other, because of their negative charges, they orient themselves as far apart as possible, from each other. This leads to molecules having specific shapes.
Things to remember • Atoms bond to form an Octet (8 outer electrons/full outer energy level) • Do NOT forget all electron pairs, including unshared electron pairs!!!
HERE ARE THE RESULTING MOLECULAR SHAPES
Linear EXAMPLE: BeF2 • The central atom is represented by A and the atoms bonded to the central atom are B. • The molecule AB2 is linear • Bond Angle = 180°
Trigonal Planar EXAMPLE: GaF3 • The molecule AB3 makes an equilateral triangle. • Bond Angle = 120°
Tetrahedral EXAMPLE: CH4 • The molecule AB4 makes the shape of a tetrahedral (kind of looks like a pyramid). • Bond Angle = 109.5°