CHEMICAL BONDS An Element’s Search for Happiness (chemical stability)

CHEMICAL BONDS The forces that hold atoms together…often driven by the Octet Rule and stability. (Mutual electrical attraction between nuclei and valence electrons of different atoms that binds them.)

Chemical Bonds The negatively charged electrons determine how two or more atoms will interact when they are brought near each other. In a sense, the atoms fight over the available electrons

Octet Rule Atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. 8 (most of the time) 2 (1 st energy level) or Happy dogs!

IONIC BONDS One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog stealing the other dog's bone. One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog stealing the other dog's bone.

IONIC BONDS Chemical bonding that results from transfer of electrons and electrical attraction between cations and anions. Form between metals (on the left side of the Periodic Table) and non-metals (on the right side of Periodic Table) Form between metals (on the left side of the Periodic Table) and non-metals (on the right side of Periodic Table) Metal loses electron(s) and becomes positively charged…a cation. Metal loses electron(s) and becomes positively charged…a cation. Non-metal gains electron(s) and becomes negatively charged…an anion. Non-metal gains electron(s) and becomes negatively charged…an anion. The oppositely charged ions are held together because they are strongly attracted to each other. The oppositely charged ions are held together because they are strongly attracted to each other. Determine difference in electronegativity Determine difference in electronegativity –See page 429 –Difference of greater than 1.7 is often considered ionic –Ionic character greater than 50%

IONIC BOND? Cs and F? Cs and F? Page 429 electronegativity chart Page 429 electronegativity chart F en = 4.0 Cs en = is the electronegativity difference 3.3 is the electronegativity difference  A bond between Cs and F is ionic, greater than 1.7

IONIC COMPOUNDS Expressed as “formula units” rather than molecules because they form networks of ions attracted to each other…not independent neutral units. Expressed as “formula units” rather than molecules because they form networks of ions attracted to each other…not independent neutral units. Characteristics: Characteristics: –Crystalline structure –High melting points –Brittle –Dissolve in water –This separates the ions by breaking the ionic bonds…separated ions move freely making solution of ionic compounds good conductors of electricity. –Also conductive when melted.

Formula unit is NaCl, 1 sodium and 1 choride, the simplest ratio Ionic compounds form orderly arrangements of the ions, called crystal lattices.

COVALENT BONDS Bonds formed when electrons are shared   Covalent bonds form between non-metals (on the right side of the Periodic Table)   The electrons are shared by the atoms.   Electrons may be shared equally or unequally.   Molecules are formed because atoms sharing electrons must be near each other

COVALENT BONDS  Enormous variety of size, shape, physical, and chemical properties.  often lower melting point,  not necessarily crystalline  do not conduct electricity,  may or may not dissolve in water

COVALENT BONDS The dogs share the bones. There are two types of sharing: UNEQUAL EQUAL

POLAR COVALENT BONDS  In a covalent bond, the electrons are shared between atoms to fulfill the Octet Rule for both.  In a polar covalent bond, the electrons are shared unequally. They are attracted more to the more electronegative element.  The electrons spend more time near the more electronegative element, making it seem more negative and the other end of the molecule seem more positive…or “polar” Determine difference in electronegativity Determine difference in electronegativity –See page 429 –Difference of is often considered polar covalent…but different sources give different ranges –Ionic character 5-50%

POLAR COVALENT BONDS Unevenly matched dogs that are willing to share. These bonds can be thought of as two or more dogs that have different desire for bones. They share unequally.

POLAR COVALENT BOND? Unequal sharing of electrons Unequal sharing of electrons Partial negative charge Partial positive charge

POLAR COVALENT BOND? H and S? H and S? Page 429 Page 429 S en = 2.5 H en = is the electronegativity difference 0.4 is the electronegativity difference  A bond between H and S is polar covalent,.3-1.7

Polar molecules and polar bonds Partial positive charge towards less electronegative element Partial negative charge towards element with greater electronegativity. Two sides to the molecules/bonds S

Polar bonds lead to polar molecules

Polamolecules Polamolecules Calm, quiet, humble on the sideline Fearless, crazed, maniacal on the field Two sides to Troy Polamalu

Polar molecules and polar bonds Partial positive charge towards less electronegative element Partial negative charge towards element with greater electronegativity. Two sides to the molecules/bonds S

NON-POLAR COVALENT BONDS  In a covalent bond, the electrons are shared between atoms to fulfill the Octet Rule for both.  In a non-polar covalent bond, the electrons are shared equally.  The charge is evenly distributed between both atoms. The molecule is non-polar meaning one side does not have more charge than the other. Determine difference in electronegativity Determine difference in electronegativity –See page 429 –Difference of less than.3 is often considered nonpolar covalent…again some sources give different range –Ionic character less than 5 %

NON-POLAR COVALENT BONDS Covalent Bonds: Dogs of equal strength share equally. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones. Covalent Bonds: Dogs of equal strength share equally. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones. They share equally.

NON-POLAR COVALENT BOND? Cl and Br? Cl and Br? Page 429 for en Page 429 for en Cl en = 3.0 Br en = is the electronegativity difference 0.2 is the electronegativity difference  A bond between Cl and Br is non=polar covalent, less than 0.3

NON-POLAR COVALENT BOND? Equal sharing of electrons Equal sharing of electrons Equal distribution of charge Equal distribution of charge

Diatomic Elements They pair up! Br 2 Br 2 I 2 I 2 N 2 N 2 Cl 2 Cl 2 H 2 H 2 O 2 O 2 F 2 F 2 The diabolical DIATOMIC BrINClHOF TWINS!

METALLIC BONDs  Electrons are “delocalized”  Electrons move freely around and between atoms in the network of empty orbitals. The electrons move through the substance with little restriction. The model is often described as the "kernels of atoms in a sea of electrons.”

METALLIC BONDS  The free movement of electrons explains the properties of metals…  Conductivity: free movement of electrons  Malleability & ductility: bonding is the same in all directions  Luster: energy released as electrons move easily between orbitals

METALLIC BONDS Mellow dogs with plenty of bones to go around. They don’t have to worry about sharing!

We will look more closely at the different types of bonds to understand how millions of different compounds form from only about 100 different elements!

Lewis Dot of Ionic Compounds (electrons taken, not shared) Write the dot structures of the neutral atoms Write the dot structures of the neutral atoms Write the ions created by the loss or gain of electrons, in brackets. The metals have no dots. The non-metals have a full outer shell. Write the ions created by the loss or gain of electrons, in brackets. The metals have no dots. The non-metals have a full outer shell. Show the ion charges as superscripts. Show the ion charges as superscripts. Show the ratio of ions needed to create a net charge of zero as a subscript. Show the ratio of ions needed to create a net charge of zero as a subscript.

Criss-Cross Method to Determine Ratio of Ions Write the ion symbols and charges (superscripts). Get this info from periodic table for elements, polyatomic ion list for polyatomic ions. Write the ion symbols and charges (superscripts). Get this info from periodic table for elements, polyatomic ion list for polyatomic ions. Criss-cross the charge (numbers only) to subscripts. This shows the ratio of ions required for a net charge of zero. Criss-cross the charge (numbers only) to subscripts. This shows the ratio of ions required for a net charge of zero. Simplify. Mg 2+ N 3- Simplify. Mg 2+ N 3- Mg 3 N 2

Charges of ions from PT group ve or 8 charge /

Why does it work? The goal is a net charge of 0. The charges, or oxidation numbers, must add up to zero. Mg 3 N 2 3 x 2 + = x 3 - = net charge 0 net charge

Covalent bonds usually follow the octet rule Put all of the valence electrons in a pot and distribute them between the atoms so each atom has a full octet by sharing up to 3 pairs of electrons. Put all of the valence electrons in a pot and distribute them between the atoms so each atom has a full octet by sharing up to 3 pairs of electrons. : single bond :: double bond :: triple bond

Lewis Dot Structures of Covalent Bonds(shared electrons) Lewis dot structures show atoms near each other sharing pairs of electrons to create bonds and satisfy octet rule for both atoms. Lewis dot structures show atoms near each other sharing pairs of electrons to create bonds and satisfy octet rule for both atoms. They may share up to 3 pairs of electrons They may share up to 3 pairs of electrons –1 SHARED PAIR :SINGLE BOND –2 SHARED PAIRS ::DOUBLE BOND –3SHARED PAIRS :::TRIPLE BOND It does not matter which atom the electrons come from because they are shared. It does not matter which atom the electrons come from because they are shared.

Lewis Dot Structures of Covalent Compounds Molecules are formed Molecules are formed Atoms sharing electrons stay near each other Atoms sharing electrons stay near each other Shared electrons that are involved in bonds are shown using pairs of dots : Shared electrons that are involved in bonds are shown using pairs of dots : OR pairs of dots in a bond may be replaced by single lines - a line for each shared pair of electrons OR pairs of dots in a bond may be replaced by single lines - a line for each shared pair of electrons

Nomenclature A fancy word for naming things A fancy word for naming things –Looking at a formula and giving the compound a name –Looking at a name and writing the formula USE THE FLOW CHART FOR THE HOMEWORK EVERY TIME USE THE FLOW CHART FOR THE HOMEWORK EVERY TIME –By the time you have finished the packet, you will understand the system IF you THINK about what you are doing and use the flow chart

Binary compounds 2 elements 2 elements Where are they on PT? Where are they on PT? –Metal and non-metal: ionic  Name the metal  Name the non-metal with an –ide ending  Include a Roman numeral to show the charge of the metal if it is a transition metal (exceptions,Ag, Cd, Zn do NOT need Roman numeral and Sn, Sb, and Pb DO need a Roman numeral

Binary compounds 2 elements 2 elements Where are they on PT? Where are they on PT? –Non-metal and non-metal: Covalent  Name the first element using prefix only if there is more than 1  Name the second element with a prefix and an –ide ending Mono,di,tri,tetra,penta,hexa,hepta,octa,nona,deca

Tertiary compounds 3 or more elements 3 or more elements Involve polyatomic ions: groups of atoms bonded covalently and moving together as a charged group, an ion made up of several covalently bonded atoms Involve polyatomic ions: groups of atoms bonded covalently and moving together as a charged group, an ion made up of several covalently bonded atoms See your list See your list They have specific formulas, names, and charges which must be memorized They have specific formulas, names, and charges which must be memorized EXAMPLES EXAMPLES –ammonium –NH 4 1+ ammonium –hydroxide –OH 1- hydroxide –sulfate –SO 4 2- sulfate

Writing formulas… reverse the process Prefixes? Prefixes? –The prefixes tell you the number of each element –Elements written in order –No Criss-cross

No prefixes…ionic What is the ending? What is the ending? –-ide? Usually binary (exceptions ammonium and hydroxide)  Write the symbol and charge of each element or ion –Charges of transition elements are the Roman numerals –Charges of others are from PT  Criss-cross charge numbers to determine subscripts which will yield net charge of zero. (Reduce, assume “ones”)

No prefixes…ionic What is the ending? What is the ending? –-ite or –ate –Polyatomic –Find the polyatomic ions and elements –Write symbols and charges of each –Criss-cross

Acids If hydrogen is the cation, the substance is an acid If hydrogen is the cation, the substance is an acid If the anion ends in –ide If the anion ends in –ide –Hydro+name of anion with –ic ending+ acid If the anion ends in –ate If the anion ends in –ate –Name anion with –ic ending+ acid If the anion ends in –ite If the anion ends in –ite –Name the anion with –ous ending+ acid –Reverse rules for formula writing

Hydrates Some compounds absorb water in a specific ration into the crystal structure Some compounds absorb water in a specific ration into the crystal structure Name the compound following the rules Name the compound following the rules Add a big dot Add a big dot Use a prefix in front of the word hydrate to show how many water molecules Use a prefix in front of the word hydrate to show how many water molecules Reverse rules for formula writing Reverse rules for formula writing