UNIT 5.1 Types of bonds
REVIEW OF VALENCE ELECTRONS Valence electrons are electrons in the outmost shell (energy level). They are the electrons available for bonding.
Group 1 (alkali metals) have 1 valence electron
Group 2 (alkaline earth metals) have 2 valence electrons
Group 13 elements have 3 valence electrons
Group 14 elements have 4 valence electrons
Group 15 elements have 5 valence electrons
Group 16 elements have 6 valence electrons
Group 17 (halogens) have 7 valence electrons
Group 18 (Noble gases) have 8 valence electrons, except helium, which has only 2
Transition metals ( d block) have 1 or 2 valence electrons
Lanthanides and actinides ( f block) have 1 or 2 valence electrons
DOT NOTATIONS An atom s valence electrons can be represented by Lewis dot notations. 1 valence e - 2 valence e - 3 valence e - 4 valence e - X X X X 5 valence e - 6 valence e - 7 valence e - 8 valence e - X X X X
DOT NOTATIONS PERIOD 2 Lewis dot notations for the valence electrons of the elements of Period 2. lithium beryllium boron carbon Li Be B C nitrogen oxygen fluorine neon N O F Ne
BONDING Atoms seldom exist as independent particles. They usually combine with other atoms to form compounds A chemical bond hold atoms together Electrical attraction between the nuclei and valence electrons of atoms Bonds will form if the compound is more stable than the individual atoms (potential energy decreases)
ELECTRONEGATIVITY In a chemical bond, one atom will pull on the electrons more than the other one Electronegativity measure the ability of an atom to attract electrons in a compound Fluorine has the highest electronegativity value = 4.0 The closer an atom is to fluorine the higher its electronegativity (the more pull it has on electrons)
TYPES OF BONDS Metallic (metals): attraction of nuclei to sea of electrons Ionic (metal/nonmetal): transfer of electrons to form ions- big electroneg. difference so one atom is strong enough to take an electron Covalent (2 nonmetals): share electrons- small electroneg. difference so one atom isn t strong enough to take an electron so instead they share electrons Remember the most stable configuration is when atoms have 8 electrons in their highest shell (octet rule) except Hydrogen and Helium
PRACTICE Label as ionic, covalent, or metallic bonding A. NaF B. CaBr 2 C. H 2 S D. Al 2 O 3 E. Cu A. ionic B. ionic C. covalent D. ionic E. metallic F. covalent F. NO 3
METALLIC BONDING Strong forces of attraction are responsible for the high melting point of most metals.
METALLIC BONDING The chemical bonding that results from the attraction between metal cations and the surrounding sea of electrons Vacant p and d orbitals in metal's outer energy levels overlap, and allow outer electrons to move freely throughout the metal Valence electrons do not belong to any one atom (sea of e - or delocalized e - or mobile e - )
Metals are bonded to themselves with metallic bonding Fe, Cu, Na You ll also see metallic bonding in alloys
METAL ALLOYS
PROPERTIES OF METALS Metals are good conductors of heat and electricity. Any substance can conduct electricity if there are charged particles that are free to move around
PROPERTIES OF METALS Metals are malleable Metals are ductile Metals have luster High melting and boiling points The higher the melting or boiling point-the stronger the bond because the bond needs to be broken to melt or boil These properties are all due to the mobile electrons
UNIT 5.2 Ionic bonding
CLASS STARTER 1. Label as ionic, covalent, or metallic a. CO 2 b. MgBr 2 c. H 2 O d. Fe e. AlN 2. Why do metals conduct electricity? 3. Find the charge of each as an ion a. N b. Ba c. O d. Al
IONIC BONDING
THE OCTET RULE IONIC COMPOUNDS Ionic compounds form so that each atom, by gaining or losing electrons, has an octet of electrons in its highest occupied energy level. Metals lose electrons to form positively-charged cations Nonmetals gains electrons to form negativelycharged anions
IONIC BONDING: THE FORMATION OF SODIUM CHLORIDE Sodium has 1 valence electron Chlorine has 7 valence electrons An electron transferred gives each an octet Na: 1s 2 2s 2 2p 6 3s 1 Cl: 1s 2 2s 2 2p 6 3s 2 3p 5
IONIC BONDING: THE FORMATION OF SODIUM CHLORIDE This transfer forms ions, each with an octet: Na + 1s 2 2s 2 2p 6 Cl - 1s 2 2s 2 2p 6 3s 2 3p 6
IONIC BONDING: THE FORMATION OF SODIUM CHLORIDE The resulting ions come together due to electrostatic attraction (opposites attract): Na + Cl - The net charge on the compound must equal zero
Metal Monatomic Cations Ion name Lithium Li + Lithium Sodium Na + Sodium Potassium K + Potassium Magnesium Mg 2+ Magnesium Calcium Ca 2+ Calcium Barium Ba 2+ Barium Aluminum Al 3+ Aluminum
Nonmetal Monatomic Anions Ion Name Fluorine F - Fluoride Chlorine Cl - Chloride Bromine Br - Bromide Iodine I - Iodide Oxygen O 2- Oxide Sulfur S 2- Sulfide Nitrogen N 3- Nitride Phosphorus P 3- Phosphide
IONIC COMPOUNDS Compounds are always neutral Formula units show the smallest whole number ratio of atoms so that the charges balance out. Even though ions are formed, we do not show the charges because they balance out. Calcium + fluorine Ca 2+ and F - CaF 2
EXAMPLES OF IONIC COMPOUNDS MgCl 2 Na 2 O Al 2 S 3 Magnesium chloride: Magnesium loses two electrons and each chlorine gains one electron Sodium oxide: Each sodium loses one electron and the oxygen gains two electrons Aluminum sulfide: Each aluminum loses two electrons (six total) and each sulfur gains two electrons (six total)
PRACTICE Write the formula for each Strontium and oxygen Aluminum and chlorine Cesium and sulfur Aluminum and nitrogen Aluminum and oxygen Barium and oxygen Silver and phosphorus Calcium and chlorine Aluminum bromine SrO AlCl 3 Cs 2 S AlN Al 2 O 3 BaO Ag 3 P CaCl 2 AlBr 3
IONIC COMPOUNDS The formula for ionic compounds does not show the exact number of atoms that are bonded together. A lattice or network of ions are formed and the formula tells the smallest whole number ratio of atoms that bond.
SODIUM CHLORIDE CRYSTAL LATTICE Ionic compounds form solid crystals at ordinary temperatures. Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions. All salts are ionic compounds and form crystals.
PROPERTIES OF IONIC COMPOUNDS Structure: Crystalline solids (brittle) Melting point: Generally high Boiling Point: Electrical Conductivity: Solubility in water: Generally high Excellent conductors, molten and aqueous Generally soluble
COVALENT BONDING Unit 5.3
CLASS STARTER 1. List two properties of ionic compounds 2. Which of the following will conduct electricity a. Solid Mg b. solid NaF c. liquid NaF 3. Write the formula when the following bond a. Magnesium + oxide b. sodium + nitride c. Aluminum + cyanide d. zinc + nitrite 4. Which of the following are salts? a. Solid Mg b. CO 2 c. KCl
THE OCTET RULE AND COVALENT COMPOUNDS Covalent compounds tend to form so that each atom, by sharing electrons, has an octet of electrons in its highest occupied energy level. Covalent compounds involve atoms of nonmetals only. The term molecule is used exclusively for covalent bonding
MOLECULES Molecules are neutral groups of atoms held together by covalent bonds. A molecular formula tells the exact number of atoms in the molecule CH 4 has exactly 1 carbon atom bonded to 4 hydrogen atoms H 2 O has exactly 2 hydrogen atoms and 1 oxygen atom
COVALENT BONDING Bonding models for methane, CH 4. Models are NOT reality. Each has its own strengths and limitations.
PROPERTIES OF MOLECULAR COMPOUNDS Nonconductors (no ions) Low melting and boiling points ( Usually gases at room temperatures) This is because when melting or boiling, the covalent bond doesn t break, the molecules are pulled apart (not the atoms) and molecules are held together with weak attractions. It s very easy to pull molecules apart and therefore they are usually gases
DIATOMIC ELEMENTS Some elements will naturally bond to themselves to form a molecule in elemental form Hydrogen, nitrogen, fluorine, oxygen, iodine, chlorine, bromine (have no fear of ice clear beer) H 2, N 2, F 2, O 2, I 2, Cl 2, Br 2
THE OCTET RULE: THE DIATOMIC FLUORINE MOLECULE F F 1s 2s 2p Each has seven valence electrons 1s 2s 2p F F
THE OCTET RULE: THE DIATOMIC OXYGEN MOLECULE O O 1s 2s 2p Each has six valence electrons 1s 2s 2p O O
THE OCTET RULE: THE DIATOMIC NITROGEN MOLECULE N N 1s 2s 2p Each has five valence electrons 1s 2s 2p N N
COVALENT BONDS Bond length is the distance between atoms (potential energy is low) Bond energy is the energy needed to break the bond. Shorter bonds have higher bond energy (stronger)
An indication of bond strength and bond length Single bond: 1 pair of e- shared Ex: F 2 :F-F: Double bond: 2 pairs of e- shared Longest, weakest Ex: O 2 O=O Triple bond: 3 pairs of e- shared Ex: N 2 :N N: Shortest, strongest 51
POLARITY Covalent bonds can either be polar or nonpolar. nonpolar; the hydrogens share the electrons equally H 2 HF polar: fluorine pulls the electrons closer so they share the electrons unequally In a polar molecule, one end is partially positive and one is partially negative (Dipole) s + s - + H F or H F (vector points to neg. end) 52