Electrons and Chemical Bonding Chemical bonding is the joining of atoms to form new compounds. The attractive force that holds elements together is called the chemical bond. The outer-most electrons in an atom are key to bonding. – The electrons in the outer energy level are called valence electrons. These electrons become important when an atom bonds to another atom.

Valence Electrons The number of valence electrons can be determined from the periodic table. Groups 1 and 2 have the same number of valence electrons as their group number. Groups 3-12 do not follow a certain rule. Groups have 10 less valence electrons than their group number.

Ionic and Covalent Bonding Atoms bond when their valence electrons interact. Octet Rule – Atoms bond in order to fill their outer most energy level with eight electrons. Hydrogen and Helium are the only exception they need two electrons to fill their outer most energy levels.

Ionic and Covalent Bonding Why do the noble gases not react with anything? Why does helium not react with anything?

Ionic Bonding Ionic bonds are formed by the attraction between oppositely charged ions. One atom gains electrons and forms an anion, while the other atom loses electrons and forms a cation. What do opposites changes do? – They attract each other. One example of an ionic compound is salt. Na transfers an electron to Cl. Na forms a +1 cation, while Cl gains and electron and forms a –1 anion. The oppositely charged ions attract each other and form sodium chloride (salt).

Each +1 Na cation attracts several –1 Cl anions, and each –1 Cl anions attracts more +1 Na cations. This goes on and on to form a tight networks of ionic bonds. This is why ionic compounds form crystal- like structures that have high melting points. The simplest ratio of ions in an ionic compound is called the formula unit. The chemical formula tells us the formula unit of an ionic compound.

The formula unit for salt is NaCl. This means that there is one Na cation for every one Cl anion.formula unit

As solids ionic compounds do not conduct electricity, because their ions are locked into place. However when dissolved or melted their ions are free to move and therefore can conduct electricity. Ionic compounds tend to be brittle and break apart when hit with a hammer.

Electron Dot Diagrams Electron dot diagrams (Lewis Structures) are used to show the transfer or sharing of electrons when bonds are formed. Lewis Dot structures use dots around the element’s chemical symbol to represent the atoms valence electrons. For example the Lewis dot structure for hydrogen look like this. H

Electron Dot Structures Draw the Lewis dot structures for Na, N, O, and Cl.

Lewis structures are used to show the transfer of electrons to form ionic bonds. The following example shows the transfer of electrons from an Na atom to a Cl atom to form NaCl (salt). Draw Dot structure and show transfer of electrons (2 points) Write out ions formed (1 point) Write Chemical Formula (1 point)

Use Lewis structures to show the transfer of electrons between Ca and F to form CaF 2.

Use Lewis structures to show the transfer of electrons between K and O.

Covalent Bonding Covalent bonds are formed when atoms share one or more pairs of electrons. Covalently bonded atoms are made up of molecules, which is a neutral group of atoms held together by covalent bonds. Most covalent compounds have low melting points and do not conduct electricity when dissolved in water or melted.

Covalent compounds are formed when nonmetals bond with other nonmetals. – The atoms are forced to share electrons, because each of the atoms has several valence electrons Atoms may share more than one pair of electrons. – A double bond is formed when two atoms share two pairs of electrons or four electrons. – A triple bond is formed when atoms share three pairs of electrons or six electrons.

Lewis structures can also show the sharing of electrons in covalent bonds Bars are used to show the shared pair of electrons in a covalent bond. Use Lewis structures to show how two Cl atoms for a single covalent bond. Draw dot structure and use Venn diagrams to show sharing of electrons (2 points) Draw Structural Formula (1 point)

Use Lewis structures to show how two O atoms form a double bond.

Polar and Non-polar Bonds Tug of war with shared pair of electrons – Polar is an unequal sharing – Non-polar is an equal sharing Electrons spend more time with the more electronegative element.

Polarity Depends on Shape

Intermolecular Attractions Van der Waals Forces – Dipole interactions – polar molecules attach to each other – Dispersion forces – moving electrons momentarily create dipoles in non-polar molecules Explains why bromine is liquid at room temp.

Hydrogen Bonds Covalent bond between H and strongly electronegative N, F, and O is strongly polar.

Molecular Properties Physical properties like melting and boiling point depend on the type of bond

Network Structures

Chemical Bonding

Monatomic Ions Cations – Group 1A, 2A, and 3A form + ions with charge = to group number Anions – Group A anions charge is determined by subtracting 8 from group number

Ions of Transition Metals

Polyatomic Ions Covalent compound that have lost or gained electrons Contains both types of bonds Ones ending in –ate have one more oxygen than those ending in –ite Ions beginning with H have a charge that is one less than their counterpart.

Polyatomic ions NameFormulaNameFomula AcetateCH 3 CO 2 - HydroxideOH - CarbonateCO 3 2- HypochloriteClO - ChlorateClO 3 - NitrateNO 3 - ChloriteClO 2 - NitriteNO 2 - CyanideCN - PhosphatePO 4 3- Hydrogen Carbonate HCO 3 - PhosphitePO 3 3- Hydrogen SulfateHSO 4 - SulfateSO 4 2- Hydrogen SulfiteHSO 3 - SulfiteSO 3 2- AmmoniumNH 4 +

Polyatomic Ions

Naming Binary Ionic Compounds Binary means the compound is composed of two elements Most ionic compounds contain a metal and a nonmetal ion Place cation ion name first followed by the anion name. Be sure to include Roman numerals to show charge of transition metal

Naming ionic compounds Two part naming system Name the first element – If first element is not a transition metal, name the second element and change the ending to -ide. – If first element is a transition metal, determine the charge and use Roman numerals in parentheses to show the charge of the ion. Then change the ending to -ide.

Oxidation Numbers An oxidation number is a positive or negative number assigned to an atom to indicate its degree of oxidation or reduction. It can be helpful in determining what roman numeral to use in the stock naming system for transition metals What is the oxidation number of each kind of atom in the following compounds : a. CuBr 2 b. FeOc. PbCl 2 d. Fe 2 O 3

Examples Name the following examples: – BaF 2 – NaF – AlCl 3 – CaCl 2 Determine the charge of a transition metal cation and name the following compounds. – FeO – Fe 2 O 3 – CrO

Writing Formulas Try to write the formulas for the following examples. – Aluminum fluoride – Lithium oxide – Cobalt (III) hydroxide

Polyatomic ions NameFormulaNameFomula AcetateCH 3 CO 2 - HydroxideOH - CarbonateCO 3 2- HypochloriteClO - ChlorateClO 3 - NitrateNO 3 - ChloriteClO 2 - NitriteNO 2 - CyanideCN - PhosphatePO 4 3- Hydrogen Carbonate HCO 3 - PhosphitePO 3 3- Hydrogen SulfateHSO 4 - SulfateSO 4 2- Hydrogen SulfiteHSO 3 - SulfiteSO 3 2- AmmoniumNH 4 + PermanganateMnO 4 -

Naming Compounds with Polyatomic Ions Name the cation first then the anion NH 4 + (Ammonium) is the only positive polyatomic ion Name the following compounds – Al(OH) 3 – NaHCO 3 – Ca(CN) 2 – Ba 3 (PO 4 ) 2

Naming Molecular Compounds Numerical prefixes are used to name the elements in a covalent compound In a two-element covalent compound the elements are named from left to right on the periodic table. If there is only one first element, no prefix is used. Otherwise the following prefixes are used for all the elements with more than one atom in the compound. Always change the ending of the second element to –ide.

Examples Name the following covalent compounds using the prefixes to the left. – SiO 2 – CO 2 – N 2 O 4 – BF 3

Hydrates Follow form: AZ *XH 2 O – AZ is the formula unit – X is number of water molecules trapped in the crystal Use numerical prefixes to tell the number of water molecules trapped in the crystal

Naming Acids Acids produce H + ions when dissolved in water Follow form H n X – X is a monatomic or polyatomic anion – n indicates the number of H + ions – If X ends in –ide change prefix to hydro- and suffix to –ic – If X ends in –ite the acid name is the stem of the anion with suffix –ous followed by the acid – If X ends in –ate the acid name is the stem of the anion with suffix –ic followed by the acid

Naming Bases A base produces hydroxide ions when dissolved in water Bases are named in the same way as other ionic compounds

Examples Write the name of the following acids and bases – HNO 2 – LiOH – HMnO 4 – Al(OH) 3 – HClO 4

Metallic Bonds Valence electrons are able to move between atoms like a sea of electrons. – Conduct electricity – Malleable – Ductile

Metallic Bonds

Crystalline Structure of Metals

Alloys An alloys is a mixture of two or more elements in which at least one is a metal. – Brass – copper and zinc – Bronze – copper and tin – Cast iron – iron and carbon – Stainless steel – iron, chromium, carbon, and nickel