Determine the number of valence electrons in an atom of a representative element Explain how the octet rule applies to atoms of metallic and non-metellic elements Describe how cations and anions form Responsible for the chemical properties of atoms and are those in the outer energy level Valence electrons the s and p electrons in the outer energy level The highest occupied energy level Core electrons electrons in the energy levels below highest levels Atoms in the same column... 1) Have the same outer electron configuration. 2) Have the same valence electrons. The number of valence electrons are easily determined. It is the group number for a representative element Group 2A: Be, Mg, Ca, etc. have 2 valence electrons Usually only electrons used in chemical bonds!!! This means that only valence electrons are shown in electron dot structures To us older generations formerly known as Lewis Dot Diagrams A way of showing & keeping track of valence electrons. How to write them? Write the symbol - it represents the nucleus and inner (core) electrons Put one dot for each valence electron ( 8 maximum ) They dont pair up until they have to X The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons to show l First we write the symbol N l Then add 1 electron at a time to each side l Now they are forced to pair up Draw the Electron Dot Diagrams of the following: Carbon Argon Calcium Aluminum Octet 8 valence electrons Associated with stability of the noble gases Exception: Helium He is stable with 2 valence electrons In 1916, Gilbert Lewis used idea of noble gases to explain why atoms form certain kinds of ions and molecules Octet Rule in forming compounds, atoms tend to achieve a noble gas configuration 8 e - in outer level Metals LOSE electrons (left side remember!?) to attain a noble gas configuration When electrons are lost the resulting ion is POSITIVE Naming the name of a cation is the same as element Example: sodium and sodium cation Lets look at configuration of Sodium to explain why metals result in cations: Na 1s 2 2s 2 2p 6 3s 1 1 valence e - Na 1s 2 2s 2 2p 6 Noble gas configuration Same as what element? Which element is bigger? Why? Although names are the same, many chemical differences Sodium metal reacts explosively with water Sodium cation is unreactive Why? Metals will have few valence electrons (usually 3 or less) More than 3 electrons lost is rare but is seen in transition metals Lets look at calcium 2 valence electrons Ca Metals will have few valence electrons Metals will lose their valence electrons Ca Metals will have few valence electrons Metals will lose their valence electrons Ca 2+ No dots are shown for the cation Name: Calcium ion Try Scandium! Lets do Silver, element #47 Predicted configuration is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 9 Actual configuration is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 4d 10 Ag = Ag 1+ (cant lose any more, charges of 3+ or greater are uncommon) Silver cannot lose any more electrons so it does not achieve a true noble gas configuration Instead it is called pseudo-noble gas configuration Some transition metals have multiple possible oxidation states (charges). To name them, you add a ROMAN NUMERAL after the name of the element to indicate the charge: ion Non-metals gain electrons to attain noble gas configuration This results in negative charge (anion) Sulfur 1s 2 2s 2 2p 6 3s 2 3p 4 6 valence electrons S s 2 2s 2 2p 6 3s 2 3p 6 Noble gas configuration Name of an anion is usually the name of the element but you drop last syllable and add ide Chlorine anions chloride anions Oxygen anions oxygen anions Halide ion ion formed from a halogen element Non-metals have 5 or more valence electrons They will GAIN electrons to fill outer shell P 3- Called Phosphide ion SHOW dots! All atoms react to try and achieve a noble gas configuration Noble gases have 2 s and 6 p electrons 8 valence electrons = stable Explain the electrical charge of an ionic compound Describe three properties of ionic compounds Ionic compounds compounds composed of cations and anions Usually metal + non-metal Ionic bond electrostatic forces that hold ions together in ionic compounds Opposite charges are attracted to each other Transfer of electrons Metal cation first then non-metal anion with ide ending NaCl LiF In these ionic compounds there is one sodium atom for every chlorine atom Sometimes an ionic compound will have numbers in addition to symbols Magnesium chloride = MgCl 2 Chemical formula shows kinds and numbers of atoms in smallest representative unit of a substance NaCl Formula unit the lowest whole- number ratio of ions in an ionic compound MgCl 2 AlBr 3 H 2 O 2 C 6 H 12 O 6 All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable). CaP Lets do an example by combining calcium and phosphorus: CaP Ca 2+ P Ionic Bonding Ca 2+ P Ca Ionic Bonding Ca 2+ P 3- Ca Ionic Bonding Ca 2+ P 3- Ca P Ionic Bonding Ca 2+ P 3- Ca 2+ P Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca Ionic Bonding Ca 2+ P 3- Ca 2+ P 3- Ca 2+ Ionic Bonding = Ca 3 P 2 Formula Unit This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance. For an ionic compound, the smallest representative particle is called a: Formula Unit Write the formula for the ionic compound that will form between Ba 2+ and Cl - Solution: Balance charge with + and ions Write the positive ion first and negative ion second Cross charges and write number as subscripts Write the correct formula for the compounds containing the following ions: 1. Na +, S Al 3+, Cl - 3. Mg 2+, N 3- Binary ionic compounds: (what is binary?) Cation first then anion Cation = name of the element Ca 2+ = calcium ion Anion = root + ide Cl - = chloride Answer: CaCl 2 is calcium chloride Complete the names of the following binary compounds: Na 3 N KBr Al 2 O 3 MgS Transition metals (as seen before) can have more than one possible charge Roman numeral indicates charge of ion 1+ or or 3+ Cu +, Cu 2+ Fe 2+, Fe 3+ copper(I) ion iron(II) ion copper (II) ion iron(III) ion FeCl 3 (Fe 3+ ) iron (III) chloride CuCl (Cu + ) copper (I) chloride SnF 4 (Sn 4+ ) tin (IV) fluoride PbCl 2 (Pb 2+ )lead (II) chloride Fe 2 S 3 (Fe 3+ )iron (III) sulfide Complete the names of the following binary compounds with variable metal ions: FeBr 2 CuCl SnO 2 Fe 2 O 3 Hg 2 S Most ionic compounds are crystalline solids at room temperature Crystalline regular repeating arrangement of ions in solid Ions strongly bonded together Structure is rigid What does it mean to conduct electricity?? Conducting electricity means allowing charges to move In a solid (such as salt at room temp) ions are locked in place Ionic salts are insulators When melted, ions move ** Melted ionic compounds conduct electricity Model the valence electron in metal atoms Describe the arrangement of atoms in a metal Explain the importance of alloys Metals are made up of closely packed cations Metal bonds consist of attraction of free-floating valence electrons for the positively charged metal ions Forces of attraction that hold metals together Metals hold on to their valence electrons very weakly they want to give them up! Metallic bonds look like positive ions floating in a sea of electrons Electrons are free to move through the solid Metals conduct electricity Malleable hammered into shape (bend) Ductile drawn into wires These explain mobility of valence electrons - Page 201 1) Ductility2) Malleability Due to the mobility of the valence electrons, metals have: and Notice that the ionic crystal breaks due to ion repulsion! Force Mobile electrons allow atoms to slide by Force Strong Repulsion breaks a crystal apart, due to similar ions being next to each other. Force If made of one kind of atom, metal atoms are arranged in very compact and orderly patterns 3 arrangements: Body-centered cubic Face-centered cubic Hexagonal close-packed Every atom has 8 neighbors except for surface atoms Examples: Sodium Potassium Iron Every atom has 12 neighbors Examples: Copper Silver Gold Aluminum Every atom has 12 neighbors Different pattern due to hexagonal shape Examples: Magnesium Zinc Cadmium Metals are used everyday but most are not pure metals Alloys mixture of 2 or more elements (at least 1 is a metal) Made by melting a mixture of the ingredients then cooling it Example: Brass alloy of Cu and Zn Example: Bronze Cu + Sn Properties often better than pure elements Example: sterling silver is 92.5% Ag and 7.5% Cu harder and more durable than pure Ag but still soft enough to make jewelry Steel important alloy Corrosion resistant, ductile, hardness, cost Page 203 Table 7.3 Sterling silver Ag and CU Cast iron Fe and C Stainless steel Fe, Cr, C, and Ni Substitutional alloy the atoms of the components are about the same size Interstitial alloy the atomic sizes are different Smaller atoms fit into spaces of larger atoms