Ionic and Covalent bonding What holds atoms together? Ionic Bonds • A bond that holds atoms together by the attraction between oppositely charged ions • Ionic bonds are formed by the transfer of electrons • Ionic compounds form very strong bonds • Ionic compound conduct electricity when dissolved in water – Because ions are free to move Ionic bonds/compounds • Likes repel ----------opposites attract • Metal elements form cations (+ charge) • Nonmetals form anions (- charge) Always write the cation first, then the anion when writing chemical formulas Naming cations • Cation names always stay the same – Sodium, Na • Sodium ion Na+ – Calcium, Ca • Calcium ion Ca2+ Naming Anions • Anions always change from their original ending to an (ide) ending – Ex – sulfur, S • Sulfide S2- – Fluorine, F • Fluoride ion F- – Chlorine, Cl • Chloride ion Cl- Try writing the ionic names for the following elements • Bromine • Iodine • nitrogen Steps for Naming Compounds Sodium Chloride 1. List the symbols for each ion with their charge 1. Ex. Na+ Cl- 2. Put the cation first 1. Ex. Na+Cl- 3. If there is a roman numeral it is the + charge on the cation 4. Make sure that the charges (+ and -) equal an overall charge of zero 1. Ex. Na+Cl- (+1 plus -1 = 0) 5. If they don’t equal zero you must change the subscript 6. Find the lowest common multiple of the charges and divide to find new subscripts 7. Write the chemical formula Ex. NaCl Polyatomic Ions • An ion made of two or more atoms (THEY ARE COVALENT COMPOUNDS WITH A CHARGE) • You must treat them like a single unit when writing chemical formulas – Ex 2- – CO3 (Carbonate Ion) – That means that CO3 has a charge of 2- – If there are more than one polyatomic ion put them in parentheses (CO3)2 – Don’t write the charges in final answer - • NO2 – Nitrite ion – It has a negative charge – How would you write it if you had three of them? • (NO2)3 • Sulfate ion 2- – SO4 – What if you had one of them? • SO4 Practice • Rubidium Oxide – Rb2O • Calcium Chloride – CaCl2 • Potassium Sulfate – K2SO4 • Ca3N2 – Calcium Nitride • Ca3(PO4)2 – Calcium Phosphate • SrS – Strontium Sulfide • K2CO3 – Potassium Carbonate How Many Atoms? • Cu2S • FePO4 • Ca3(PO4)2 • CoCO3 • Be(OH)2 Metallic bonds • Bond formed between two or more of the metal elements • Bond formed by attraction of positive metal ions and electrons around them from other metal atoms • Metals conduct electricity when solid • Metals share electrons and they can move from one atom to the next Covalent Bonding • Formed by nonmetals • When atoms share electrons • Covalent bonds form between two or more elements above the step • When naming covalent compounds don’t worry about charges at all • All you have to know is the prefixes which tell us how many atoms there are • Video • Hydrogen •Chlorine • They can share more than one pair of electrons To name covalent copmounds • Never put mono on first element (only on second element if there is one of them) • Change ending of second element to (ide) Examples • BF3 – Boron trifluoride • N2O4 – Dinitrogen tetroxide • AsCl5 – Arsenic pentachloride • C3S8 – Tricarbon Octasulfide Try these problems • P2O5 • Na2O • Ni(CN)3 • Disilicon hexabromide • Potassium nitride – K3N Polyatomic ions • Groups of covalently bonded atoms that have lost or gained an electron.