Ionic Bonds and Ions Chemical Bonding A Chemical Bond is the force of attraction that holds two atoms together as a result of the rearrangement of electrons between them. When atoms bond, electrons may be transferred from one atom to another, or they may be shared between the atoms. The change results in a Chemical Reaction Ionic Bonding Ionic Bonds = valence electrons are transferred from one atom to another to make both atoms more stable. Atoms want to reach a stable 8 valence electrons • Atoms with 5, 6, or 7 valence electrons usually become more stable when this number increases to 8. • Atoms with 1, 2, or 3 valence electrons become more stable when they lose electrons Valence Electron Review • Where on the periodic table do you find atoms with 5,6, 7 valence electrons and atoms with 1, 2, 3? Ions • An ION is an atom that has gained or lost an electron, giving it an electrical charge. – The addition of electrons to an atom creates a negatively (-) charged atom – The loss of electrons from an atom creates positively (+) charged ions Atoms will gain or lose electrons to reach a stable 8 valence electrons. (VIDEO) Forming Ionic Compounds • When ionic bonds form, the opposite charges of the ions cause the ions to stick together. But the compound formed is neutral because the charges cancel each other. • Li (1+) + Cl (1-) LiCl (neutral) • When a metal and a nonmetal combine by ionic bonding, the resulting compound has different properties than the metal and nonmetal did. • Ionic compounds are brittle and highly soluble, with high melting and boiling points. Examples Sodium has 1 valence electron that it wants to lose to become stable: Chlorine has 7 valence electrons and it wants 1 more to become stable: When Sodium’s valence electron is transferred to Chlorine, both elements become ions. Because Sodium loses an electron it becomes a positive (+) ion. Because Chlorine gains an electron it becomes a negative (-) ion. The two atoms bond to form: + - Examine Figure 4 on page 233. • Here we can see what is happening with the valence electrons. • Working with your partner, begin the ionic bonds side of the worksheet Ionic Bonding Review • Ionic bonds are bonds that form when electrons are transferred from one element to another • Ionic bonds form between metals and nonmetals • Elements in groups 1,2, 13 lose electrons and become positive ions (+ charge) • Elements in group 15, 16 , 17 gain electrons and become negative ions (- charge) • The ionic compound has no charge Steps for forming Ionic Bonds 1. Identify the two elements that will bond 2. Figure out which will give and which will take valence electrons 3. Figure out which element is the positive and which is the negative ion 4. Calculate the number of each element you need 5. Write the compound name: The positive ion goes first, then the negative Step 1: Identify Elements Lithium and Bromine Step 2: Atoms do what is easiest • When deciding whether an element will gain or lose valence electrons in an ionic bond, go with the smaller number: 1. Lithium has 1 valence electron, it needs 7 – what will it do? 2. Bromine has 7 valence electrons, it needs 1 So when these two elements bond Li will give its 1 electron to Br Atoms do what is easiest • When deciding whether an element will gain or lose valence electrons in an ionic bond, go with the smaller number: 1. Sodium has 1 valence electron, it needs 7 – what will it do? 2. Sulfur has 6 valence electrons, it needs 2, what will it do? 3. Bromine has 7 valence electrons, it needs 1 4. Aluminum has 3 and needs 5 Step 3: Ions Since Li is giving away its electron it has more protons (+) than electrons (-). Since Br is taking an electron it has more electrons (-) than protons (+) Li is the positive ion, Br is the negative ion (if it gains weight (electrons) it is sad (negative), if it loses it is happy (positive) Charges of Ions • Since atoms do what is easiest, it is easy to figure out the charge on an ion: 1. B loses 3 electrons, so the charge is _______ 2. S gains 2 electrons, so the charge is _______ 3. Cl gains 1 electron, so the charge is _______ 4. What about As, K, Ca? Step 4: How many of each? Since Li has one to give away and Br only needs one the ratio of elements in this compound is 1:1 Step 5: Write out the compound The positive ion goes first, the negative ion goes second: LiBr (Lithium Bromide) Naming Ionic Compounds 1. Always put the positive ion (metal) name first 2. The name of the negative ion that is formed in the compound usually changes to end with –ide. EXAMPLE: Sodium Chloride • The ions that make up an ionic compound are bonded in a repeating three-dimensional pattern called a crystal lattice. Ionic Compound Diagrams You can draw the electron dot diagrams for ionic compounds • To draw ionic compound diagrams: 1. draw the compound formula 2. Draw the charges of the ions (number & sign)* 3. Draw the 8 valence electrons around them *Draw the charge = the number given or taken and the + or – sign (2+, 2-, 3+ etc) Examples Sodium has 1 valence electron that it wants to lose to become stable: Chlorine has 7 valence electrons and it wants 1 more to become stable: When Sodium’s valence electron is transferred to Chlorine, both elements become ions. Because Sodium loses an electron it becomes a positive (+) ion. Because Chlorine gains an electron it becomes a negative (-) ion. The two atoms bond to form: + - Elements do not always have to have the exact number of electrons to give and take in order bond. But you must use more of them in order to form the correct amount of valence electrons: • Because Sodium only has 1 electron, it wants to lose 1 and becomes a positive (+) ion. • Because Oxygen has 6 valence electrons, it wants to gain 2, to become a negative (-) ion. • In order to form a bond, you need 2 Sodiums for every 1 Oxygen: • When drawing ionic compounds – REMEMBER: - The positive ion goes on the left, the negative ion goes on the right - Always write the number and charges above the chemical symbol - Don’t forget the subscript if it has one! - The number of electron dots is always 8 Draw the electron dot diagram and charges for the compounds: 1. Magnesium Sulfide 2. Potassium Chloride 5. Aluminum Chloride 3. Magnesium Oxide 4. Calcium Oxide Ending Questions 1. 2. 3. 4. 5. 6. 7. 8. What is an ionic bond? What category of elements form ionic bonds? What is an ion? How do ions form? How many valence electrons does sodium have? Will Sodium gain or lose electrons? How about Magnesium, Oxygen? When atoms gain electrons, what charge do they have? 9. When atoms lose electrons, what charge do they have? Exit Tickets • Complete the exit ticket and turn in to Ms. Gorence in order to be dismissed today!