Ions and Ionic Compounds Water Unit Section C.7

Questions To Be Answered. . . Why is the periodic table arranged the way it is? How do you make an atom happy? What does an ion look for in mate? How do they look together? Will they stay together?

Why is the periodic table arranged the way it is? “Birds of a feather flock together.” Besides being in order by the number of protons (1, 2, 3, etc.) the periodic tables is arranged so that elements with similar characteristics and properties are grouped together. (E.g. None of the noble gases like to react with other elements, and they are all in Group 8A.) One cause of many of the properties of the elements are the number of electrons

Why is the periodic table arranged the way it is? Sodium (Na) has one electron in its outermost shell. So do all the other elements in Group 1A. Na One cause of many of the properties of the elements are the number of electrons in the outer shell. One example of a property affected by this is the common ionic charge atoms of a certain element like to have. In fact, the number of the A group tells you exactly how many valence electrons an atom has. (go back to periodic chart and point out.

Practice #1 How many electrons does Magnesium have in its outer shell? 2 What about Silicon? 4 Bromine? 7 Neon? 8 - Write these down on your white board and then we’ll display them together.

Why is the periodic table arranged the way it is? Notice in a neutral atom the # of electrons = # of protons. Sodium has 11 negative charges and 11 positive charges. Na This is true for neutral atoms of all element types. The number of electrons in the outer shell can help you determine common ionic charges for many atoms as we will see when we answer our next question.

Practice #2 How many total electrons does a neutral Magnesium atom have? 12 What about Silicon? 14 Bromine? 35 Neon? 10 - Write these down on your white board and then we’ll display them together.

How do you make an atom happy? Octet rule (Rule of 8) Sodium likes to give away 1 electron to have 8 in the outer shell. Na “Atoms think its great when they have eight.” except for hydrogen and helium Atoms like to give away their electrons or steal other electrons in order to get 8 electrons in their outermost shell.

How do you make an atom happy? Sodium now has an electric charge of +1. Still 11 protons, but now only 10 electrons. 11 – 10 = +1 Na “Atoms think its great when they have eight.” Atoms like to give away their electrons or steal other electrons in order to get 8 electrons in their outermost shell.

How do you make an atom happy? Ions: Atoms with an electric charge Either gained or lost electron(s) Cation: Ion with a positive (+) charge Lost electrons Anion: Ion with a negative (-) charge Gained electrons - Atoms get an electric charge by gaining or losing electrons to get 8 in their outer shell.

How do you make an atom happy? Ions: Atoms with an electric charge Either gained or lost electron(s) Cation: Ion with a positive (+) charge Lost electrons Anion: Ion with a negative (-) charge Gained electrons - Atoms get an electric charge by gaining or losing electrons to get 8 in their outer shell.

How do you make an atom happy? Ionic charges contain 2 parts: +/- # They are written as superscripts (small & at the top) after the symbol for the atom: E.g. Na+ - 1 is not usually written

How do you make an atom happy? If an atom has < 4 electrons in its outer shell, it will give them away to become a cation. E.g. Groups 1A, 2A, & 3A If an atom has > 4 electrons in its outer shell, it will steal some more to become an anion. E.g. Groups 7A, 6A, & 5A - Like we said earlier, you can use the number of electrons in the outer shell to determine a common ionic charge for the atom, but how?

How do you make an atom happy? If an atom has 4 electrons in its outer shell, it could go either way. E.g. Group 4A If an atom already has 8 electrons in its outer shell, it does not donate or accept any electrons at all. E.g. Group 8A - Like we said earlier, you can use the number of electrons in the outer shell to determine a common ionic charge for the atom, but how?

Practice #3 How many electrons does Magnesium want to give away / steal? Donates 2 What about Silicon? Could donate or accept 4 Bromine Will accept 1 Neon? Will not donate or accept any - Write these down on your white board and then we’ll display them together.

How do you make an atom happy? The +/- of an ionic charge is determined by whether you steal or give electrons. Steal = get more negative charges = - Give = have fewer negative charges = + (Number of positively-charged protons NEVER changes) - Like we said earlier, you can use the number of electrons in the outer shell to determine a common ionic charge for the atom, but how?

How do you make an atom happy? GROUP GIVE OR TAKE COMMON CHARGE 1A Give 1 +1 2A Give 2 +2 3A Give 3 +3 4A Give or take 4 +/- 4 5A Take 3 -3 6A Take 2 -2 7A Take 1 -1 8A Neither B Varies There are exceptions to the rule, but for this class, you are not expected to know them. For Group B elements (show on periodic chart) and any other variations, their common ionic charge will be provided/supplied.

Practice #4 What is the common ionic charge for Magnesium, and how would we write the symbol for the ion? Mg+2 What about Silicon? Si+4 , Si-4 Bromine Br- Neon? Ne (not Ne0) - Write these down on your white board and then we’ll display them together.

What does an ion look for in a mate? Ions want to date other ions which have a charge opposite of their own. Cations want to form Ionic compounds with anions. E.g. Na+ & Cl- Ions also like to be equal to their mate. The positive charges of the cations should balance out the negative charges of the anions. E.g. +1 + (-1) = 0 charge

What does an ion look for in a mate? If the charges are not opposite and equal . . . E.g. Mg+2 & Cl- It may take multiple ions to balance the charge. E.g. Magnesium needs 2 Chlorines to be satisfied. E.g. +2 + 2(-1) = 0 charge - Sometimes three (or more) is company

How do they look together? “Like two peas in a pod.” - Like 2 peas in a pod

How do they look together? Always write the symbol for the cation first, followed by the anion. E.g. NaCl Write the number of each ion you need to balance the ionic compound as a subscript (small and down) after the symbol for the ion E.g. MgCl2 (not Mg2Cl4) Ladies and Cations first But don’t write any of the ones Should be the smallest ratio

How do they look together? Determine the group. This will tell you how many electrons in the outer shell. Mg group is 2A. There are 2 electrons in the outer shell. Cl group is 7A. There are 7 electrons in the outer shell. Ladies and Cations first But don’t write any of the ones

How do they look together? Determine how many electrons are gained or lost. This will tell you the ionic charge. 2 < 4, 2 electrons lost for Mg. 12 –10 = charge of +2 for Mg. 7 > 4, 1 electron gained for Cl. 17 – 18 = charge of –1 for Cl. Ladies and Cations first But don’t write any of the ones

How do they look together? Determine how many of each ion you need to make an ionic compound. This will tell you the formula. Need 2 Cl- to balance out Mg+2 2(-1) + 2 = neutral charge for compound Ladies and Cations first But don’t write any of the ones

How do they look together? Write the formula, cation first, with the correct subscripts. Mg, the cation is first, and we need only 1. Cl, the anion is second, and we need 2. MgCl2 is the correct formula for the ionic compound. Ladies and Cations first But don’t write any of the ones

Will they stay together? If the bond between them is stronger than other forces pulling on them, they will stay together. However, many bonds in ionic compounds are weak enough that the polarity of water molecules pulls them apart to dissolve the solid crystals into solution. E.g. NaCl, table salt, dissolves in water to form salt water. Ladies and Cations first But don’t write any of the ones

Answers to Our Questions Why is the periodic table arranged the way it is? “Birds of a feather flock together.” How do you make an element happy? “Atoms think its great when they have 8, so they give and take until they have 8.”

Answers to Our Questions What does an atom look for in mate? “Opposites attract, and sometimes three (or more) is company.” How do they look together? “Ladies (and cations) first, and the positives balance the negatives.”

Answers to Our Questions Will they stay together? “Only if their bond is stronger than their attraction to others.”

Ionic vs. Covalent Compounds How do you know if a compound is ionic or covalent? Ionic compound = Metal bonded to non-metal (or polyatomic) Covalent compound = Non-metal bonded to non-metal