1. Isotopes and Ions

2. Quotes about atoms From A Short History of Nearly Everything by Bill Bryson “protons give an atom its identity, electrons its personality” p. 140 “if an atom were expanded to the size of a cathedral, the nucleus would be only about the size of a fly- but a fly many thousands of times heavier than the cathedral” p. 141

3. Parts of the atom: Proton: –+ charge –Located in nucleus –Role: identifies the atom Neutron: –no charge –Located in nucleus –Role: space out nucleus and add mass (stabilize the nucleus) Electron: –- charge –Located in orbital's outside of nucleus (energy levels) –Role: perform all bonding of atom, give it charge

4. Atom Model

5. Atomic Number Found at top of each element square Represents the number of protons in atom If atom is “neutral” number of protons = number of electrons

6. Atomic Mass # at bottom of each element box = # of protons + # of neutrons To find # neutrons, subtract atomic number from atomic mass Ex) C: atomic mass = 12, atomic # = 6, – # of protons = 6, –# of neutrons = 6, (12-6) –# of electrons = 6 (= to # of protons)

7. Atomic Symbols Shorthand way of writing information Write symbol for element Put atomic number in subscript in front of symbol Put atomic mass in superscript in front of symbol BASICALLY FLIPPED FROM P.T.

8. Atomic Symbol Example

9. What is an ion? Ion - an atom or group of atoms that has a positive or negative charge An ion forms when an atom gains or loses electrons (protons identify atom) How does an atom become an ion?

10. What is the charge on an electron? –negative If you have more electrons than protons the charge would be? –negative If you have more protons than electrons? –positive (extra protons)

11. Cation Positive charge –Cat-ions are pawwwwwsitive Formed by the atom losing electrons Metals (left side of periodic table) form cations Ca Ca 2+ + 2e - How many electrons did Ca start with? How many did it end with? 20 18

12. Anion Negative charge –An-ion is a negative ion Formed by the atom gaining electrons Non-metals (right side of periodic table) form anions O + 2e - O 2- How many electrons did O start with? How many did it end with? 8 10

13. Key Point If atom has more p+ than e-, it will be a cation, have a + charge If atom has more e- than p+, it will be anion, have a - charge

14. Ion atomic Symbol Can always tell p +, n o, e - from atomic symbol, Must include charge for ion! –Atomic # & atomic mass go on the LEFT –Charge goes on the RIGHT Ex:Al +3 –How many protons, electrons and neutrons?

15. What is an isotope? Isotopes are atoms of the same element with different atomic masses. They have different masses because they have different numbers of neutrons in the nucleus (remember, neutrons add mass and stability to the atom)

16. How do you write isotopes? There are different types of isotope notation: Carbon-14 C C These all tell us that we are dealing with an isotope of carbon with an atomic mass of 14. How many protons and neutrons are in these isotopes? –Protons = 6 –Neutrons = 14 – 6 =8

17. How many protons and neutrons in these? O N Hydrogen-3 protons = 8, neutrons = 16 – 8 = 8 protons = 7, neutrons = 15 - 7 = 8 protons = 1, neutrons = 3 -1 = 2

18. Ions & Isotopes Both ions and isotopes can be shown in the same symbol. –Atomic # & atomic mass go on the LEFT –Charge goes on the RIGHT –How many protons, neutrons and electrons S Protons= 16 Neutrons = 34-16 = 18 Electrons = 16 +2 = 18

19. Write your own Write symbols for the following: The ion with 17 protons, 18 electrons, 20 neutrons: The ion with 92 protons, 88 electrons, 146 neutrons: Cl - U +4

20. Key Points (atomic symbols) Mass Number (# on top) – use to find neutrons Atomic Number (# on bottom) – use to find protons Charge Symbol (to right) – use to find electrons

21. Average atomic mass So far all the atomic masses we have used have been whole numbers BUT there are not whole number masses on the periodic table WHY??? The numbers on the periodic table are AVERAGE atomic masses

22. Calculating average atomic mass Average atomic mass is calculated by taking the average of all the different isotope masses For example, if these were the only 5 atoms of carbon we had: Carbon-12, Carbon-12, Carbon-12, Carbon-14, Carbon-14 What would the average mass be? –12+12+12+14+14 / 5 = 12.8

23. We can’t possibly weigh every atom in the world though… So we have to average their abundances –How much of them exists in relation to total Using our example from before: Carbon-12, Carbon-12, Carbon-12, Carbon-14, Carbon-14 Abundance of carbon-12 = 3/5 = (0.60 relative abundance) 60% Abundance of carbon-14 = 2/5 = (0.40 relative abundance) 40% Calculate average mass: 12g(0.60) + 14g(0.40) = 12.8g SAME ANSWER!!! LESS WORK!!

24. Practice Problem #1 Calculate the average atomic mass of magnesium using the following data for three magnesium isotopes. Isotopemass (amu)% abundance Mg-24 23.98578.70 Mg-25 24.98610.13 Mg-26 25.98311.17

25. Practice Problem #2 Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following atomic masses and abundances in nature: Lithium-6, 6.017 amu, 7.30% Lithium-7, 7.018 amu, 92.70%

26. Key Points % of all isotopes has to add up to 100! Make sure to take %’s and convert to relative abundance (move decimal 2 places to right)

27. What happens when you change… Protons: number of protons is the same as the atomic number, protons are what define an element. –change the protons you change the element Neutrons: The neutrons add to the mass and stability to the element. –change the mass of the element (make an isotope) Electrons: The electrons balance the charge of the protons. –change the charge of the element (make an ion)

28. Marshmallium Lab On the BACK: –Calculate average marshmallow mass using the LONG way Find the mass of each marshmallow, add them all up and divide by the total number of marshmallows –Write a sentence about why the way on the front (read directions) is easier.