2. ATOMS, IONS, AND ISOTOPES

3. QUICK REVIEW Atoms are made up of three particles:  Protons  Neutrons  Electrons Question: Which of the three particles identifies what element an atom is? The PROTON! (very important)

4. DIFFERENT FORMS OF THE SAME ELEMENT In any element, the # of protons is always constant. Unlike the number of protons, the number of electrons and neutrons can vary within an element without changing the identity of the element.  Ex. Carbon (C) ALWAYS has 6 protons, but it can have anywhere from 6-8 neutrons and 2-10 electrons

5. ISOTOPES An ISOTOPE is a form of an element that has a different number of neutrons than “normal” Carbon has three isotopes Notice how the # of protons does NOT change!

6. ISOTOPES Atoms that have the same number of protons, but have different numbers of neutrons Examples + - + - + - Hydrogen (Protium)Hydrogen (Deuterium)Hydrogen (Tritium) Notice that each of these atoms have one proton; therefore they are all types of hydrogen. They just have a different mass number (# of neutrons).

7. ATOMIC MASS The weighted average of the masses of all the naturally occurring isotopes of an element The average considers the percent abundance of each isotope in nature Found on the periodic table of elements Example + - + - + - Hydrogen (Protium) Mass # = 1 amu Hydrogen (Deuterium) Mass # = 2 amu Hydrogen (Tritium) Mass # = 3 amu If you simply average the three, 2 amu (1 amu + 2 amu + 3 amu/3) would be the atomic mass, but since 99.9% of the Hydrogen is Protium, the atomic mass is around 1 amu (.999 x 1 amu) What would be the atomic mass (≈) of Hydrogen if these three isotopes were found in the following percentages (99.9, 0.015, 0) respectively?

8. OTHER ISOTOPES Most atoms have naturally occurring isotopes including:  Radon  Potassium  Uranium When an element is “radioactive” it means it has an unstable number of neutrons (an unstable ISOTOPE)

9. IONS An atom usually has a neutral charge. That means it has the same number of protons as electrons  Remember, a proton has a positive charge and an electron has a negative charge ION – an atom that has lost or gained one or more electrons and has become charged either positively or negatively

10. Symbol = O 2+ ION Charged particle that typically results from a loss or gain of electrons Two types:  Anion = negatively charged particle  Cation = positively charged particle + + + + + + + - - - - - - - - + - Now that this atom of oxygen just gained an electron, it is no longer neutral or an atom. It is now considered an ion (anion). This ion has more electrons (9) than protons (8). + - = 8 96 Symbol = O 1- Now that three electrons were lost, the number of electrons (6) and protons (8) is still unbalanced; therefore, it is still an ion, but now it is specifically referred to as a cation. Currently, this atom of oxygen is neutral because it has an equal number of electrons (8) and protons (8). Symbol = O

11. POSITIVE IONS When an atom LOSES electrons, it becomes more POSITIVE  Why? If you are getting rid of negative particles (electrons) but your number of positive particles (protons) are staying the same.  In other words, you are subtracting negative numbers

12. EXAMPLES What would the charge be if: The neutral form of Gold (Au) lost 4 of its 79 electrons. It now has 79 protons and 75 electrons The neutral form of Mg lost 2 of its 12 electrons. It now has 12 protons and 10 electrons.

13. NEGATIVE IONS When an atom GAINS electrons it becomes more NEGATIVE  Why? Electrons have a negative charge, so the more you have, the more negative you become

14. REPRESENTING IONS Ions are represented by placing a “superscript” charge number next to the atomic symbol. Ex.  O -2 = oxygen with a negative 2 charge  K + = potassium with a positive 1 charge  N -3 = nitrogen with a negative 3 charge  And so on

15. BUILDING IONS Using the whiteboard and the proton, neutron, and electron pieces, build the following ions, and determine their atomic and mass numbers. IonsProtonsNeutronsElectrons Carbon (C³¯)669 Hydrogen (H¹+)100 Oxygen (O²¯)8810 Lithium (Li³+)340 Sodium (Na¹¯)1112 Be aware that the atomic and mass numbers are not impacted by the loss or gain of electrons.

16. PERIODIC TABLE The elements, as they are found on the periodic table, are neutral atoms and their mass is an average of all isotopes  Remember the atomic mass is the average of ALL isotopes, but when we round it for calculating the number of neutrons, we always get the most abundant isotope.

17. EXAMPLES

18. How many P’s, N’s, and E’s does each of the following have? Label each as an isotope, ion, or the version found on the P.T.