Ions & Isotopes What is an ion? Charge by Group Valence Electrons by Group Lewis Electron Dot Structures What is an isotopes? Average Atomic Mass

Interpret the periodic table to describe an element’s atomic makeup Determine the Lewis electron-dot structure or number of valence electrons for an atom of any main group element from its atomic number or position on the periodic table.

Quick Review Atoms are made up of three particles: Protons Neutrons Electrons Which of the three particles identifies what element an atom is? The PROTON! (very important)

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. Example: Carbon (C) ALWAYS has 6 protons, but it can have anywhere from 6-8 neutrons and 2 or 10 electrons.

What is an ION? An ion is an element with a charge. Number of protons not equal to number of electron How are ions formed? By GAINING or LOSING electrons Atoms gain or lose electrons to become more stable. Their goal is to have a full outer energy level With 8 valence electrons (Octet Rule) Look like nearest Noble Gas

Positive Ions It is called a cation. When an atom LOSES electrons, it becomes more POSITIVE The atom is getting rid of negative particles (electrons) but the number of positive particles (protons) stays the same Why? To have a full outer energy level

Negative Ions It is called an anion. When an atom GAINS electrons, it becomes NEGATIVE Electrons have a negative charge, so the more you have, the more negative you become Why? To have a full outer energy level

Examples - Ions O-2 K+ N3- Ca+2 oxide ion with a negative 2 charge Gained 2 electrons K+ potassium ion with a positive 1 charge Lost 1 electron N3- nitride ion with a negative 3 charge Gained 3 electrons Ca+2 calcium ion with a positive 2 charge Lost 2 electrons

Valence Electrons Electrons in the outer most energy level of an atom. Most directly involved in chemical bonding & chemical reactions. Easy to determine based on element’s location on the periodic table. Elements gain and lose valence electrons to become an ion.

Determining Valence Electrons The # of valence e- an atom has is determined by the group the element is in on the periodic table Groups are the vertical columns on the periodic table (top to bottom) GET OUT YOUR PERIODIC TABLE SO WE CAN LABEL: Valence electrons and charge

Group 1 – Alkali Metals Elements in group 1 have only 1 Valence e- They form ions with a charge of +1

Group 2 - Alkaline Earth Metals Elements in group 2 have 2 Valence e- They form ions with a charge of +2

SKIP THE TRANSITION METALS – they are weird

Group 13 Elements in group 13 have 3 Valence e- They form ions with a charge of +3

Group 14 Elements in group 14 have 4 Valence e- They form ions with a charge of + or - 4

Group 15 Elements in the group 15 have 5 Valence e- They form ions with a charge of -3

Group 16 Elements in the group 16 have 6 Valence e- They form ions with a charge of -2

Group 17 – Halogen Elements in group 17 have 7 Valence e- They form ions with a charge of -1

Group 18 – Noble Gases They have full outer energy level Elements in group 18 have 8 Valence e- They DO NOT form ions because they stable . They have full outer energy level

EXCEPTION But what about Helium? It only has 2 e- so it can only have 2 e- in its Valence Shell

Lewis Electron-Dot Structures

Lewis Electron-Dot Structures All you have to do for a Lewis Structure is draw dots around an Element’s Symbol Number of dots you draw for a Lewis Structure is equal to the # of Valence Electrons

Group 1 – Lewis Structure All Elements in group 1 would have a Lewis Structure like this: H

Group 2 – Lewis Structure All Elements in group 2 have a Lewis Structure like this: Be

Group 13 – Lewis Structure 3 Valence e- Lewis Structure like this: B

Your Turn In the space provided in the table in your notes, you draw the Lewis Electron-Dot Structure for the element in the named group . . .

What is an ISOTOPE? An ISOTOPE is a form of an element that has a different number of neutrons Carbon has three isotopes: Notice the number of protons DOES NOT CHANGE

Representing Isotopes Have a different mass because the number of neutrons changed. Representing an isotope: Element Name – mass number Nuclear Symbol Chlorine – 35 Chlorine – 37

Example: Isotopes For each of the following isotopes of carbon, find the number of protons, neutrons, and electrons: Carbon – 12 Carbon – 13 Carbon – 14 Protons 6 Neutrons 12-6 = 6 13-6 = 7 14-6 = 8 Electrons

Average Atomic Mass Listed on the periodic table Gives the mass of “average” atom of each element compared to 12C Weighted average based on all the isotopes and their percent abundance. Atomic mass is not a whole number mass number is a whole number

Calculating Atomic Mass What you need: Percent(%) abundance of each isotope Mass Number of each isotope of that element Average Atomic Mass= Mass of isotope * percent abundance as a decimal + Mass of isotope * percent abundance as a decimal + Mass of isotope * percent abundance as a decimal . . . For all naturally occurring isotopes of an element

Example 1: Atomic Mass 24Mg 24.0 amu 78.70% 25Mg 25.0 amu 10.13% Isotopes Mass of Isotope Abundance 24Mg 24.0 amu 78.70% 25Mg 25.0 amu 10.13% 26Mg 26.0 amu 11.17% Atomic Mass = 24.0*0.7870 + 25.0*0.1013 + 26.0*0.1117 Atomic Mass = 24.3 amu

Example 2: Atomic Mass Calculate the average atomic mass where there is 69.15% copper-63 which has an exact mass of 62.929601 amu and 30.85% copper-65 which has an exact mass of 64.927794 amu. Average Atomic Mass = 62.929601*0.6915 + 64.927794*0.3085 Average Atomic Mass = 63.55 amu

Example 3: Atomic Mass Without doing any math, are there more Bromine-79 isotopes or more Bromine-80 isotopes on earth? According to the periodic table, the average atomic mass of bromine is 79.904, which is closer to 80 than 79. So there are more Bromine-80 isotopes on earth.

Example 4: Atomic Mass Neon has two major isotopes, Neon-20 and Neon-22. Out of every 250 neon atoms, 225 will be Neon-20 (19.992 g/mol), and 25 will be Neon-22 (21.991 g/mol). What is the average atomic mass of Neon? Average Atomic Mass of Neon =