When Atoms Change …

When Atoms Change…

What we KNOW… • Atoms on the periodic table are neutral. • Atoms are neutral because they have the same number of protons as electrons. • protons have a positive charge. • neutrons have no charge. • electrons have a negative charge.

What we Also need to KNOW… • The identity of an atom is determined ONLY by the number of protons. • For example… If I tell you there is an atom with 3 protons… you know it’s a Lithium atom. • What about 8 protons, 13 protons, 79 protons???

What happens if the number of neutrons change??? If an atom gains Neutrons… 1. The mass increases by 1 for every neutron added. 2. The charge remains neutral. (Neutrons don’t have a charge.) 3. The number of protons and electrons stay the same. If an atom loses Neutrons… • The mass decreases by 1 for every neutron taken away. • The charge remains neutral. (Neutrons don’t have a charge.) • The number of protons and electrons stay the same.

The atom is now called an ISOTOPE! When atoms gain or lose neutrons!

ISOTOPE EXAMPLE Hydrogen Isotope Has a mass of 2 and an atomic number of 1

ISOTOPE NOTATION We communicate that we have an isotope by using the Atomic Symbol of the isotope followed by the “NEW” mass number. ISOTOPE NOTATION Li-6 Ex: An Isotope of Lithium is: Li - 6 Atomic Symbol Mass Number

Isotope INVENTORY Completing a particle inventory for an Isotope is almost the same as the neutral atom EXCEPT we USE THE “NEW” MASS NUMBERto calculate neutrons. Ex: Li-6 3p+ (since it’s Lithium!!!) 3e- (since they are still equal to p+) 3n (6-3 = 3)

Isotope Practice • Caatom has a mass of 40. • The isotopes for Ca are: • Ca-42, Ca-43,Ca-44, Ca-46, & Ca-48. • 1.) How many neutrons are in a Ca atomand each of its isotopes? 2.) What are the differences and similarities between the Ca atom and its isotopes?

Isotope Practice Ca atom has a mass of 40. (atomic # =20) The isotopes for Ca have masses of 42,43,44,46, & 48. 1.) How many neutrons are in a Ca atom and each of its isotopes? (Ca ATOM: 40 – 20 = 20n) (ISOTOPES: 42-20=22n, 43-20=23n, 44-20=24n, 46-20=26n, 48-20=28n) 2.) What are the differences and similarities between the Ca atom and its isotopes? Similarities Differences (The # of neutrons is different, masses are all different.) (All have 20 p+ all have 20 e- all neutral all are Calcium)

The Atom Building Game • Everyone gets 7 blue, 7 striped, 7 clear • Black = Protons • Red = Neutrons • White = Electrons • Play 1-5pieces per turn. Mass numbers 1,2 Number of neutrons and protons H Subtract the two to find the number of neutrons Atomic # 1 Number of protons and electrons

Everyday Uses of Isotopes Smoke Detectors and Americium-241 What most consumers don't know is that many of these units contain a small amount of americium-241. By utilizing the radioactive properties of this material, smoke from a fire can be detected at a very early stage. This early warning capability has saved many lives. In fact, studies have shown that 80% of fire injuries and 80% of fire fatalities occur in homes without smoke detectors.

Carbon-14Dating Recalling that all biologic organisms contain a given concentration of carbon-14, we can use this information to help solve questions about when the organism died. When an organism dies it has a specific ratio by mass of carbon-14 to carbon-12 incorporated in the cells of it's body. At the moment of death, no new carbon-14 containing molecules are metabolized, therefore the ratio is at a maximum. After death, the carbon-14 to carbon-12 ratio begins to decrease because carbon-14 is decaying away at a constant and predictable rate. Remembering that the half-life of carbon-14 is 5700 years, then after 5700 years half as much carbon-14 remains within the organism.

Food Irradiation Food irradiated by exposing it to the gamma rays of a radioisotope -- one that is widely used is cobalt-60. The gamma rays pass through the food to destroy many disease-causing bacteria as well as those that cause food to spoil. It’s not strong enough to change the quality, flavor or texture of the food. The food never comes in contact with the radioisotope and is never at risk of becoming radioactive!

Reviewing Isotopes Neutrons! What are isotopes gaining or losing? Here is an Atom of Oxygen (how many neutrons?) Atomic Mass=16 These are isotopes of Oxygen O-17 O-18 So…How many neutrons does each isotope of Oxygen NOW have? 8 neutrons 9N 10N

Isotope Practice 1.)How many neutrons are in each of Zinc’s isotopes? Zn-65 Zn-64____ Zn-67_____ Zn-70____ 2.) What are the differences and similarities between the Zn atom and its isotopes? Set-up a “T” Chart

Isotope Practice 1.)How many neutrons are in each of Zinc’s isotopes? Zn-65 Zn-64____ Zn-67_____ Zn-70____ 2.) What are the differences and similarities between the Zn atom and its isotopes? 34 37 40 Similarities Differences • # of neutrons is different • masses are all different • All have 30 p+ all have 30 e- • all neutral • all are Zinc

Isotope Practice 1.)How many neutrons are in each of Strontium’s isotopes? Sr-84____ Sr-86_____ Sr-87____ Answers: Sr-84 46 Sr-86 48 Sr-87 49

20 Quiz QuickIsotopes gain or lose… • electrons • protons • neutrons • nuclei

20 When an atom gains neutrons, its charge changes. • True • False

20 When an atom gains neutrons, the number of protons and electrons do not change. • True • False

19 The only subatomic particles that never change are… • Valance electrons • Protons • Electrons • Neutrons

What happens if the number of electrons change??? If an atom gains electrons… 1. The charge becomes negative. (There are more negative e- than positive p+ now!) 2. The mass stays the same (electron’s mass = 0). 3. The number of protons and neutrons stays the same. If an atom loses electrons… • The charge becomes positive. (There are less negative e- than positive p+ now!) • The mass stays the same (electron’s mass =0). 3. The number of protons and neutrons stays the same.

The atom is now called an ION!!! When atoms gain or lose electrons!*Ions are charged particles! Ions form so that unstable atoms can bond with other unstable elements to become a stable substance!

Charged Ions Anion (-) Negatively charged ion. Cation (+) Positively charged ion

19 Quick QuizIf an atom loses electrons, its mass changes? • True • False

20 Ions gain or lose… • isotopes • protons • neutrons • electrons

20 Gaining electrons causes atoms to… • Gain more mass • Have a charge • Stay neutral • Lose mass

ION EXAMPLE

Na Be I Ca Sb S P C Na+1 Be+2 I-1 Ca+2 Sb-3 S-2 P-3 C+/-4 Ion Practice

Li +1 Br -1 Mg +2 B+3 F -1 N -3 Cl -1 K +1 Ba +2 Te -2 Sn -4 As -3 Si +/-4 O -2 Al+3 Ion Worksheet Answers

Li +1 Br -1 Mg +2 B+3 F -1 N -3 Cl -1 K +1 Ba +2 Te -2 Sn -4 As -3 Si +/-4 O -2 Al+3 Ion Worksheet Coloring

What patterns did you notice from coloring your ions on the periodic table?*hint* there is more than one! • The families were the same color. • The families had the same ionic charge. • Metals have a positive charge. • Non-metals have a negative charge. • Metals lose electrons. • Non-metals gain electrons.

Practice Draw the Bohr models for the following elements and find the ionic charges for each. Rb Sr Bi Rb Sr Bi +1 +2 -3

Similar Same element Same # of protons Same # of electrons Same charges Different Different masses Different # of neutrons How is the neutral(no charge) atom Se and it’s isotope Se-78 similar and different?(Set up a “T” chart)

Similarities Same number of protons only! Differences Diff Masses Diff Number of neutrons Diff Charges Diff Number of electrons How are isotopes and ions similar and different? (setup a T chart)(hint* think about particles, masses and charges)

Practice Draw the Bohr models for the following elements and find the ionic charges for each. Ga P Pb Ga P Pb -5 -3 -4

Patterns on the Periodic Table

+1 0 Ionic Charges +3 +/-4 -3 -2 -1 +2

Valence Electrons 3 4 5 6 7 8 Valence e- 1 2

Energy Shells of Atoms Period 1 1Shell 2Shells Period 2 Period 3 3Shells Period 4 4Shells Period 5 5 Shells Period 6 6Shells Period 7 7Shells

Families/Groups have a lot in common… • We now know that elements in a group all have the same # of valence e-. • We also now know they all form ions with the same charge. • But…there are a lot of other properties that elements in a family also share! • Such as…Atomic Width, Ionization Energy, Electronegativity and reactivity.

Atomic Radius (Width) • Atomic radius is simply the radius (width) of the atom, an indication of the atom's volume. • Periods - atomic radius decreases as you go from left to right across a period. • Why? • Stronger attractive forces in atoms (as you go from left to right) between the opposite charges in the nucleus and electron cloud cause the atom to be 'sucked' together a little tighter. • Largest atomic species are those found in the SW corner of the periodic table.

Atomic Radius (Width) • Groups - atomic radius increases as you go down a group. • Why? • There is a significant jump in the size of the nucleus (protons + neutrons) each time you move from period to period down a group. Additionally, new energy levels of electron clouds are added to the atom as you move from period to period down a group, making the each atom significantly more massive, both is mass and volume.

Ionization Energy • Ionization energy is the amount of energy required to remove the outermost electron. It is closely related to electronegativity. • Group - ionization energy decreases as you go down a group. • Why? • The shielding effect makes it easier to remove the outer most electrons from those atoms that have many electrons (those near the bottom of the chart).

Electronegativity • Electronegativity is an atom's 'desire' to grab another atom's electrons. • Period - electronegativity increases as you go from left to right across a period. • Why? • Elements on the left of the period table have 1 -2 valence electrons and would rather give those few valence electrons away, as a result, they have low electronegativity. • Elements on the right side of the period table only need a few electrons, so they have strong desire to grab another atom's electrons.

When Atoms Change …