Lessons 18, 19

Life on the Edge

Valence and Core Electrons

Electron Shells - levels around nucleus where electrons can be found Atomic # - number of electrons

Period # - number of shells ex: period 1 has one shell, period two has to shells, etc...

Group # - number of valence electrons; this gives element in the same group some similarities

Valence Shell - outermost shell of atom

Valence electrons - electrons in the valence shell

Core electrons - all electrons not in valence shell

Noble Gas Envy

Ions

Ion - atom or group of atoms with a positive or negative charge because it lost or gained electrons

Metal atoms transfer electrons to nonmetal atoms when they form compounds.

• When the metal and nonmetal atoms combine they want to fill their valence shells to become like noble gases that have 8 in their valence shells
• They need to be balanced when they combine. This means that the total number of valence electrons of the two elements need to be a multiple of eight.

Ideally you want compound like elements from group 2 that have 2 valence electrons combining with an element from group 6 which have 6 valence electrons so their total valence electron count is 8. Or from group 1 combining with group 7. These all make it easier.

A lot of the time though The combinations can be with group 1 and group 6 which together only equal 7. However, if you add one more of the same element from group 1 that gives you 1 valence electron from each equalling 2 to add with the group 6 element, giving you 8 total.

For example: say you want to find the chemical equation for combining sodium, Na and oxygen, O. Sodium is in group 1 with one valence electron and oxygen is in group 6 with 6 valence electrons. By adding one more sodium atom it gives you 2 electrons to give to the oxygen atom to fill its she'll, giving you Na2O.

Cation - positive charge (metal)

Anion - negative charge (nonmetal)

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Lesson 17

Flame Test

In class we did a flame test where we held a metal rod dipped in different solution over a flame to observe what colors appeared.

• A flame test is a test used in laboratory to look for the presence of certain metal atoms
• The metal element in each chemical formula appears to be responsible for the flame's colors
• Only certain elements produce colorful flames

The colors in the flames are caused by excited electrons

• Electrons move away from the nucleus
• When they move back they release light energy

        Red                     Yellow-orange            Blue-green                    Pink-lilac
   Lithium, Li               Sodium, Na            Copper, Cu                    Potassium, K
Lithium chloride        Sodium chloride          Copper chloride           Potassium chloride
        LiCl                             NaCl                           CuCl2                              KCl

 Practice Problems

1) How did the flame test provide evidence that specific atoms are present in compounds? The colored flames each had recurring elements.
6) What evidence do you have from flame tests that copper is responsible for producing a flame with a blue-green color? Each blue-green flame had copper in its compound.
10) If two chemical samples both produce an orange flame upon testing, which statement is true? C- the samples both contain calcium atoms

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Lesson 16

Old Gold

Formation of Elements

Nuclear reactions change the identity of an element

Nuclear Fusion

• joins nuclei together changing the identity of the element
• smaller, lighter elements to a bigger, heavier element
• happens in stars

Nuclear Fission

• spontaneous reaction in unstable nuclei
• releases enormous amounts of energy
• nuclear chain reaction as a result

Sample Problems

2) what is a nuclear chain reaction? A nuclear chain reaction is when a neutron emitted by nuclear fission hits surrounding nuclei causing them to split too.

3) Write the nuclear equation for the beta decay of cerium-141.

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Lessons 13 & 15

Subatomic Heavyweights

Isotopes

Isotopes - atoms of the same element that have the same number of protons and electrons but different numbers of neutrons

Isotopes associate with the atomic number and the mass number of an element

• The difference in neutrons but not protons in an atom of an element means that the element doesn't change into another element and the atomic number stays the same while the atomic mass number changes
• Isotopes are referred to by their atomic mass number
• The average atomic mass number of an element on the periodic table is the weighted average of all the naturally occurring isotopes

- the isotope with the mass closest to the average atomic mass is the most common isotope
How do you write an isotope?

Hyphenotation: symbol - mass #

Nuclear notation: mass # with the symbol to the right . atomic #

Practice Problems

4) How many protons, neutrons, and electrons are in each?

a. Fluorine-23: 9,14,9     b. 59                          c. Molybdenum-96: 42,54,42 
                                      27 Co: 27,32,27 

5) An isotope of iron, Fe, has 26 protons and 32 neutrons.

1. What is the approximate mass of this isotope? - 58 amu
2. How would you write the symbol for this isotope? Fe-58

Nuclear Quest

Nuclear Reactions

Nuclear Reaction - a process that involves changes to the nucleus of an atom

Radioactive Decay - a spontaneous process by which an atom emits radiation or a particle from its nucleus to become more stable

• Changes in the nucleus of an atom can change the identity of an element

Alpha Decay

Alpha Decay - emits an alpha particle, atomic # decreases by 2 and mass # decreases by 4

Alpha particle - a particle composed of two protons and two neutrons, or the nucleus of a helium atom

Beta Decay

Beta Decay - neutron changes into proton and electron and atomic number increases by one

Beta particles - an electron emitted from the nucleus of an atom during beta decay

Since during beta decay an electron from the original element leaves, that means the atomic mass goes down by one. However, that neutron then changes into a proton and electron. Therefore, the atomic mass goes back up by one because of the proton and the new proton also cause the atomic number to go up by one making it a whole new element.

Gamma ray - a form of high-energy electromagnetic radiation emitted during nuclear reactions

Practice problems
4) Explain why the mass of an atom changes when an alpha particle is emitted. When an atom emits an alpha particle it is getting rid of 2 protons and 2 neutrons and since protons and neutrons make up an atom's mass, the resulting atom has a mass of 4 less.

6) An alpha particle is not a neutral atom. It has a charge of +2. Why is this? An alpha particle is basically a helium nucleus thus doesn't have electrons meaning the 2 protons make the particle positively charged.

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Lesson 12

Atoms by Numbers

Atomic Number and Atomic Mass

Atomic Number - the number of protons in an atom of an element; elements on the periodic table are arranged in order by atomic number

A neutral atom is one where the number of electrons and protons are equal, therefore balanced.

• The mass of an atom is made up of the protons and the neutrons
• Changing the number of protons in an atom Changes the identity of the element

Practice Problems

3) If you have a sample of atoms and each atom has 12 protons in its nucleus, which element do you have? Magnesium, Mg.
5) Why does carbon, C, gave a larger atomic mass than boron,B, even though they both have 6 neutrons? Carbon has a larger atomic mass because even though the neutron numbers are the same, it has more protons than boron.

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Lessons 6,9, and 10

Lesson 6 - A New Language

Chemical Names and Symbols

All matter in the universe is and element or a combination of elements.

Element - a unique substance that cannot be broken down into simpler substances through any chemical process. ex: Na or Sodium is an element on the periodic table.

Compound - a pure substance that is a chemical combination of two or morelements in a fixed ratio. ex: H2O is water and since H2O is a compound then this means that water is made up of 2 Hydrogen atoms and 1 oxygen atom.

• Compound are represented by chemical formulas. 

Chemical Formula - combination of symbols and subscripts that indicates the number and types of elements in a compound.

• Substances come in different physical forms called phases.

Phase - physical form a substance is in like solid, liquid, or gas.

Aqueous - when a substance is dissolved in water.

Practice Problems
3) How many elements are included in the chemical formula for sodium nitrate, NaNO3? Name them.
Three elements; sodium,Na, nitrogen, N, and 3 oxygen atoms, O3. 
4) What is the difference between NaOH(s) and NaOH(aq)? The s after the compound indicates that it's physical form is solid while aq indicates liquid. 

Lesson 9 - Create a Table

Properties of the Elements

Atomic Mass - the mass of a single atom (or isotope) of an element.

Reactivity - property describing whether an element or compound will chemically combine with other substances as well as the speed of the reaction.

• The periodic table is organized based on the properties of elements with columns of elements on the table share similar properties, reactivity, and atomic mass.

Practices Problems

2) Do you expect carbon,C, to be more similar to nitrogen, N, oxygen, O, or silicon,Si? Why?

Carbon should be more similar to silicon because they are in the same group and elements in the same group share properties. 

5) Suppose you have equal amounts of calcium, Ca, in two beakers. You react the calcium in one beaker with oxygen, O, and the other with sulfur, S. The reaction between calcium and oxygen forms compound CaO. 

1. What do you predict is the chemical formula of the compound formed from the reaction between calcium and sulfur? CaS
2. Which compound has more mass? Explain? The calcium and sulfur compound because their combined mass is 36 not 28. 

Lesson 10 - Breaking the Code

The Periodic Table

Atomic number - the atomic number of an element is the same as the number of protons in the atom of that element. Can be identified as the whole number associated with the element on the periodic table.

Group - a vertical column in the periodic table elements in the group sharing similar properties

Period - Horizontal rows on the periodic table.

Metals - elements that are excelled conductors of heat and electricity, shiny and malleable

Nonmetals - elements that are poor conductors of heat and electricity, dull and brittle, and found to the right of the stair-step line.

Metalloids - elements between the metals and nonmetals,

Practice Problems
5) Which of these elements are solids? B-Titanium,Ti  C-Lead, Pb  E-Poyassium, K  F-Silicon,Si.
6) Which of these elements are nonmetals? A-Bromine, Br  B-Carbon, C  E-Phosphorus, P

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Conversions

Conversions Between Metric Units

Prefixes

Kilo- 1000

Hecto- 100

Deka- 10

No prefix means one

Deci- 1/10

Centi- 1/100

Milli- 1/1000

Using liters as an example, there is 10 liters in 1 dekaliter and 10 dekaliters in 1 hectoliter. In turn this means there are 100 liters in 1 hectoliter.

Going the other way, there are 10 deciliters in 1 liter and 10 centiliters in 1 deciliter. So this means there are 100 centiliters in 1 liter.

Converting Within the Metric System

Converting 65.1 millimeters to dekameters.

• First convert to meters because that is the common unit. 65.1 millimeters x 1 meter/ 1000 millimeters
• So you want the millimeters in the denominator so that the two cancel out like this: 65.1 millimeters x 1 meter/ 1000 millimeters.
• Now since you have to multiply by 1/1000, that is the same as dividing by 1000. So it becomes 65.1/1000.
• 65.1 divided by 10 means you move the decimal to the left one space equalling 6.51, now 65.1 divided by 100 means moving the decimal to the left two spaces equalling .651, but we want one more so 65.1 divided by 1000 means moving the decimal over three spaces to equal 0.0651.
• So 65.1 millimeters = 0.0651 meters
• 0.0651 meters x 1 dekameter/ 10 meters ---> 0.0651 meters x 1 dekameter/ 10 meters.
• 0.0651/ 10 = 0.00651 deka meters
• So 65.1 millimeters = 0.00651 dekameters

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