Quarterly Review 3
ATOMIC CONCEPTS
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MODEL OF ATOM HAS EVOLVED OVER A LONG PERIOD OF TIME BY MANY
SCIENTISTS
THE ATOM HAS A NUCLEUS WITH A POSITIVE CHARGE (PROTONS) WITH
NEUTRAL NEUTRONS ALSO IN IT. IT IS SURRONOUNDED BY NEGATIVE
PARTICLES CALLED ELECTRONS. (THEY HAVE VIRTUALLY NO MASS)
RUTHERFORD (GOLD FOIL- NUCLEUS IS DENSE, POSITIVELY CHARGED AND
VERY SMALL. ATOM IS MADE UP OF VIRTUALLY EMPTY SPACE)
BOHR- ELECTRONS TRAVEL OUTSIDE THE NUCLEUS IN DISCRETE PATHS
CALLED ENERGY LEVELS
THE NUMBER OF PROTONS IS ALWAYS EQUAL TO THE NUMBER OF
ELECTRONS. REMEMBER, THE PROTON IS EQUAL IN MASS TO THE
NEUTRON THAT NUMBER IS 1 AMU. THE ELECTRON IS MUCH LIGHTER THAN
THE PROTON AND NEUTRON AND ITS MASS IS CONSIDERED NEGLIGIBLE.
THE WAVE MECHANICAL MODEL IS THE MOST UP TO DATE MODEL.
CONTINUED ATOMIC CONCEPTS
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WITH THIS MODEL, SCIENTISTS WERE ABLE TO SHOW THE LOCATION OF
THE ELECTRON IN PLACES CALLED ORBITALS.
AN ORBITAL IS A REGION IN WHICH THE ELECTRON CAN BE FOUND. IT IS
THE REGION OF HIGHEST PROBABILITY. THIS IS THE GROUND STATE.
WHEN AN ELECTRON IN AN ATOM GAINS A SPECIFIC AMOUNT OF ENERGY,
THE ELECTRON LEAVES THE GROUND STATE (LOWEST ENERGY) AND
ENTERS INTO A HIGHER ENERGY LEVEL (EXCITED STATE)
AT THIS POINT, THE ELECTRON HAS ABSORBED ENERGY.
WHEN THE ELECTRON RETURNS FROM A HIGHER ENERGY LEVEL TO A
LOWER ENEGRY LEVEL, A SPECIFIC AMOUNT OF ENERGY IS EMITTED.
THIS ENERGY CAN BE USED TO IDENTIFY THE CHARACTERISTICS OF
ELEMLENTS. WE USE A BRIGHT LINE SPECTRA FOR THESE IDENTIFICATION
PURPOSES. FLAME TESTS, FIREWORKS AND NEON LIGHTS.
CONT. ATOMIC CONCEPTS
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VALENCE ELECTRONS- OUTERMOST ELECTRONS IN AN ATOM. WE CAN FIND
THE VALENCE IN THE LAST SHELL. THEY CAN BE AS LITTLE AS ONE AND AS
GREAT AS EIGHT.
A FULL VALENCE MAKES THE ATOM HAPPY. THE NUMBER OF VALENCE
ELECTRONS ARE EQUAL TO THE NUMBER OF DOTS IN A LEWIS DOT
DIAGRAM.
ISOTOPES- FOR A PARTICULAR ATOM MAINTAIN THE SAME NUMBER OF
PROTONS BUT DIFFERENT NUMBER OF NEUTRONS. THEREFORE, THE
ATOMIC NUMBER STAYS THE SAME AND THE ATOMIC MASS INCREASES
FROM ITS ORIGINAL NUMBER. BEST EXAMPLE IS CARBON 12 AND CARBON
14. CARBON 14 HAS TWO MORE NEUTRON S THAN CARBON 12.
The average atomic mass of an element is calculated by taking the percentage
(convert to a decimal) and multiply by the atomic mass. Add all of those
products up to get the average atomic mass. This is considered to be the ratios
of the naturally occurring isotopes.
PERIODIC TABLE
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The elements are arranged by order of increasing atomic number
Similar properties for elements must mean that they are in the same group or
family. (activity, number of valence electrons, form positive or negative ions,
etc….l)
Sums of protons and neutrons for a given element tells which isotope we have for
that element. C-14 is the same as writing 14C.
Elements can be classified as metals (2/3 of the chart), nonmetals (to the right of
the staircase), and semi-metals (metalloids) borders the staircase (all except Al,
Po, and At.
Group 18 Noble Gases, Group 17 Halogens (F and Cl are gases, Br is a liquid, and
I is a solid)
Elements can be differentiated by their physical properties-density, conductivity,
malleability, ductility, solubility, hardness etc….
Elements can also be classified by their chemical properties-how an element
behaves during a chemical reaction (how it reacts with oxygen to form an oxide,
does it burn to form a different compound etc….)
Periodic Table
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Elements can also exist in two different forms. These are called allotropes.
These elements exist as two or more forms in the same phase. They differ in their
physical and chemical properties. For example, oxygen vs. ozone and coal vs.
graphite vs. diamond.
If you are looking for an unknown elements group in a compound, undo the SOB
method. For example, XCl2 The two from the chlorine comes up to the X and the
one from the X comes up to the chlorine. Therefore, the X comes from group 2.
In a group of metals, as we go from top to bottom, the ionization and
electronegativity go down. The atomic radius and metallic character go up.
Ionization energy- the amt. of energy necessary to pull off the most loosely held
electron of an atom in its gaseous state.
Electronegativity- a number based on a scale of .7-4.0, that determines an atoms
liking for electrons. F is the highest and Fr is the lowest.
Group 14 and 15 have metals, non-metals, and metalloids present in their group.
Atomic vs. ionic radii- metals, the atomic radii is larger than the ionic radii due to
a loss of a shell. Non-metals, the ionic radii is larger than the atomic radii due to a
gain of outer shell electrons.
Moles and Stoic.
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Compounds- two or more elements that are chemically combined
and can be broken down by ordinary chemical means. The
compound NaCl means that we have one mole-atom of sodium
and one mole-atom of chlorine.
► Empirical Formulas- is the simplest whole-number ratio of atoms
of the elements in a compound. If the empirical formula is CH,
the molecular formula could be C2H2. The formula mass is 26
and the empirical mass is 13.
► In all chemical reactions, there is always a conservation of mass,
energy and charge.
► The coefficients in a balanced chemical equation gives the mole
ratios for the reactions. These are called the mole-mole ratio.
► Formula mass- is the sum of the atomic masses of its atoms.
Molar mass- equals one mole of that substance. For example,
one mole of NaCl is equal to 58 grams. That is derived from 23
g for Na and 35 g for Cl.
► The percent composition by mass is calculated by adding the
mass of each element and multiplying it by the number of atoms.
That is your total formula mass. Then apply the part over the
whole x 100 to get the % by mass
Moles/ Stoic. Cont.
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There are many types of chemical reactions. Here are
just a few:
Synthesis A + B yields C
Decomposition C yields A + B
Single Replacement A + BC yields AC + B
Double Replacement AB + CD yields AD + CB
Neutralization Acid + Base yields Salt and Water
Combustion Gas + Oxygen yields Carbon Dioxide and
Water Vapor
Redox All reactions except Double Replacement and
Neutralization
If a gas or precipitate forms, then you know the reaction
has gone to completion.
For most reactions to occur that include metals, one
metal must be more reactive than the other.
Bonding
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Two major categories of compounds are IONIC AND COVALENT
Covalent is sharing. If they share equally, then the bond is non-polar covalent. If they
share unequally, then the bond is polar covalent.
All diatomic molecules (HOFBrINCl) are non-polar covalent. Their electronegativity
difference is 0.
All non-symmetrical molecules (bent – water, pyramidal – ammonia, and Hydrogen
Chloride etc….) are considered to be polar covalent.
All symmetrical molecules (CF4 , CH4 and all the diatomics) are also considered to be
non-polar covalent.
If a metal is combined with a non-metal or a polyatomic ion (table E) then the bond is
ionic (positive and negative ion) Also, two polyatomic ions bonded together are
considered to be ionic in nature.
In the reaction 2Na + Cl2 yields 2NaCl, the chlorine is one of the reactants that happens
to be bonded to itself. It takes energy (absorbed) to break the Cl-Cl bond.
Once the bond is reformed to obtain the product NaCl, then the energy is released to
reform the new bond.
Bonding cont.
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When one atom bonds to another atom, the goal of each atom is to achieve
noble gas stability. That is eight in the outer valence shell.
We use Lewis Dot Diagrams to show how atoms bond to one another. The
valence electrons are the only electrons used in the Lewis structures.
Remember, metals form + ions thereby losing electrons and non-metals form
– ions thereby gaining electrons.
If the electronegativity difference between two atoms in a molecule or
compound is less that 1.7, then the bond is covalent. If it is greater than 1.7,
then the compound is ionic. NaCl is ionic. The e value is greater that 1.7 and
it is a metal bonded to a non-metal.
If the bond is non-polar, then the molecule is always a non-polar molecule.
If the bond is polar, then the molecule can be polar (check asymmetrical
charge distribution) or the molecule can be non-polar (symmetrical charge
distribution)
If you have a metal bonded to a polyatomic ion (table E), then there are
always two types of bonds (usually covalent and ionic)
Network Solids- Diamonds and quartz
Coordinate covalent bonding- ammonium and hydronium. One element shares
its electron pair while the other bonded atom does not.
Hydrogen bonding is intermolecular in nature. It is always between a highly
electronegative non-metal and hydrogen. Water has one of the highest boiling
points of any liquid due to hydrogen bonding.
If you are a molecular solid, you have covalent bonds, you are soft, a poor
conductor and have a low Melting and boiling point.
Physical Behavior of Matter
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Matter is a pure substance or a mixture of pure substances
Three phases of matter: solid, liquid and gas.
Elements- are pure substances that are made up of the same types of
atoms. Elements cannot be broken down.
Compounds- made up of two or more atoms that are chemically
combined. Compounds can be broken down by ordinary chemical
means.
Mixtures are made up of two or more substances that can be
separated by physical means. We can either have a homogeneous or
heterogeneous mixture. Homogeneous mixtures are called solutions.
Mixtures can be separated by density, particle size, molecular polarity,
boiling and freezing points, and solubility.
In a solution, the solute gets dissolved (NaCl) and the solvent does the
dissolving (water) Remember, likes dissolve likes (water will dissolve
other polar molecules as well as ionic) Unlikes do not dissolve unlikes.
(water will not dissolve organic molecules such as gasoline, certain
alcohols, ketones etc….that are all non-polar covalent.
Physical Behavior of Matter cont.
Solubility curve- on the line-saturated, above the linesupersaturated, below the line- unsaturated per 100 g of
water at a specific temperature.
► If you are given 50 g of water, take ½ of the answer. If
you are given 200 g of water, then double the answer.
► Solubility Guidelines- if the material is a good electrolyte,
then it must be soluble. If you use the guidelines, always
check the guidelines. There are exceptions to the rules.
► Concentration- is measured in moles/liters. The term we
use is Molarity.
► If we place sugar, salt, alcohol in separate beakers, the salt
tends to lower the freezing point and elevate the boiling
point the most. This is due to the fact that salt ionizes into
two ions and alcohol and sugar do not ionize.
► If we have three separate salts, the salt with the greatest
number of ions will lower the fp and raise the bp the most.
(NaCl,BaCl2,AlCl3) The AlCl3 lowers the fp and raises the bp
the most due to 4 ions vs 3 ions vs 2 ions.
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Physical Behavior of Matter cont.
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Heat is a transfer of heat energy from a body of higher temp. to a body of
lower. The higher the temperature, the faster the molecules move.
In a heating and cooling curve, we start with a solid, then go to a solid-liquid
(melting/freezing point), then to a liquid, then to a liquid-gas
(evaporation/condensation), then to a gas.
In the solid, liquid, and gas states, KE is always increasing as you climb up the
curve. In the solid-liquid and liquid-gas phase, there is no KE but all increasing
Potential Energy.
If there is a change in temperature, use the formula m x c x ΔT.
If there is no change in temperature and the substance is either freezing or
melting, use m x Hf. If there is no change in temperature and the substance is
either evaporating or condensing, then use m x Hv. Hf, Hv, and C are all found
on the front of the reference charts.
Temperature- is the measure of the average KE of the particles in a sample of
matter. Temp. is not a form of energy.
Physical Behavior of Matter cont.
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Ideal gases- the model works if the pressure is very low and the temperature is very
high. In order to behave in an ideal way, gases should have no appreciable volume
and no apparent attraction toward one another.
Real gases- for a real gas to behave like an ideal gas, the above characteristics must
be obeyed. Otherwise, a real gas will have an appreciable volume and some apparent
attractive force between the molecules. Therefore, high pressure and low
temperature. Molecules move close together.
Kinetic Molecular Theory for ideal gases►
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Gases are in random, straight-line motion
Gases are separated by great distances and their volume is considered to be
negligible.
Gases have no attractive forces between themselves.
Gases may collide with each other, but the total energy of the system must remain
constant.
Gases follow the general formula called the General Gas Law- PV/T=PV/T
Physical Behavior of Matter cont.
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As the pressure rises, the volume falls with constant temp. The graph is an inverse
relationship.
As the temperature rises, the volume also rises with constant pressure. The graph is a
direct relationship.
Chemical and Physical changes can be either exothermic or endothermic.
If the change in heat (enthalpy) is negative and the heat of the products is less than the
heat of the reactants, the reaction gives off heat and is exothermic.
If the change in heat (enthalpy) is positive and the heat of the products is greater than
the heat of the reactants, the reaction absorbs heat and is endothermic.
The terms that you should know: activation energy- arrow drawn from the reactants to
the activated complex. PE of the reactants- arrow drawn from the x-axis to the reactants.
PE of the products- arrow drawn from the x-axis to the products. The change in heatthe arrow drawn between the products and the reactants. It is either positive or
negative.
The only thing that a catalyst changes is the activation energy and the rate at which the
reaction proceeds. There is no change in enthalpy, PE of reactants or products.
Kinetics and Equilibrium
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The rate of reaction is influenced by temperature, surface area and concentration. The
higher the temp, the greater the surface area and the more reactant you have, all leads to a
greater REACTION RATE.
► Catalysts only speed of the rate of reaction. If the reactants are of the proper orientation
(they collide head on) the reaction rate.
► We can have different types of equilibria. Solution equilibrium and phase equilibrium.
Saturated solutions are always at equilibrium. When we go from a liquid to a gas and a gas
back to a liquid, we have phase equilibrium.
► At equilibrium, the rate of the forward always equals the rate of the reverse. The quantities
of the products and reactants always remains constant at equilibrium. If the concentration
of the reactants is greater than the products, then the equilibrium constant is small and the
reactants are favored. If the concentration of the products is greater than the reactants,
then the equilibrium constant is large and the products are favored.
Kinetics and Equilibrium cont.
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Using the following reaction, we will study LeChatelier’s Principles:
N2 + 3H2→ 2NH3 + heat (EXOTHERMIC REACTION)
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If the pressure increases, then seek out the side with the fewer number of moles. The left
side has the fewer number, therefore, the reaction shifts left to right.
If the pressure decreased, then seek out the side with the greater number of moles. The left
side is favored, therefore, the reaction shifts right to left.
If the concentration of one of the reactants increases, (nitrogen) then the concentration of
the other reactant decreases (it gets used up faster) and the reaction shifts from left to right
making the concentration of the product increase.
If the concentration of one of the reactants decreases, then the reaction will shift from right
to left to fill the void. The concentration of the product decreases and the concentration of
the other reactant increases.
If the temperature of the reaction increases, then move away from the heat. Therefore, the
reaction will shift from right to left and the concentration of the product decreases and the
reactant increases.
If the temperature of the reaction decreases, then move toward the heat. Therefore, the
reaction will shift from left to right and the concentration of the produce will increase and
the concentration of the reactants will decrease.
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Kinetics and Equilibrium cont.
Using a cold pack, the heat flows from the injured leg or arm to the cold pack.
In order for a cold pack to work, the chemical must combine with the liquid in
the cold pack. The heat that the liquid has is used to dissolve the chemical.
Therefore, this reaction is endothermic and heat is absorbed.
► Using a heat pack the, heat flows from the pack to the injured leg or arm. The
reaction is exothermic because the heat flows from the pack out to the body.
This is a releasing of heat.
► Entropy-is the amount of disorder in a system. Solids have the most order
therefore minimum entropy. Gases have the greatest disorder, therefore
maximum entropy.
► Systems in nature tend to go toward lower energy –H and higher entropy +S.
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