Chemistry
Chemistry
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The Metric System (page 12 - 13)
The Metric System (page 12 - 13)
Metric System/International System of Units (SI system in French), it's a system used to measure distance, length, volume, weight and temperature. It's based on three basic units in which we measure almost everything.
M- meter, used to measure the length.
Kg- kilogram, used to measure the mass.
Chemistry like most science depends on the SI.
The following table shows the SI system of units' seven base units.
SI Base Units
SI Base Units
Quantity ⋅ Unit ⋅ Symbol
Length ⋅ meter ⋅ m
Time ⋅ second ⋅ S
Mass ⋅ kilogram ⋅ kg
Temperature ⋅ Kelvin ⋅ K
Electric current ⋅ ampere ⋅ A
Substance amount ⋅ mole ⋅ mol
Luminous intensity ⋅ candela ⋅ cd
Occasionally, these units aren't very handy. We instead use the prefixes that are added to the previous units for easier use.
Selected Prefixes for Metric Units
Selected Prefixes for Metric Units
Prefix ⋅ Symbol ⋅ Meaning
giga ⋅ G ⋅ 1,000,000,000 or 10^9
mega ⋅ M ⋅ 1,000,000 or 10^6
kilo ⋅ k ⋅ 1,000 or 10^3
deci ⋅ d ⋅ 0.1 or 10^ -1
centi ⋅ c ⋅ 0.01 or 10^ -2
milli ⋅ m ⋅ 0.001 or 10^ -3
micro ⋅ m ⋅ 0.000001 or 10^ -6
nano ⋅ n ⋅ 0.000000001 or 10^ -9
pico ⋅ p ⋅ 0.000000000001 or 10^ -12
femto ⋅ f ⋅ 0.000000000000000 or 10^ -15
atto ⋅ a ⋅ 0.000000000000000000 or 10^ -18
Problem: Use metric prefixes to express the following measured values:
a) 0.0000075 meters
75 x 10^ -7
b) 25,000,000 grams
25 x 10^6
What's an Atom? (page 38 )
What's an Atom? (page 38 )
Atoms are the smallest unit of an element with the same properties as larger chuncks of that element.
There are 6.02 x 10^23 (602 billion trillion) hydrogen atoms in a gram. So atoms are typically count in a larger unit called "mole" instead individually.
Greeks
Greeks
Ancient Greeks were the first to think of the nature of matter. Democritus and Leucippus created the atomic theory and concluded that when the matter is divided, it is left with indivisible particles called atoms.
Atom comes from the Greek word "atomos", meaning indivisible. Philosopher Plato believed the existence of four elements (fire, air, earth, water) that were building blocks of all matter and that each of these had a unique shape, known today as the five 'Platonic solids'.
Despite having no evidence, this theory lasted very long. It was said in the dark ages that the Greeks knew everything there to know.
For two millennia, nobody tried to discover the nature of matter, until Antoine Lavoisier in the 18th century found that the products' weight of a chemical reaction was the same as the weight of the reactants, now known as the law of conservation of mass, which old news today.
E.g.: We make a sandwich with 100 grams of ham and 50 grams of bread, the final weight will be the 150. But imagine it's burned to ashes, we find that the remains only weight 50 grams.
Dalton's Law
Dalton's Law
Refers to the rules that John Dalton created in 1808 about atoms to devise a series of rules describing the atoms' behavior (although some are false):
All matter is made of tiny, indestructible particles called atoms.
All atoms of a given element are identical. For example, if you purify gold by two different methods, each atom of gold from either method will have the same chemical and physical properties.
Atoms are neither created nor destroyed in chemical reactions; they obey the law of conservation of mass. When chemical reactions take place, only the arrangement of atoms changes, not the weight.
Atoms of different elements form compounds in whole-number ratios. For thsi reason, chemical compounds have formulas like H2O, not H21O13.
It should be known that atoms can be destroyed through nuclear reactions. Atoms of the same element don't always have the same properties. Overall, Dalton didn't do so badly, considering that he hadn't see atoms directly.
J.J. Thomson's Model
J.J. Thomson's Model
J.J. Thomson in 1897 did an experiment in which voltage was applied across two wires (electrodes) in a vacuum tube, resulting from this applied voltage, a glowing beam of particles was observed to travel from the cathode (negative electrode) to the anode (the positive electrode). Because of these light rays originated at the cathode, they were called creatively enough, cathode rays. With these magnets, Thomson was able to deduce that these rays contained particles with a negative charge. in his experiments, he placed the positive pole of one magnet on one side of the cathode ray tube and the negative pole of another magnet on the other. When the cathode ray tube was turned on, the ray was reflected away from the negative pole and to the positive pole, telling him that the cathode rays is made of particles with a negative charge. He placed the positive pole of one magnet on one side of the cathode ray tube and the negative pole of another magnet on the other. When the cathode ray tube was turned on, the ray was deflected away from the negative pole and toward the positive pole. This indicated to Thomson that the cathode rays consisted of negative-charged particles.
He found that the electron mass was tiny compared to the overall atom mass, leading him to think that electrons are very small and light when compared to whatever contained the positive charge in an atom.
The "plum pudding" model for the atom was created (as it resembles a plum). It shows negative charges (electrons/plums) wandering in a positively charged area (pudding). As not many know what's a plum pudding, a chip cookie is a more modern example.
Rutherford's Discovery
Rutherford's Discovery
The discovery of radioactivity made many a new thing to study.
For decades, three radiation types were discovered:
Alpha radiation - helium nuclei with a 2+ charge
Beta radiation - electrons and
Gamma radiation - very energic light
Ernest Rutherford played in his lab by shooting alpha particles at a thin gold foil piece to see how they would be deflected by the cloud of positive charge suggested by Thomson. As most particles shot straight as expected, some were deflected at very large angles. Some even flew back to the radiation source - a discovery.
He eventually explained what he found with a non-dessert-related model. Instead of positive charges as a group, he believed that the positive charge was concentrated in the atom's nucleus with the negative ones floating around.
What we believe now
What we believe now
We know that the basic parts of the atom are the protons and neutrons located in the nucleus and the electronc in "orbitals" outside the nucleus. This table shows it:
Rutherford think that when positive alpha particles passed ear the positively chargefd nucleus, the resulting strong repulsion caused them to be deflected at extreme angles.
"Amu" stands for atomic mass unit.
Atoms' proton numbers identifies what the element is.
Hydrogen has one proton, no matter how many neutrons or electrons it has. Having as much protons as electrons makes it neutral as positive and negatives charges cancel each other out.
Isotopes
Isotopes
Isotopes are atoms of the same element with different masses. Proton and electron amounts are the same for all elements' isotopes, but neutrons are different, causing each isotope to have different atomic masses. In many atoms, neutrons can vary to stabilize the positive charge in the nucleus.
Examples of isotopes can be these three hydrogen - all having a proton and the rest having neutrons.
A, X, Z Notation
A, X, Z Notation
Three symbols are used to tell elements apart:
Z - atomic number, number of protons in the atom
A - atomic mass, number of protons and neutrons
X - atomic symbol that on the periodic table denoting each element
Average Atomic Masses
Average Atomic Masses
The average atomic mass of elements is the weighted average of the masses of all of its isotopes.
1H's atomic mass is 1 amu. 19F's is 19 amu. As all elements have more than an isotope, average atomic masses on the table are all listed as decimals.
abundant: sufficient amount
Average atomic mass equation = (mass of isotope 1) + (abundance of isotope 1) + (mass of isotope 2) + (abundance of isotope 2) + ...
E.g.
Isotope Isotope Mass/Amu Abundance
6F 6.015 7.5% = 0.075
7F 7.016 92.5% = 0.0925
6.015 (mass of 6F) x 0.075 (abundance of 6F) + 7.016 (mass of 7F) x 0.0925 (abundance of 7F)
= 0.451 amu + 6.490 amu
= 6.941 amu
Electron Configuration
Electron Configuration
Mixtures
Mixtures
Components in mixtures may or may not exist in the same phases. For instance, in a mixture of two solids, each solid may be dissimilar in comparison. In mixtures of two liquids, there may or may not be more than one phase - liquids that dissolve in one another. It's rare to find mixtures of more than two or three liquids that don't dissolve one another, called multiphase liquid mixtures.
An example would be oil and vinegar.
Homogeneous Mixtures: When two pure substances are mixed evenly, the result is called a homogeneous mixture or a "solution". It can usually be identified by looking. If something has more than one pure material and appears uniform, it might be homogeneous.
Uniform: absence of visible changes, in Chemistry.
Colloids
Colloids
Colloids are materials where a type of particle is suspended in another one without dissolving, making these somewhere between solutions and heterogeneous mixtures.
There are many colloid types, categorized by the phases of matter they have.
Main types are:
Aerosol comprises liquid or solid particles in a gas, like smoke or fog.
Foam is formed when a gas is suspended in liquid or solids, like shaving cream or marshmallows.
Emulsion is formed when particles of a liquid are suspended in other liquids or solids, like mayonnaise or butter.
Sol is made when solid particles are suspended in liquids, like paints gelatin, or blood.
A way to identify a colloid from solutions is by shining light through it. Because molecules in tiny (mostly one), they don’t reflect light. But colloids have particles big enough to reflect light, making light beams visible in colloids, but not solutions. This effect is the Tyndall effect.
Methods to separate mixtures
Methods to separate mixtures
Filtration is one of the simplest ways. If one of the substances is a liquid and the one, a solid, it’s as easy as pouring the whole mixture through filter paper. An example is in coffee makers, coffee passes through paper filters, but the ground don’t.
Distillation is mostly used when compounds dissolve in another, or when two liquids are mixed. A Bunsen burner or hotplate is used to heat mixtures. As the substances present in a mixture have different boiling points, one will boil sooner or later than the other. The vapor from the compound can be collected from a condenser, allowing it to be isolated in pure forms.
Chromatography is done by placing a mixture of two or more chemicals into a glass column filled with silica. When an organic solvent such as ethyl acetate or alcohol is poured through the column, one of the substances of the mixture will tend to stick to the silica better than the other, making the less sticky one to pass the column quickly, as for the stickier one to do later.
Extraction can be used when salt is dissolved in oils. By finding a liquid that isn’t soluble with the first one and that’s better at dissolving the salt than the oil is. When the two liquids are mixed, the salt moves from the oil to the water.
References
References
[1] Chemistry, The Complete"Chemistry, The Complete Idiot's Guide - Alpha Edition
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