(term 1) Test 1 + 2 Chemistry (Exam)
Precision and accuracy:
Precision: Precise but not accurate (set of data that are close to each other but not on the target)
Accuracy: accurate but not precise (scattering further out but closer to the target than others)
Percent error: the lower it is the better the measurement, the higher it is the worse the measurement is
* So if you take the difference of theoretical value-experimental value/theoretical value (in reality you can switch the order of the subtractions to guarantee that you will get a positive result) then x100
*Always take the positive value
Example: a sample of wood has a density of .85 g/ml. You measure the density to be .91 g/ml
What is the percent error?
Answer: .91-.85/.85 = -0.09 x100
Matter:
Matter- anything that takes up space and has mass
Elements-can not be made more simple through chemical reactions
There are 118 of them today
02- because it is made of oxygen atoms it is an element
Compounds: substances formed by 2+ elements that are bonded together and can be broken down into similar substances through chemical reactions. Formed chemically.
Mixture: mixing at least 2 pure substances together physically.
heterogeneous mixture: you can see a visible difference that makes up the mixture
Homogeneous mixture: a combo of uniformly distributed substances, ex. Powerade
9/9/24
Chemical and physical properties:
Physical properties: characteristic of a substance that can be observed or measured without changing the substance's chemical composition. Ex. color, density, state, hardness, melting point, boiling point, smell, length, temperature, shine, volume, magnetism, mass, malleability, state, and conductivity.
Chemical Properties: characteristic of a substance that is observed during a chemical reaction and that involves a change in the substance's chemical composition. The ability to undergo a chemical change.
Ex. corrosion, acidity, color (if it is a reaction), flammability, ability to rust, oxidation (browning of foods), reactivity, and toxicity
Acidic: low ph
Basic: high ph
Physical change: change in the form or state of a substance without any change in its chemical composition. New form but no apparent chemical reaction. Chemical reaction must be visible.
Ex.
Cutting
Breaking
Sand+water, salt +water, sugar+water
Crystallization
Stretching
Crushing
Crumpling
melting/freezing/boiling
Mixing (if it can be separated)
Boiling water
Chemical change: one or more substances are transformed into one or more new substances with different chemical properties and compositions. Change pertains to one of the 6 senses.
Ex.
Smell (if it suddenly changes)
Digestion (acids help break down)
Combustion (explosion)
Baking (using yeast to rise a food)
Leaves changing color
Rusting
Rotting
Temperature change
Photosynthesis
Sour milk
9/12/24
The Periodic table
Dimitri Mendeleev-attempted to come up with a system to organize all known elements, he grouped them in order by their individual masses, from the lightest-heaviest. These masses would become known as atomic masses. He put elements in columns based on having similar properties.
He noticed that there could be other elements in these columns that they missed at the time, he would make predictions about elements that hadn’t been discovered yet, and he was always right about what they would look like
Difference between group v. period- groups are vertical and they contain elements that are similar to each other. You can also organize the periodic table by periods or rows, they vary in size from period to period. Each of the elements in a period does not really have any relationships with each other they only relate in the increasing mass. The atomic number is the number at the top that consecutively gets larger. The atomic number =#of protons.
Metals-everything to the left of the staircase is considered a metal with the exception of hydrogen
Properties:
They tend to have high melting points
They are good conductors of electricity and heat
They are very shiny
They are very malleable (bendable/shapeable)
*For metals, as you go down the chart, they tend to get more reactive
Nonmetal: to the right of the staircase
Properties:
Can be gasses, liquids, or solids but mostly gasses
If they are solid they are brittle with low melting points and very dull and bad conductors of electricity
For non-metals, they get more reactive as you go up the chart
Metalloids: in between metals in nonmetals, ex. Brittle but shiny
*anything on the periodic table that is written in black is a solid at room temperature
*if they are in blue (Br, Hg) it is a liquid at room temperature
*if they are red they are a gas at room temperature
*clear is mostly unknown
Main group: very important groups, some metals, nonmetals, and metalloids
transition metals: very complex but not as interesting
lanthanides/actinides(inner transition metals): they tend to be very heavy and rare elements that will not be studied very often, moved to the bottom for convenience and size purposes
Test 2 notes:
Aristotle v. Democritus - they were philosophers
Democritus- when it comes to matter you canstart dividing and dividing until it can broken down to the smallest possible form = atoms (finite). Good idea, but no evidence.
Aristotle-he believed that matter was continuos and can always be divided further than it already is, people believed him more than Democritus, Aristotle was also born after Democritus died.
Law of conservation of mass:
Antoine Lavoisier: he was a tax collector who was executed, he is considered the father of chemistry.
* Mass is not created nor destroyed
*The table shows an example of rusting
Law of definite proportions: a chemical compound that always contains the same elements in the same proportions by mass, every compound is built the same way every time =definite proportions. You can't just add extra amounts of elements to the set “recipe”
Law of multiple proportions: about multiple compounds made from the same elements. When two elements form more than one compound the ratios of the masses of one element that combine with a fixed mass of the other element are small whole numbers. They come in whole pieces called atoms
Ex. co/co2 - 1 carbon in both, 2 oxygen in the second
* you will never have co1.5 or c02.5, they must be whole number ratios
Dalton's atomic theory-
father of the atom,
no theory is perfect
His theory is very repetitive and is backed by a lot of experimentation
All matter is made up of atoms. -> law of multiple proportions, atoms are indivisible and indestructible -> law of conservation of mass,
All atoms of a given element are identical in mass and properties ->law of multiple proportions
Compounds are formed by a combination of two or more different kinds of atoms in fixed proportions ->law of definite proportions
In a chemical reaction, atoms can only be separated, combined, or rearranged ->law of conservation of mass
Electrons (JJ Thompson)
Cathode ray tube:
Deflection
Come from different materials
Charge to mass ratio
*the light always bends toward the positive deflection coil, he believed what the was seeing was not light but a beam of negatively charged particles because opposites attract
*no matter what material he used for the cathode he would get the same reaction, so within the atom, there must be similar particles inside each atom
*he named these particles electrons
Also created the mass/charge ratio
He also came up with the first atom model called:
The plum pudding model: electrons, positive charge distribution, and no nucleus. He believed the pudding was positive and the electrons inside were negatively charged. He also believed electrons where negative.
Millikan oil drop:
Charged oil droplets
Determined numerical charge of electrons
Allowed for electron mass calculations
Some electrons would attach to the oil droplets making them negative
The center metal plate is positive
The bottom metal plate is negative
He would find how heavy the electrons are, they are extremely light
Rutherfords gold foil:
Alpha particles - are heavy, fast, and positive. He would shoot the bullet at the gold foil assuming it would go straight through. When the alpha particle would hit the nuclei of a gold foil atom, which was not very often, it would bounce back.
* the fact that they didn't run into this problem alot made them think it must be small but heavy, and extremely positive in charge. = describing a nucleus
Deflection
Small and massive
Positive charge
The point of his experiment is that inside the atom there is a small item (nucleus) that is small heavy and positively charged
Modern atomic model:
P+=proton, e- = electrons, n=nuetrons
Electrons weigh alot less than protons and neutrons, and their charge is slightly negative, they are located around the nucleus in the electron cloud
Protons weigh the same as the neutrons are slightly positive and located in the nucleus
The nucleus weight the same as protons, and are neutral in charge (0), and located in the center of the atom
9/20/24
Finding the average Atomic mass
amu=atomic mass unit
Proton = lamu
neutron= lamu
*the mass of an atom is the sum of protons and neutrons
For MG(24) = 80% of all of the atoms are mg(24) 16/20 because 16 out of the 20 isotopes are (24)
m(capital) = the average atomic mass ex. M -m x % + m(2) x %(2) + m(3) x %(3)/100
Once you simplify the problem, only write down 4 digits
Round to the nearest hundreth place
To check your answer, it should be very close to the actual mass of the element on the periodic table ex. (oxygen example on slide) =1595.16+.6796+3.59 = 15.99
Abundance with masses: take actual atomic mass directly from the periodic table
10.0129(x) (x=%) + 1.0093 (100-x)/100, then multiply 10.182 times 100 (cross multiplication) 1081.2=10.0129x +1100.93 - 11.0093x, then move ones that look alike to the other side (x’s on one side, no x’s on the other), then simplify on both sides by adding or subtracting. Then divide by x. You will then put the one with the less abundance with the 0g final answer. The one with more abundance will subtract the OG number from 100 or (100-x).
10/4/24
Electron structure:
Opposites in an electron attract
Electrons will first move away from the nucleus, when they come back the energy will be released and shown in a flash of light
The closer an electron and neutron are to each other, the lower the energy, the stronger the attraction and the atom is more stable
The further an electron and neutron are to each other, the more energy, the weaker the attraction, and the less stable it is
Quantized electron orbits (shells):
Defined by the principal quantum numbers which must be an integer
Ex. 1,2,3 etc.
As the quantum number increases the orbit radius increases
Each orbit holds a maximum of 2n^2 electrons
Lower energy orbits will fill up first
Periodicity-the idea that columns on the periodic table have similar properties
*when they have these similar properties they will have a similar number of valence electrons
Valence electrons- electrons on the outermost shell, that will determine the reactivity level
*Roman numerals can represent each “period” or column of the periodic table
Line spectra: The energy level diagram shows that when moving away from the nucleus the energy will get higher
Ground state v. excited state-
Ground state- electrons in their lowest possible energy
Excited state-higher energy level than the ground state
Relaxation & emission:
Relaxation: When an atom transfers from an excited state energy state to a ground state, by transferring energy to other atoms or through emission
Emission: when the frequency of radiation due to electrons transitioning from a high to low energy state, one of the multiple ways to do that
Subshells & electron configuration:
The shell's names (in electron configuration) go in order of s, p,d, f.
row/shell, where an electron is found
Remember when you are in your d-block row you will lose 1 row
When you are in the f-block row you lose 2 rows
*a full shell of 8 valence electrons means that it is stable
Stabilizing metals:
You move the total amount of electrons to the other side and get rid of the stage and shell name from that previous side
Metals lose electrons and non-metals gain them
When negative ions are added to an atom it gets bigger and when positive ions are added to an atom it gets smaller
Cation-positive ion
Anion-negative ion
Covalent bond-sharing of nonmetal electrons
Monatomic ion has 1 ion
Ionic Bonding-positive and negative ions cancel each other out, it is the idea that a positive and negative ion form a bond and become stuck together because opposites attract
The transfer happens in order to stabilize the atoms
The octet rule: positive metal ions come first and negative nonmetal ions come second
The last three letters of nonmetal ions normally are changed from ium->ide
When you have an uneven amount of electrons that don't add up to zero, you can bring in three or more atoms in order for it to do so
Remember when an atom loses electrons it has a +
When an atom gains electrons it has a -
Chemical Bonds:
The attractive force that holds atoms together within a compound always includes electrons, which will be attracted to their own nucleus, and nucleases of other atoms
Ionic:
Can be represented by a group of ions
Electrons are transferred between atoms to create ions. It means that one atom loses electrons and another atom gains electrons (cation/anion).
The metal (cation) almost always loses electrons and nonmetals (anion) almost always gain electrons
Remember metals are on the left side of the periodic table and non-metals are on the right side of the periodic table
The chemical formula represents the ratio of ions ex. H20, 2 Hydrogen Ions for every 1 Oxygen ion
The bond is a positive charge being attracted to the negative charge of millions and billions of molecules
Covalent bonds:
Can be represented by an individual molecule, not a bunch of atoms
Atoms are close together and overlap and share electron clouds
Singular units called molecules are formed from these bonds
These bonds are formed between 2 nonmetal atoms
Insoluble in water
*if you ever see a metal atom in a formula it WILL be Ionic
Ionic Solids:
Held together by opposite attracting forces (electrostatic force)
Properties:
Composed of a metal and a nonmetal = polyatomic ions
To melt them, it must be thousands of degrees because their bonds are extremely strong
This means they have a high melting and boiling point
With ionic solids, they cannot have like charges because they will repel
Atoms are locked in a hard but brittle lattice
Hard Substances:
resistant to being scratched but can scratch other things
Brittle:
something that will crumble
If their ions get misaligned (like charges) they will fall apart
Conductors:
In solid form, they are poor conductors
This is because in conducting they must have charged particles that are free to move
Since these ions are bonded, they cannot move around
Solubility:
Soluble in water
In a dissolved form they are very good conductors
The water molecules will allow the particles to freely move around
Electrolyte and Conductivity:
Electrolyte is a synonym for an ionic compound
Electrolyte solution contains a substance that when dissolved conducts electricity
Electricity is the flow of electrical current that moves through any substance with mobile charged particles
Dissolved ionic compounds have freely moving ions that can conduct electricity
Covalent Compounds:
Atoms in molecules are held together by covalent bonds
Intermolecular Forceses:
For molecules to stick together you must use Intermolecular Forces (IMF’s)
They allow one molecule to stick to another
It's strong, but its strength doesn’t compare to an Ionic or Covalent bond
They have much weaker strength than other real chemical bonds
Properties:
Softer than ionic compounds and are gases and liquids at room temperature - weak
Low melting and boiling points, mean that it requires a heat of less than 100 degrees to melt it
Poor conductivity because electrons are shared and they are not charged
No circumstance can allow for conductivity to occur with covalent bonds
Nonelectrolyte Solution:
These are compounds that can dissolve in water but do not conduct electricity because the dissolved particles are not charged
Dissolved covalent compounds are non-electrolytes
*pure water is a terrible conductor, but ionic compounds that have broken down in water have become electricity conductor
Metallic Compound:
Metallic is similar to ionic because they have moving charged particles
They also are like covalent bonds because they have shared electrons between all of the atoms
All valence electrons are shared between core cations and delocalized into an electron "sea"
Properties:
Large range of melting points
Group I metals have very low melting points, and most will melt in your hand.
Transition metals, except Mercury, have higher melting points.
Lustrous: Shiny because they have electrons that move to the surface and when light strikes them they become shiny
Ductile and malleable
Ability to move the ions around
Opposite of brittle
Great conductors.
Metals are the only conductors that can conduct in the solid state
Do not dissolve, water cant tear it apart
It's a metal if there are elements from the left side of the table included
Network Covalent Solids:
Are like giant molecules
A network of covalent bonded ATOMS that extends throughout a crystalline structure, holding it firmly together.
Properties:
Hard
Sublime or melt at high temp
Nonconductors
Examples are diamond, graphite, and quartz.
Covalent structures do not dissolve (nonsoluble)
10/21/24
Covalent Bonds:
When nonmetal atoms react with each other to achieve a full octet, they will use shared electrons to form this bond
Pair of electrons shared between 2 atoms
When hydrogen reacts, it does so to form a duet
Single Bond- 2 shared electrons
Double Bond-4 shared electrons
Triple Bond-6 shared electrons
An octet-an atom with 8 valence electrons that is stable and low in energy
It is hard for Hydrogen to get into an octet, its most stable point is a duet
Duet- 2 electrons, specific to Hydrogen
The red number at the top of the periodic table shows the number of valence electrons originally in their shell, on the right, “drop the one”
The hydrogen atom has only 1 valence electron, to make a bond with other electrons, they need 4 atoms to bond
Stable Molecule: when the shell has 8 valence electrons (octet) and each one has a covalent bond
Dot Structure:
Allows to know how many bonds are needed
These dot structures combine to form compounds that achieve the required octet or duet
Lone Pair: non-bonding, already bonded because there are more than 4 valence electrons originally
The distance the element is from the noble gas is the amount of bonds it will make in total, ex. Nitrogen - 3 bonds
The placement of these “dots” around the element does not matter
Atoms in the same columns should always have the same dot structure
The one that can make the most bonds will go in the center of the structure
In the formula, if there are multiple of one element, the element is probably going to be on the outside of the other
Boron is an exception, you can't get an octet only 6
A negative ion gives you an extra electron to use
A positive ion gives you one less electron to use
Carbon always has 4 bonds
Oxygen has 2 bonds
Hydrogen has 1 bond
First, one that can make the most bonds goes in the middle, whatever comes before it will be bonded to it immediately,
Dots v. Lines:
Draw lines to replace dots
1 line is 1 bond
2 lines (equal sign) are 2 bonds
3 lines are 3 bonds
Lewis Structures:
Count the total number of valence electrons for each atom, or group of atoms, in a molecule (e.g., CHCI has 26 electrons).
Identify the center atom (usually the atom present in the smallest quantity or the least electronegative).
Connect your atoms with single, double, or triple lines. Adjust your electron count to determine how many dots to add needed to bring atoms up to their octet or duet.
Hydrogen never has dots
Hydrogen has 1 bond
C, Si, and Ge have 4 bonds
N, P, As, Sb has 3 bonds
O, S, Se, Te have 2 bonds
F, Cl, Br, I, At, have 1 bond
*There are never odd total amounts of electrons
If you have multiple carbons put them all in a row
When you have carbon it is almost always in the middle
Smell:
Organic compounds smell, but 1st they must find a way into your nose
To smell them, they must evaporate (liquid to gas) or sublimation (solid to gas)
The function of Smell:
*functional group Louis structures in one note
A functional group is a cluster of atoms that are found in various molecules
The group tells molecules properties such as smell
More complex molecules can have a mixture of properties
Alkane:
It only has Carbon and Hydrogen
It has single bonds
Ex. C2 H6
Alkene:
Only has Carbon and Hydrogen
1 or more double bonds
Ex. C2 H4
Alkyne:
Has Carbon and Hydrogen
Has 1 or more triple bonds
Ex. C2 H2
Aldehyde:
Has Carbon, Hydrogen, and Oxygen
C and O are always double-bonded on the end and Carbon is also single-bonded to Hydrogen
Ex. C2 H4 O
Ketone:
Has carbon, hydrogen, and oxygen
Minty
Carbon and oxygen are not double-bonded on the end
One double-bonded o
Ex. C3 H6 0
Alcohol:
Has carbon hydrogen and oxygen
Oxygen and Hydrogen are single-bonded together
Ex. C2 H5 0H
Ether:
Has carbon oxygen and hydrogen
No O on the end
Has an O in the middle of two single bonds
Ex. C2 H6 0
Acid/Carboxylic Acid:
Has carbon oxygen and hydrogen
Smells bad
Ex. COOH
Ester:
Has carbon hydrogen and oxygen
COO in the middle
Amine:
Has carbon hydrogen and nitrogen
Smells fishy
Has a Nitrogen with multiple single bonds 2-3
Carboxylic Acid: Smells very pad like stinky feet or rotten milk
Ester Groups: They smell sweet
Ketone Groups: Smells minty
Amine Group: smells fishy
Isomers:
Isomers are compounds that share the same molecular formula, but they are arranged in a different order.
Even though isomers are made from the same atoms, they have unique properties because they often form different functional groups.