Scientific Measurements

Measurements

- the process of estimating or determining the magnitude of a quantity, such as length or mass, relative to a unit of measurement, such as metre or kilogram.

Units of Measurements

- Definite magnitude of a physical quantity, defined and adopted by convention and/or by law that is used as a standard for measurement of the same physical quantity.

SI BASE UNIT

1) Meter for length 

2) Kilogram for mass 

3) Second for time 

4) Kelvin for temperature 

Calibration

- Comparison between measurements - one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device.

Accuracy

  - The degree of closeness of measurements

- Correctness, Exactitude, Exactness, truth

Precision

- The state or quality of being precise; exactness.

Place Values

 for whole numbers:

PRACTICE HERE: http://www.aaamath.com/plc41ax3.htm

for decimals:

 PRACTICE HERE: http://www.aaamath.com/plc51bx2.htm#pgtp

Quantum Numbers

Quantum Numbers

In quantum numbers always use the last electron
configuration in knowing the element`s “n, l, mL, mS”
♥ n- principal quantum
♥ l- azimuthal quantum
♥ mL- magnetic quantum
♥ms- magnetic spin quantum
For example:
6C : 1s2 2s2 2p6
12

Note: We'll be using Carbon as our example

♥ n- describes the energy level, an electron is located in.

Example: 2p6
               n= 2

♥ l- Sublevels in the atoms of the knownelements are s- p- d - f .
♥ describes the shape of the orbital.

Example: 2p6
               l= 1

Why 1?, because in the chart it shows that if the sublevel is p its 1.
















♥ mL-describes the orientation in space for the orbital.

Example: 2p6
               mL- 0

Take Note!!

♥ mS- Describes the spin of an electron.

Example: 2p6
               l= +1/2

Why +1/2?, because if the last arrow Is arrow down its –1/2 because it is
spinning counterclockwise, if its arrow up its +1/2 because it spins clockwise.

Electron Distribution

Electron distribution mnemonics


-The orbital names s, p, d, and f stand for names given to groups of lines in the spectra(plural of spectrum-The distribution of energy, arranged in order of wavelengths). These line groups are called sharp, principal, diffuse, and fundamental.

-A function which gives the number of electrons per unit volume of phase space.
Electron Configuration

-arrangement of electrons of an atom, a molecule, or other physical structure. It concerns the way electrons can be distributed in the orbitals of the given system (atomic or molecular for instance).

Energy levels

-An atom consists of electrons orbiting around a nucleus. However,the electrons cannot choose any orbit they wish. They are restricted to orbits with only certain energies. Electrons can jump from one energy level to another, but they can never have orbits with energies other than the allowed energy levels.



-can only take on certain discrete values of energy, as opposed to classical particles, which can have any energy.



Bigger orbit =higher energy



Energy levels are said to be degenerate, if the same energy level is shared by more than one quantum mechanical state. They are then called degenerate energy levels.

Videos

Energy level

http://www.youtube.com/watch?v=Y9HgalWNCbI



Shell

-The main energy level in which an electron resides. It is given by the principle quantum no. , which is denoted by “n”. “n” can have a positive integral (quantized).

Subshell

-This is the sub-energy level in which the electron resides. It is given by the azimuthal quantum number, denoted by “L”, satisfies the inequality.



Orbital

This is an orientation a subshell takes up in presence of an external magnetic field. It is given by the magnetic quantum number “m”.


Electron distribution mnemonics


-The orbital names s, p, d, and f stand for names given to groups of lines in the spectra(plural of spectrum-The distribution of energy, arranged in order of wavelengths). These line groups are called sharp, principal, diffuse, and fundamental.

-A function which gives the number of electrons per unit volume of phase space.





Electron Configuration

-arrangement of electrons of an atom, a molecule, or other physical structure. It concerns the way electrons can be distributed in the orbitals of the given system (atomic or molecular for instance).





Energy levels

-An atom consists of electrons orbiting around a nucleus. However,the electrons cannot choose any orbit they wish. They are restricted to orbits with only certain energies. Electrons can jump from one energy level to another, but they can never have orbits with energies other than the allowed energy levels.



-can only take on certain discrete values of energy, as opposed to classical particles, which can have any energy.



Bigger orbit =higher energy



Energy levels are said to be degenerate, if the same energy level is shared by more than one quantum mechanical state. They are then called degenerate energy levels.



Videos

Energy level

http://www.youtube.com/watch?v=Y9HgalWNCbI



Shell

-The main energy level in which an electron resides. It is given by the principle quantum no. , which is denoted by “n”. “n” can have a positive integral (quantized).



Subshell

-This is the sub-energy level in which the electron resides. It is given by the azimuthal quantum number, denoted by “L”, satisfies the inequality.


Subshell label L Max.electrons Shells containing it. Historical name

S 0 2 Every shell Sharp

P 1 6 2nd shell + Principle

D 2 10 3rd shell+ Diffuse

F 3 14 4th shell + Fundemental

Atoms

ATOMS

→ the smallest mediaeval unit of time, equal to fifteen ninety-fourths of a second.

→ a theoretical particle of matter, imagined to be incapable of further division; the smallest possible unit of substance.

Sub-atomic Particles:

Protons:

→ a positively charged subatomic particle forming part of the nucleus of an atom → determines the atomic number of an element.

Electron:

→ the subatomic particle having a negative charge

→ orbiting the nucleus; the flow of electrons in a conductor constitutes electricity.

Neutron:

→ subatomic particle forming part of the nucleus of an atom

→ no charge.

How to Determine the Atomic and Mass Number:

• Atomic Number

→ number of protons in the nucleus of an atom determines an element's atomic number

• Mass Number

→ determined by the number of protons and neutrons in an atom

Ex:

* Isotope - Any of two or more atoms of an element having the same number of protons, but a different number of neutrons in its nucleus. (same atomic number but not mass number)

Ex:

IONS

→ an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge

• Anion – gains electrons (negative)

Ex:

• Cation - loses electrons (positive)

Ex:

AZPEN*

Formula:

• A (mass number) = P + N

• Z (atomic number) = P

• P (proton) = Z

• E (electrons) = P - [charge of ion]

• N (neutron) = A - Z

Accuracy, Precision and Sensitivity in Measuring Devices

Accuracy
Imagine hitting a bullseye for more than once and you see the darts are close to the center but they’re not necessarily close to each other. That pertains to accuracy. If your results are near the exact value needed, then they are accurate. The different results don’t have to be near each other. According to qualitydigest.com, no measurement is perfect and all measurements have some error associated with them.

*Let's take a look at this image. This is a good example of accuracy and precision. Since the darts are in the center, they are accurate. and since the results are near each other, they are precise.   
 Precision
Let’s try to go back to our imagination of a bullseye. What if you try to hit it again for four times and the results were not that close to the center but each result is near each other or the same? It means that your results are precise. Precision is the ability to have very close results with repeated experiments. 

Let’s get to the big question.  WHAT’S THE DIFFERENCE?
Accuracy and Precision are a bit the same but there’s also a big difference. When we speak of accuracy, we always try to get the right answer. If you have a number of results and one or maybe two of them are near the exact needed value, then you are accurate. The different results don’t have to be near each other, they just have to be near the correct answer. On the other hand, Precision refers to the nearness of the results to each other, and not necessarily on the correct answer.


Accuracy and Sensitivity in Measuring Devices
Since we already know about Accuracy, we will only discuss the meaning of sensitivity and its use in measuring. Sensitivity is known as the place value that is no longer represented or seen in the calibration. It is also the place value after the accuracy; it is already estimated or approximated. 

Let's look at this image. There are calibrations, right? But what if the liquid that is inside this beaker goes in between those calibrations? how can we measure them?  
Let's imagine a liquid that measures above 100 mL but below 125 mL. We can have an estimation of 110 mL. The accurate part of the measurement is 100 mL because we already know that it is above 100 mL. We estimated the 10 mL of the measurement because we only know that it is below 125 mL. The 10 mL part of our measurement is what we call the sensitivity of the measurement.

What's a percentage error? How do we do that?

Now, every time we take measurements in our experiments, we always measure it more than once. Now, we have to take note if our results are either accurate, precise or simply both. But how do we do that? 
In order to determine accuracy and precision, we must first get the percentage errors of the results. Percentage errors are used to determine how close to the true values, or how accurate experimental values are.

According to gmasononline.com, this is how we get the percentage error.

We really hope you learned some stuff here, so we made some exercises for you. DON'T LOOK UP!

1. Accuracy :________  , Precision : group of values near each other

                        a. estimated value                       b. far from the correct value

                        c. near correct value                   d. Bias

________2. True or False. Sensitivity refers to the estimated part of the measurements.

________3. Gerard, Renzo and Inno recorded the temperature of a boiling liquid three times.

                       Gerard's Result - 78 C

                       Renzo's Result - 79 C                   Correct value - 79 C

                       Inno's Result - 78.5 C

                       Were the results accurate, precise, or both?

_______4.   What is percentage error?

Box Configuration

Aufbau Principle

The physical and chemical properties of elements is determined by the atomic structure. The atomic structure is, in turn, determined by the electrons and which shells, subshells and orbitals they reside in. The rules af placing electrons within shells is known as the Aufbau principle. These rules are:

 1. Electrons are placed in the lowest energetically available subshell.

 2. An orbital can hold at most 2 electrons.

 3. If two or more energetically equivalent orbitals are available (e.g., p, d etc.) then electrons should be spread out before they are paired up (Hund's rule).

Hund's rule

 

In an orbital, electrons will fill all available positions of the same value of s before the opposite spin value appears.
 

Pauli's Exclusion

No two electrons in an atom can have identical quantum numbers. This is an example of a general principle which applies not only to electrons but also to other particles of half-integer spin (fermions). It does not apply to particles of integer spin (bosons).