Notes chapter three

The periodic table shows all of the known elements.  Remember an element is the simplest substance.  It cannot be broken down by physical OR chemical means. The elements are named by a single letter or by two letters.  If two letters, the first is always Capitalized and the second is always lower case.  For example Co is cobalt (element) and CO is carbon monoxide (compound)  The elements are named by the properties, countries, people, universities, etc.

PERIODS, ROWS, OR SERIES: Run horizontal

GROUPS  OR FAMILIES: Run vertical

REGIONS OF THE PERIODIC TABLE: Check out the following periodic table so you can identify the regions of the periodic table

INTERACTIVE PERIODIC TABLE    HERE IS ANOTHER INTERACTIVE PERIODIC TABLE THAT HAS THE PICTURES OF THE ELEMENTS

METALS

1.) Good conductors of heat and electricity
2.) have luster
3.) are malleable, bendable and ductile

NONMETALS

1.) Poor conductors or nonconductors
2.) are dull
3.) are brittle

METALLOIDS OR SEMI-METALS

1.) have properties of both but the most important is that they are semiconductors.  This property is perfect for delicate electrical operations. 

NOBLE GASES

1.) Do not react or only react with great difficulty with other elements. 

2.) DALTON'S THEORY:

Dalton proposed the following in the early 1800;s

1.) All matter is made up of atoms.

2.) Atoms of the same element are alike , atoms of different elements are different.

3.) Atoms of different elements combine in simple, whole number ratios to form chemical compounds.

4.) In a chemical reaction, atoms are not created or destroyed, only rearranged.

Most of this remained true but some was later proved to be false.

LAW OF CONSERVATION OF MASS (Antoine Lavoisier, 1785)

In ordinary chemical reactions the mass of the reactants = the mass of the products. IMPLICATION: Atoms are not subdivided.

LAW OF DEFINITE PROPORTIONS: (Joseph Proust, 1797)

In a given compound, the relative number and kinds of atoms are constant. For example in water (H₂0) there is 2 parts H for every one part of 0. also the mass is proportional 2/18 are hydrogen and 16/18 is oxygen (check periodic table for atomic masses) IMPLICATION: The parts of a compound combine in a fixed ratio (unlike a mixture)

LAW OF MULTIPLE PROPORTIONS: The ratio of mass on one element that combine with a constant mass of another element can be expressed in small whole numbers. IMPLICATION: You cannot have 1/2 of an atom

H₂0 for every 1 gram of hydrogen there are 8 grams of oxygen
H₂0₂ for every 1 gram of hydrogen there are 16 grams of oxygen
16grams/8 grams =2 atoms of oxygen.

Example problem one

Example problem two

ATOMIC MODELS

Indirect Evidence: Finding out how something works without really seeing or directly touching the object.

This is the type of evidence that we need to have to really understand the structure of the atom since we cannot really see or touch the atom.

1.) THE GREEK MODEL:

Democritus: First described more than 200o years ago that all matter is made up of atoms. That is if you take a block of gold and keep cutting it apart sooner or later there must be a smallest piece of gold that still has the properties of gold that is no longer divisible. This smallest piece he called the atom which means indivisible.

THOMSON'S MODEL

In 1897 J.J. Thomson proved that the atom was made up of smaller particles. He experimented with a cathode ray tubes

A cathode ray tube is an evacuated tube (has no air) with both sides connected to an electric current. An element was put on one end of the tube and a voltage was given to the tube. Thomson noticed that the element gave off a "ray" This ray was attracted to a positive plate and repelled by a negative plate. He called these negatively charge particles "corpuscles."Here is a summary site for Thomson's experiment . With this new information Thomson developed the Plum Pudding Model of the atom. This model said that

1.) The atom is made up of a positively charge charged material with negatives embedded throughout the structure

Thomson was also able to calculate the charge to mass ratio for an electron by doing the following
1.) He placed magnetic and electric fields in the path of the electron. 
2.) by balancing the two fields he was able to make the electron travel in a straight line.
3.) He found that the charge/mass ratio for an electron was 1.76 x 10¹¹ C/Kg
4.) Need to find the mass to find the charge or the charge to find the mass!

MILLIKANS FAMOUS OIL DROP EXPERIMENT (1912) 

1.) sprayed oil droplets in ionized air inside an electric field.  The oil droplets would pick up electrons from the air.
2.) increased the electric field until the drop floated
3.) At this time the downward force of gravity (w=mg) was counterbalanced by the upward force of the electric force (which is the strength of the electric field x the charge on the drop)
4.) if there was a higher charge on the drop do to many electrons the electric field that was applied was low and vice versa
5.) When he read his field and calculated the charge he found that they never fell below a certain minimum value and all charges were whole number multiples of the minimum charge. 
6.) He found that the minimum charge was 1.6 x 10^-19 C
7.) using Thomsons charge to mass ratio of 1.76 x 10¹¹ C/Kg he was able to determine the mass of an electron
8.) the mass of an electron was calculated to be 9.1 x 10^-31 Kg

PROTON:

1.) Found in a similar fashion as the electron
2.) Steam went from positive to negative
3.) Was not deflected by a magnetic field (too massive)
4.) Carries EQUAL charge as an electron but opposite sign.
5.) The number of protons of the atoms of a given element is always the same and is characteristic of that element
6.) The mass was calculated to be 1.67 x 10^-27 Kg (1836 times that of an electron)

NEUTRON:

1.) Discovered by Chadwick
2.) Has basically the same mass as a proton but has no charge

RUTHERFORD MODEL

In 1911, Earnest Rutherford performed the following experiment. (here are two other simulation of the same experiment. )

Questions:

1.) Rutherford thought most of the alpha particles would go through the gold foil. Explain why.

2.) How did Rutherford explain the deflections of the alpha particles?

Conclusions made by Rutherford

1.) The atom has a very small (about 1/20,000 the size of the atom) nucleus. The nucleus is positively charged and very dense.

2.) The negatively charged particles (electrons) were scattered around the edge of the atom

3.) Most of the atom is empty space.

4.) Problem with Rutherford that according to classical physics a charged particle in motion such as around the nucleus would continuously lose energy and thus spiral into the nucleus. orbits decay and the electrons would fall into the nucleus?

Electromagnetic Spectrum:  To understand the following models we need to first understand a little bit about the structure of light.

1.) Look at you handout on the electromagnetic spectrum.  Many of these types of light you are familiar with. Light is made up of electric and magnetic fields that are acting at right angles to each other.
2.) Notice that the visible spectrum is a very small portion of the total spectrum.  400 nm to 700 nm. Here is a picture of us looking at visible part of the spectrum
3.) The speed of all light waves in air is 3.0 x 10⁸ m/s and is designated by a small c
4.) Frequency is the cycles per second is designated by Hz which is 1/s.  
5.) The period is the time for one complete cycle and is designated by T which is seconds.  The period and frequency are reciprocals of each other.  In other words if it takes 2 seconds to make a cycle then the frequency is 1/2 cycle per second.
6.) Wavelength is normally the distance between two adjacent crests or troughs.  For light it is changes in the electromagnetic fields of the waves
7.)Amplitude in is the height of the wave and for light it is the intensity of the wave.
8.) speed = wavelength x frequency.  Remember speed is constant at 3.0 x 10⁸ m/s.

Is a light a wave or particle: Demonstrate with laser and sound waves. 
Diffraction: How a wave travels around an object or through a slit.
Refraction: How a wave bends when it travels through two different mediums such as air and water. 
Reflection: bouncing off a surface such as a mirror.
ripple wave intereference

WHICH OF THE ABOVE ARE WAVE AND WHICH PARTICLE PROPERTIES?

Youngs experiment: Prove light was a wave by famous two slit experiment showing diffraction pattern of light. Hold fingers together up to light to show diffraction patterns.

The photoelectric effect and Plank's constant: Had the light/particle question really been answered had been answered?

Planks Constant

a.) calculated the smallest amount of Energy allowed. 
b.) found the E =hf where E = energy, h = planks constant 6.63 x 10^-34 J-s and f is the frequency in Hz.

Photoelectric effect
1.) When light shines on certain metals it causes an electric current to be produced.
2.) The photoelectric effect is independent of intensity.  This means if a certain wavelength of light does not cause the effect to occur it will not occur not matter how bright the light is.  This is evidence of a particle nature of light.
3.) The effect is dependent on frequency. That is only light of a certain frequency will cause the effect.  If this frequency is not present no effect will happen.
4.) The energy of the photon is calculated by E =hf 

Summary of light

1.) Light consists of tiny packets of energy called photons.
2.) light of a particular wavelength has a definite frequency, a characteristic color, and a definite amount of energy.
3.) Energy and frequency are directly proportional
4.) Energy and wavelength are indirectly proportional.
5.) Photons have only certain energies, each atom has its own characteristic energy possibilities.  Energy is not continuously released from the atom.

BOHR MODEL

Electromagnetic spectrum of the certain elements

Read through the following link to discover how the Bohr model was developed.

Conclusions made by Bohr:

1.) Electrons move in definite orbits around the nucleus like planets around the sun

2.) The orbits are located at specific distances from the nucleus

3.) When electrons gain energy they move out to a farther orbit.

4.) When electrons lose energy the move into a closer orbit and emit energy in the form of light.

5.) The negatively charged electrons are held in orbit by the positively charged nucleus.

6.) Bohr disregarded that the electron would behave as a classical particle and would not continuously emit energy but rather only when if changed orbits. This flew in the face of classical physics and is one reason that it was not thought of before.

7.) Bohr's model explained the spectral lines that were produced by Hydrogen but did not always translate to other elements with more electrons.

Structure of light and how it is related to the Modern view of the atom.
Kinds of spectra

Class examples
Element tubes under high voltage
Salts of elements labs.

De Broglie: If a wave can have particle properties (light behaves as a particle when it is reflected, etc) then why can't a particle act like a wave?  Wavelength = planks constant/(mass)(velocity)  

Particle properties of light: reflection, rectilinear propagtion, (traveling in a straight line without spreading out) 

Wave properties: diffraction, interference, slower speed in water than air Young's double slit experiment with red light

As small particles are accelerated at high speeds they take on "wave" like properties.
Standing wave demo of an electron

WAVE MODEL:

Bohr's model worked well for some simple atoms but not for more complex atoms. However, The important part of Bohr's work was that when electrons made transitions from energy levels the energy change was "quantized". That is there was a smallest amount of energy that could be transferred at one time. planks constant  E= hf where h is 6.64 x 10-34 J-s and f is the frequency., Also remember the wavelength is equal to c/f where c = 3.0 x108 m/s

The wave model says that

1.) electrons are not found in definite orbits but rather in regions around the nucleus.

2.) it is impossible to know both the exact momentum or position of an electron. (Heisenberg uncertainty principle) To observe the path of an electron you need to interfere with the electron.  Since you interfere with the electron you now have change if from its original path.

3.) electrons have a dual wave and particle properties. classic two slit interference demonstration

4.) Schrödinger's Atom Schrodingers Cat problem

STRUCTURE OF THE ATOM

Read through the following to get a description of the main parts of the atom.

Subatomic particles (particles smaller than the nucleus)

Atomic Number:: number of protons

Isotopes: Atoms of the same element with different masses. (Dalton thought all atoms of the same element had the same mass. This proved to not be true. Think of people. We all are human beings but we have different weights.)

Atomic weight: average weight of the isotopes of an element. For example there are three isotopes of Hydrogen.  Hydrogen 1, hydrogen 2 and hydrogen 3.  Each one of these has one proton because they are hydrogen.  However, H1 has no neutrons, H2 has 1 neutron, and H3 has 2 neutrons.

Mass number: Number of protons and neutrons in an individual atom.

Calculating the number of protons, neutrons, and electrons for an atom.

Number of protons = atomic number

In an atom, the number of protons are also equal to the number of electrons. (why?)

Number of neutrons = mass number - atomic number (since electrons are basically considered to have no mass)

Here is a site where you can review a few problems involving finding these numbers.

Take this Atomic structure quiz

ELECTRON SHELLS

Even though electrons do not travel in distinct orbits we classify "regions" of where electrons can be found as Energy levels, sublevels, and orbitals.

The energy level tells you were you are most likely to find an electron at a given time. Higher energy level values mean the electrons are father from the nucleus. Each energy level may have a smaller number of sublevels and within each sublevel are orbitals.

The first energy level has room for 2 electrons, the second has room for 8, and the third energy level can hold 18. Look at your periodic table and notice that there are two elements in ROW one, 8 elements in ROW two, and 18 elements in ROW three. Can you see how the elements in the periodic table follow this pattern? 

QUANTUM NUMBERS: Describe the best we can the location of the electron in an atom

s orbital can contain 2 electrons, p orbital can contain 6 electrons, d orbital 10 electrons, and f orbitals 14 electrons

Pauli exclusion principle: No two electrons can have the same four set of quantum numbers. (it would mean they are in the same place at the same time)

Orbital diagrams and electron configurations. (AUFBAU Principle)  Look on page 97 of the Holt book and follow the directions in class.  Don't forget about Hunds rule which states that orbitals of equal energy are each occupied by one electron before any paring of electrons occur. Also they will have the same spin. electrons paired in an orbital will have opposite spins. Here is a great diagram with some examples to help you write electron configurations with just the aid of your periodic table. In certain cases, transition elements will fill the s before the d. This is mainly if they can half fill  or fill the d shell.

Take this electron shell quiz

What keeps it all together?

FOUR FUNDAMENTAL FORCES

1.) Gravitational forces: Anything that has a mass has a gravitational field around it. Remember since this particle are very small the have very weak gravitational fields. Also remember gravity can only pull NOT PUSH.

2.) Electromagnetic forces ( Positive or negative charges) Like charges repel and opposite attract. Since electrons are negative and protons are positive they will attract one another. Two protons will repel each other since they have like charges. 1 positive has the same strength as on negative. 2 positives have twice the strength as 1 positive.

3.) Strong force: In the nucleus are all of the protons.. Protons have a positive charge and thus want to repel. The nucleus is very small and thus this force of repulsion is very strong. Why doesn't the nucleus fly apart? The strong force is the "glue" that holds these protons together in the nucleus. This energy is some of the energy released when you split an atom. Therefore even though it acts over a small distance it is the greatest of all of the forces.

4.) Weak force: This force is involved in radioactive decay. The weak force is involved with transforming a neutron into a proton and an electron. This is also called beta decay.

Is there one unified force? This is what physicists are working one now. Even though all of the above forces seem very different, is there a way that they are all related by one unifying concept? Stay tuned to see how this turns out.