Chapter 1: Particles and Forces



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Chapter 6.1: Particles and Forces

p 118


Atoms are made of 3 basic parts: proton, neutron, and electron

All matter in the universe can be constructed using these 3 particleshttp://cdn.instructables.com/fu5/i8g9/gsut1ddb/fu5i8g9gsut1ddb.medium.gif


https://cdn.sparkfun.com/assets/a/6/2/4/4/519fb817ce395fff0a000000.png
Electric Charge – property of matter that comes in two types called positive and negative

Positive/Negative = attract

Positive/Positive = repel

Negative/Negative = repel



Elementary Charge – smallest unit of electric charge that is possible in ordinary matter, represented by the lowercase letter e

+e = + -e = -

+2e = ++ -2e = --

+3e = +++ -3e = ---



P119 Static Electricity

An object is neutral when its total charge is zero

Neutral – a condition where the total positive charge is cancelled by the total negative charges. Matter is neutral most of the time.

Charged – An excess of positive or negative charge

Static Electricity – the buildup of either positive or negative charge; made up of isolated, motionless charges

http://www.flavum.com/picts/static.jpg http://s3.amazonaws.com/uploads.kidzworld.com/article/34249/static2.jpg?1262111951

A tiny imbalance (less than 1 part per million!) of +/- charges causes static electricity. If two neutral objects are rubbed together, the friction often pulls some charge off one object and temporarily puts it on the other.

The forces between electric charges are very strong, that is why charged objects do not stay charged very long.

Walk across carpet on a dry day, your body picks up excess negative charges.

A door knob is neutral, but as you reach for it, your extra negatives repel the doorknob’s negatives, making it slightly positive. Your negative skin is attracted to the positive doorknob. The shock you feel is energy released when your extra negatives jump to the doorknob.

http://www.fplsafetyworld.com/templates/kidskorner/images/static.jpg

http://www.weathergamut.com/wp-content/uploads/2015/08/lightning_diagram.gif

P120 Inside the atom!



http://a3.files.biography.com/image/upload/c_fill,cs_srgb,dpr_1.0,g_face,h_300,q_80,w_300/mte1oda0otcxmzuymdmynzgx.jpg

Electron: 1897 JJ. Thomson discovered that electricity flowing through a gas gave off particles smaller than an atom and it had a negative charge. He named it corpuscles, but eventually it was renamed electrons. Won Nobel Prize in Physics in 1906 for discovery of the electron. He thought atoms were just blobs of matter, and that anything could go through them. (plum pudding theory)

https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/cyclotron_motion_smaller_view.jpg/260px-cyclotron_motion_smaller_view.jpg Cathode Ray/Vacuum Tube

http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford.jpg

Nucleus – 1911 Ernest Rutherford, Hans Geiger, and Ernest Marsden tested Thomson experiment. They shot positively-charged (++) helium ions at extremely thin gold foil. They expected it to go through, but some bounced back at them. Marsden was the person who actually did the experiment; he was Rutherford’s student. Hans Geiger was his teaching partner at Manchester University in England. This experiment proved that atoms were not “blobs of matter” like Thomson thought.

Rutherford had already experimented with shooting particles at gold foil, but asked Marsden to try it again to see if anything bounced back. Marsden set up a screen covered with zinc sulfide (a glow-in-the-dark powder) and if anything bounced back, it would hit the screen and cause a poof of light to bounce off the screen. He did this in the dark, in order to see the glowing puffs. They tried it with other elements, and the same thing happened. Rutherford won Nobel Prize in Chemistry, and was mad, because he considered himself a physicist.

It hit something. They realized that all the mass of a gold atom was concentrated in a tiny, hard core at the center. Nucleus contains 99% of mass. Positively charged proton was discovered to be part of the nucleus, but that was only half of the mass.

Right after the electron was discovered, scientists knew that there also had to be something positive to balance it out. After Rutherford discovered the nucleus, he realized that this must be where the proton was. He invented the word proton.

Neutron – 1932 James Chadwick found another particle in the nucleus with NO Charge and it weighed the same as the proton. Rutherford was actually the first to suggest that there was something neutral in the nucleus, but couldn’t prove it yet.

http://large.stanford.edu/courses/2009/ph204/liu1/images/f2big.gif

Electron – particle with electric charge (-e) found inside an atom, but outside the nucleus

Proton – particle with electric charge (+e) found in nucleus of atoms

Neutron – particle with zero charge found in nucleus of atoms

Nucleus – tiny core at the center of an atom containing most of its mass and all of its positive charge

P121


Protons and neutrons are grouped together in the nucleus, which is at the center of the atom. They are more massive than electrons.

A proton is 1,836 times heavier than an electron.



All atoms have both protons and neutrons in nuclei EXCEPT a simple hydrogen atom, which has 1 proton and 0 neutrons.

http://1.bp.blogspot.com/-fvsoe2divf4/tv8razjqwmi/aaaaaaaabtg/03uvsqfwess/s1600/bha.gif

Electrons define the volume of the atom. They take up the space outside of the nucleus in a region called the “electron cloud.”

The diameter of an atom is really the diameter of the electron cloud.

http://faculty.wcas.northwestern.edu/~infocom/the%20website/graphics/e-clouds.png

The electron cloud is more than 10,000 times larger than the nucleus.



http://1.bp.blogspot.com/-fvsoe2divf4/tv8razjqwmi/aaaaaaaabtg/03uvsqfwess/s1600/bha.gif http://www.sciencebuddies.org/files/2173/3/chem_img009.gif http://www.bubl.org/bublimages/liatom.gif

If an atom were the size of a football stadium, the nucleus would be a pea at the center, while gnats (electrons) buzzed around the stadium. Mostly empty space!

P122 - 4 Forces of Nature Inside Atoms:

1. Electromagnetic Forces – electrons are bound to the nucleus because they are attracted to protons.

Electrons don’t fall or crash into the nucleus because they are moving around (kinetic energy, like Earth orbiting Sun)



2. Strong Nuclear Force – all positively charged protons in nucleus repel each other. So what holds nucleus together?

It is actually called “Strong Nuclear Force” – the strongest force known to science. This force attracts neutrons and protons to each other – preventing the protons from repelling each other.

In every atom heavier than helium, there is at least ONE neutron for every proton in the nucleus.

3. Weak Force – If you leave a single neutron outside the nucleus, the “weak force” will cause it to break down into a proton and electron.

It doesn’t do anything in a stable atom, but plays a part when atoms break apart or decay.



Gravity – force of gravity on atoms is the weakest force of all that acts on them, but it does act on atoms just like any other type of matter.

P123 Atoms of Different Elements:



Atomic Number – the number of PROTONS in the nucleus. Atomic number determines what the element is.

Hydrogen 1 proton 1 electron = zero charge

Helium 2 protons 2

Lithium 3 protons 3

Carbon 6 protons 6

Nitrogen 7 protons 7

Oxygen 8 protons 8

The number of protons and electrons in a COMPLETE atom is always equal!

Now for the strange, the weird, the unstable, the incomplete ATOMS, the exceptions, the stuff about atoms that doesn’t follow the rules:

P124


ISOTOPES – Atoms of the same element that have different numbers of NEUTRONS in the nucleus

Lithium: 3 protons, 3 electrons, but sometimes 3 neutrons, but most of the time 4 neutrons. Called Lithium 6 or Lithium 7. Lithium 7 is naturally occurring and is much more common than Lithium 6, which scientists think came here from other stars.



https://upload.wikimedia.org/wikipedia/en/thumb/2/2d/lithium_chart.png/220px-lithium_chart.png

Carbon is usually 6 protons, 6 electrons, 6 neutrons for a total atomic mass of 12 (6protons+6neutrons)



http://staff.jccc.net/pdecell/chemistry/carbon12.gif

BUT, there is:

Carbon 13 with 6 protons and 7 neutrons

Carbon 14 with 6 protons and 8 neutrons

They are ALL carbon because they all contain 6 protons, but they are different isotopes of carbon.

http://powerhousemuseum.com/ecologic/files/2011/12/carbon-13.jpg http://d1jqu7g1y74ds1.cloudfront.net/wp-content/uploads/2010/10/carbon-14.gif

P125


Radioactivity

https://www.youtube.com/watch?v=ktvTqknDobU

Almost all elements have one or more isotopes that are stable. “Stable” means the nucleus stays together.

The nucleus of an atom becomes unstable if it contains too many or too few NEUTRONS compared to the number of protons.

If the nucleus is unstable, it breaks apart.

Carbon has two stable isotopes: Carbon 12 and Carbon 13. Carbon 14 is radioactive because it has an unstable nucleus. Carbon 14 eventually becomes Nitrogen 14.

It will eventually change into a more stable form. Radioactivity is a process in which the nucleus emits particles or energy as it changes into a more stable isotope. Radioactivity can change one element into a completely different element.

Alpha Decay: a type of radiation where the nucleus ejects two protons and two neutrons (which is the nucleus of helium 4 atom. Alpha radiation is actually fast-moving “Helium” nuclei.

When alpha decay occurs, the atomic NUMBER is reduced by two because two protons are removed, but the atomic MASS is reduced by four because two neutrons are ejected with the two protons.

Example: Uranium 238 goes through alpha decay to become Thorium 234.

http://outreach.atnf.csiro.au/education/senior/cosmicengine/images/sun/alphadecay.gif

Beta Decay: a neutron in the nucleus splits into a proton and an electron. The proton stays in the nucleus, but the electron is ejected and is called beta radiation.

During beta decay, the atomic number increases by 1 because one new proton is created. The mass number stays the same because the atom lost a neutron but gained a proton. https://www.khanacademy.org/science/chemistry/nuclear-chemistry/radioactive-decay/v/types-of-decay



https://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/beta-minus_decay.svg/240px-beta-minus_decay.svg.png http://education.jlab.org/glossary/betadecay.gif

Gamma Decay: This is how the nucleus gets rid of excess energy. The nucleus emits pure energy in the form of gamma rays. The number of protons and neutrons stays the same.

https://www.youtube.com/watch?v=OHNtSne2Uxk
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