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Class Notes

Page history last edited by kevin gortney 10 years, 5 months ago

4/7 Tides

 

 

 

12-14 Activation Energy- the minimum amount of energy required to start a chemical reaction.  Similar to an avalanche, it takes a little bit of energy to start the avalanche.

 

11-4 Covalent Bonding- when atoms share their valence electrons so that they all have 8 electrons in their last shell. Click here to learn more about covalent bonding.

10-27  Ionic Bonding (continued) Magnesium Chloride (MgCl2)

10-26 Ionic Bonding - This type of bonding occurs when one atom gives up it's valence electrons to other atoms so that both atoms have 8 electrons in their last shell.  When sodium gives up it's one valence electron to chlorine, it becomes a positive ion (it has one less electron) and when chlorine receives the electron from sodium, it becomes a negative ion (it has one extra electron).  Remember opposite charges attract like magnets.  It's called Ionic bonding because there are two ions (positive and negative).  Remember to always list the positive ion first, followed by the negative ion when writing the chemical formula.

To learn more about ionic bonding click here.

10-25 Lewis Dot Diagrams- are a way to draw the valence electrons for every atom.

 

10-21 Radioactivity

Radioactivity is when the nucleus of atom throws out particles (either alpha or beta).  Radioactivity occurs for two reasons.  If a nucleus has too many protons (positive charge) then the repulsive force can cause some protons to be expelled from the nucleus as a alpha particle (see diagram below)

 

Another reason some atoms are radioactive, is because mother nature likes symmetry. In this case, she likes the number of protons and neutrons in the nucleus to be the same.  The most abundant form or carbon is carbon-12 (6 protons and 6 neutrons= 12).  Carbon-14 is a radioactive isotope of carbon- it has 6 protons and 8 neutrons (6+8=14).  In order to regain symmetry, one of the neutrons morphs (changes) into a proton while at the same time an electron (beta partilce) is ejected from the nucleus.  Since the carbon has added a proton to it's nucleus, it's atomic number is no longer 6 but is now 7, so it becomes Nitrogen, with 7 protons and 7 neutrons (symmetry at last!!)  see below.

10-19 Noble (inert) Gases Family

To find out more about the inert gases, click here.

 

10-18 Halogent Family

To learn more about the Halogen family, click here.

 

10-15 Oxygen Family

To learn more about the Oxygen family, click here.

 

10/14 -Nitrogen Family

To learn more about the Nitrogen family, click here.

10/13 - Carbon Family


To learn more about the carbon family, click here.

10/12- Boron Family

All the elements in this family have a valence of 3.  To find out more about the Boron Family click here.

 

 

10/8 Transition Metals.

To learn more about the transition metals, click here.

 

10/7 Alkali Earth Metals:

 

 

 

10/6 Alkali Metals:  These elements all have a valence of 1.  This makes them highly reactive since they'll do almost anything to lose that last electron so they their next inner shell (which has 8 electrons) becomes their last shell.

 

10/5 Hydrogen Atom: The element Hydrogen doesn't belong to any group or family.  It's in a family all by itself. Because it has a valence of one, it's on the far left hand side of the periodic table.  With an atomic number of only 1, It's the simplest and lightest of all elements in the periodic table- it's also extremely reactive because it will do anything to get one more valence electron to fill it's only shell (remember the first shell fills at 2!)

Since Hydrogen is the lightest element, it's even lighter than Helium - but unlike helium which has a valence of 2, Hydrogen is explosive/reactive.  The Hindenburg Airship built by Germany used Hydrogen instead of helium since they didn't have any helium.  The Hindenburg eventually exploded because of the hydrogen.

 

10/4 Octet Rule:

 

9/30 Valence Electrons:  An atom's valence electrons refers to the number of electrons occupying the last outermost shell.. 

9/29 Electron Shells:  The maximum number of electron shells (or orbitals/clouds) any atom can have is 7.  Starting with the K shell which is closest to the nucleus and moving outward to the last shell, Q.  The maximum number of electrons that each shell can hold is shown on the diagram below.

 

 

9/28 Isotopes of hydrogen:

 

9/24 Ions and Isotopes:

Normally atoms have the same number of protons (positive) and electrons (negative) so that they cancel each out.  It is possible for an atom to lose or gain electrons, in which case it becomes either a positive ion or negative ion.  If it loses an electron, it's a positive ion (more protons than electrons), if it gains an electron, then it becomes a negative ion (more electrons than protons).  Only electrons can be gained or lost!!

Although an element's number of protons cannot change, the number of neutrons can vary slightly from each atom- see hydrogen below.  Atoms of the same element that have different numbers of neutrons are called isotopes.

 

 

 

9/23 Atomic Number and Atomic Mass Number

The atomic number is the number of protons in the nucleus.  The Atomic Mass number is the sum of protons and neutrons in the nucleus (you have to remember to round this number up or down to the nearest whole number when trying to figure out how many neutrons there are in an atom)

9/16 Liquid Nitrogen Ice Cream:

9/15 Liquid Nitrogen Basics:  Liquid nitrogen boils at -321oF or -196oC which makes it that cold at room temperature as it comes out of the LN2 canister.  This makes it even more dangerous than Dry Ice so DO NOT let it touch you skin or clothing.

9/13 Physical vs Chemical Change - a physical change just changes the appearance of the substance but it's still the same material; for example when ice melts into water, it just changes it physical appearance, it's still H2O (water).

A chemical change is when a completely new and different substance is formed.

9/10 Vaporization and Evaporation - Vaporization or boiling occurs below the surface as well as on the surface of the liquid.  Evaporation occurs only on the surface and is a much slower process because the temperature is usually below the boiling temperature.



9/9 Condensation- is the change in state from a gas to a liquid.  During condensation, the particles in a gas lose enough energy to change back into a liquid.  For example, when the water vapor in the air comes in contact with the cold glass, it loses energy to the glass- enough so that it changes back into liquid.  When enough water molecules condense you can actually begin to see water droplets form on the glass.

9/8 Viscosity - This is a property of liquids and refers to the liquids resistance to flowing.  The more viscous a liquid is (or liquids with a high viscosity) , the slower it flows (like honey).  A liquid's viscosity depends on the size and shape of its particles and the attraction between them.  Increasing temperature usually affects viscosity by decreasing it- maple syrup that is heated, flows more easily than cold maple syrup.

9/7 Crystalline vs. Amorphous Solids.  Crystalline solids have a regular repeating pattern of crystals.  They melt (change of a solid to liquid) at a very specific temperature. Examples are sugar, salt, snow, ice etc.. Amorphous solids on the other hand, the particles are not arranged in a regular repeating pattern (see picture below).  Unlike crystalline solids, amorphous solids do not melt at a specific temperature- but become softer and softer or change into other substances.  Examples of amorphous solids: plastic, rubber, glass, ice cream...

 

9/3 Dry Ice Investigation

Dry Ice is solid carbon dioxide (CO2) ..and is -109oF so it's really cold and must be handled with care or you'll end up with freezer burns... It's called "dry" ice because it sublimates - goes directly from the solid to the gas state without ever getting wet.

9/2 Changes in States of Matter

Sublimation is when a solid goes directly from the solid state to the gas state - bypassing the liquid state completely. Dry Ice is one of the substances that does this very easily- it's called "dry" ice because it never gets wet or turns to liquid- it just basically turns to gas or sublimates.

9/1  States of Matter

Solids: the atoms are vibrate in fixed positions. Have a definite shape & volume, usually hard.

Liquids: the atoms can slide past one another. Have a definite volume but take the shape of their containers.

Gases: the atoms are moving very fast.  No definite shape or volume- they expand or contract to fill the container they are put in.

Plasma: atoms are moving very fast and excited.  Like a gas, they have no definite shape or volume. They give off energy in the form of light or heat.

8/31 Temperature Scales:  Temperature is a measurement of the "average" kinetic energy (KE) or speed of the atoms/molecules.  Just in the same way that a speedometer in a car measures speed, a thermometer measures temperature which is the speed of atoms.  There are 3 different temperature scales which you should be familiar with.  Fahrenheit is what we use here in the United States: Water freezes at 32oF and boils at 212oFWe use Celsius in science (and the rest of the world)- water freezes at 0oC and boils at 100oC - it's elegant and simple (unlike Fahrenheit, but that's because the Fahrenheit scale was based on salt water freezing at 0oF).  Absolute zero is the temperature at which all molecular motion stops.  The Kelvin scale is based on Absolute zero. 

 

 

8/30 Density & Buoyancy How does a submarine sink/dive or rise to the surface?  The submarine has some compartment inside the submarine which it allows water to fill in order to increase it's density so that it sinks..When it wants to surface, it forces compressed air into those compartments which pushes out the water and which makes the submarine's density less than water..so it rises to the surface.  When a submarine dives, it reduces its buoyant force by taking water into its flotation tanks. Once a submarine is down, it rises again by pushing waterback out. The water is pushed out by filling the flotation tanks with air.

The Buoyant force acting on an object in water is equal to the weight of the displaced fluid.

 

8/23 Density- the density of an substance is a measurement of how much mass per given volume it contains.  In other words, it's a measurement of how many atoms (the stuff that makes up everything in the universe) are packed into a given volume.  Styrofoam is not very dense (in other words, it's mostly made up of empty space) whereas lead has a lot more mass per given volume.

Law of conservation of Matter: Matter is neither created or destroyed, it just get's recycled.  In other words, all the matter in the universe was created when the universe was created about 11 billion years ago (with the big bang).  All the matter that is here on Earth has been here for about 5 billion years.  The matter (atoms) that make up your body have been here on Earth for about 5 billion years.  When you die (which you will), the matter that makes up your body will be recycled once again...

8/26 Density Review:  Remember that water has a density of 1g/cm

If you put diet coke and regular coke in a tank full of water- the diet coke floats and the regular coke sinks.  Why?  (regular coke has sugar in it, making it more dense).  The human body's density can vary (much like a submarine) depending on how much air you have in your lungs.  With a lung full of air, the human body has a density less than water and will float,..but if you let most of the air out of your lungs, you will sink to the bottom of the pool.  When people drown, their lungs fill with water- the density of their body increases (greater than water) and they sink to the bottom of the lake.  The coast guard or sheriff will sometimes "drag" the lake to recover the dead body.  Sometimes scuba divers will be brought in to look for drowning victims.  If the body can't be recovered, it will usually float to the surface after a few days due to putrification (decomposition).  The human body bloats with gas as it starts to rot/decompose and eventually it's density changes-becoming less than water, and it floats to the surface.  People who drown at Lake Tahoe are an exception to this- the water is so deep and cold that bodies rarely decompose and float to the surface.

 

 

 

 

 

8/20 Measurements in Science:  Scientists use an expanded metric system called the International System of Units (SI)

Length is measured in meters.

 

Mass, also known as "matter".. (all the "stuff" in the universe) is the amount of matter an object contains measured in kilograms (kg).  1,000 grams = 1 kg  Scientists measure an object's mass using a triple beam balance.

 

Weight is related to Mass but is NOT the same thing.  Weight is the mass multiplied by the force of gravity on the object. 

The mass of an object does not change, but it's weight can depending on the gravity- for example you weigh more on Earth than on the Moon because the Earth's gravity is much stronger.  If I travel to the moon, my mass has not changed, but my weight has changed because the moon's gravity is less.  Weight is measured in Newtons (N) because it's considered a force.

Volume is the amount of space that an object takes up and are measured in cubic meter (m3) or cubic centimeter (cm3).  Volume of liquids or gases is measured using the Liter (L) or milliter (mL).  1 ml = 1 cm3

There are mathematical formulas for finding the volume of common shapes (see your student planner p.9)

To find of volume of an irregular shaped object, you might use a graduated cylinder.  Note the volume before you drop the object in the graduated cylinder, the change is the volume of the object.

 

8/19 Lab Activity: Candle Observation Activity (tape/glue into your science journal) to be graded on Friday when journals are stamped.

8/18 Scientific Observations:  information you gather using your five senses: touch, hearing, sight, smell or taste. Scientists have developed many instruments that can quantify these observations using numbers. Quantitative observations are measurements with numbers (ie. it weighs 200 lbs, it's 2.3 meters tall etc) whereas Qualitative observations are descriptions without numbers (ie. it smells bad, it tastes sour etc.)  So an observation is something that can be made with only the five senses.  An inference is something that involves a decision being made about something you observe- keep in mind that inferences don't always have to be correct, but they should make sense based on your observations.  For more on this, click on this link: observations vs. inferences.  A prediction is a statement about the future based on prior experience: given a set of circumstances a certain outcome is expected.  Weather forecasts are predictions about weather that is expected based on certain factors.

 

Scientific Method:

 

 

 

 

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