Two-step Dimensional Analysis For a conversion where you are going from a prefix to a prefix (example pg to ng) you have to pass through the base unit, basically ending up multiplying the given value by two fractions: 1 to go to the base unit, one to go to the desired unit.. Ex. 56 µg = ________________pg

 10 − 6 g  x 56 µg X   1µg   

 1 pg  56 x10 −6 x1 pg  −12  = 1x10 −12  10 g  =

56 x10 −6 pg 10 −12

This is actually a very powerful tool for any chemistry or physics course as it allows you to easily convert units. I have seen grade 10 kids who have a heck of a time when they get to the matric for science and they do not know how to manipulate units. My goal is to give the students tools to make it easier for them later on. The upside for the students in grade 7 is that this is about the most math there is in the course. After this, the material is more qualitative. To show you a more fun example of the power of dimensional analysis, I showed the kids how to calculate their age in seconds, just making sure to keep canceling out the units properly: 12 years x

365days 24hrs 60 min 60s x x x = 378 432 000 s 1 year 1day 1hr 1 min

Can go backwards: how many years in 2000 000 seconds. How many Km in 5000 inches, given 1 inch = 2.54 cm, etc….

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Matter Matter is anything that has mass (that can be weighed) and takes up space. Therefore, anything around you is matter, including the air you breathe!

Organization of matter:

Matter

↓ (are made up of…) Complex molecules (ex. DNA)

↓ Simple Molecules (ex. Sugar)

↓ Elements (ex. Carbon, Hydrogen, Oxygen, …)

↓ Atoms

↓ Protons (p+), neutrons (n0), and electrons (e-)

Elements are naturally or man made substances that cannot be created by combining any two other things on earth. They are pure substances. Information about them can be found on the periodic table of the elements. (Note: you need to know the names and symbols of the atoms identified in class with a star on your periodic table) Atoms are the basic unit of matter. They are the smallest part of the element that still retains properties of that element. You can think of elements as “sand” and atoms as the “grains of sand”. Elements are made up of many of the same type of atom.

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The Periodic Table of the Elements Dmitri Mendeleev created the first periodic table of the elements. He showed that when the elements were ordered according to atomic weight, a pattern resulted where similar properties for elements recurred periodically. Based on this, the periodic table was reorganized on the basis of increasing atomic number rather than on atomic weight. The revised table could be used to predict the properties of elements that had yet to be discovered. Elements in the periodic table are arranged in Periods (rows) and Groups or Families (columns). Elements within a group share several common properties.

Group 1: Alkali Metals The alkali metals are located in Group IA (first column) of the periodic table. Sodium and potassium are examples of these elements. Alkali metals form salts and many other compounds. Group 2: Alkaline Earth Metals The alkaline earths are located in Group IIA (second column) of the periodic table. Calcium and magnesium are examples of alkaline earths. They are the most abundant elements on earth. Group 17: Halogens The halogens are located in Group VIIA of the periodic table. Examples of halogens are chlorine and iodine. You find these elements in bleaches, disinfectants, and salts. They are also quite colorful. Group 18: Noble Gases/Inert Gases The noble gases are located in Group VIII of the periodic table. Helium and neon are examples of noble gases. These elements are used to make lighted signs, refrigerants, and lasers. The noble gases are not reactive. 3

Reading the periodic table of the elements Each block of the periodic table houses an element, along with a few standard facts about that element: Atomic number: integer equal to the number of protons or electrons in the element. Gold's atomic number is 79.

Element symbol: one or two letters. In the case of two letters, the first one is always capitalized. Hydrogen's symbol is just H, while helium's is He. Symbols can be tricky because some are based on the first letter(s) of the element's common name, as hydrogen's is, while other symbols are based on the Latin names of the element, such as Au for gold (or aurum in Latin). Element name Atomic weight: usually a decimal value, such as 196.966 569(4) for gold

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Structure of the atom The atom is made up of 3 main particles: Protons, neutrons and electrons. Their respective properties are shown on the table below. Particle

Abbreviation

Charge

Mass (in a.m.u.)

Location in the atom

Proton

p+

+1

1

Nucleus

1

Nucleus

Neutron

n0

0

Electron

e-

-1

almost zero

Orbiting the nucleus

The Atom:

Nucleus Protons and neutrons

Electrons orbiting the nucleus

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Finding the particles in the atom How many protons, electrons and neutrons are in an atom of krypton, carbon, oxygen, neon, silver, gold, etc...? To find the number of protons, electrons and neutrons in an atom, just follow these easy steps:

Step 1 - Gather Information The first thing you will need to do is find some information about your element. Go to the Periodic Table of Elements and click on your element. If it makes things easier, you can select your element from an alphabetical listing. Use the Table of Elements to find your element's atomic number and atomic weight. The atomic number is the number located in the upper left corner and the atomic weight is the number located on the bottom, as in this example for krypton:

Step 2 - The Number of Protons is... The atomic number is the number of protons in an atom of an element. In our example, krypton's atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus. The interesting thing here is that every atom of krypton contains 36 protons. If an atom doesn't have 36 protons, it can't be an atom of krypton. Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of krypton creates an atom of bromine.

Step 3 - The Number of Electrons is... By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.

Step 4 - The Number of Neutrons is... The atomic weight is basically a measurement of the total number of particles in an atom's nucleus. In reality, it isn't that clean cut. All you really need to find is something called the mass number. Unfortunately, the mass number isn't listed on the Table of Elements. Happily, to find the mass number, all you need to do is round the 6

atomic weight to the nearest whole number. In our example, krypton's mass number is 84 since its atomic weight, 83.80, rounds up to 84. The mass number is a count of the number of particles in an atom's nucleus. Remember that the nucleus is made up of protons and neutrons. So, if we want, we can write: Atomic weight = (Number of Protons) + (Number of Neutrons) For krypton, this equation becomes: 84 = (Number of Protons) + (Number of Neutrons) 84 = 36 + (Number of Neutrons) What number added to 36 makes 84? Hopefully, you said 48. That is the number of neutrons in an

In Summary... For any element: Number of Protons = Atomic Number Number of Electrons = Number of Protons = Atomic Number Number of Neutrons = Mass Number - Atomic Number

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