atoms and periodic table.notebook - crsd.org

atoms and periodic table.notebook

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March 05, 2012

Mar 211:00 AM

Introduction to chemistryor...............

Things we have to talk about before we can talk about anything

Mar 211:01 AM

In this section of the chapter we are going to learn several important concepts

atomselementsmoleculesionsionic compoundsperiodic table

Mar 211:02 AM

Protonsneutronselectronsbasic atomic structureatomic numbersatomic weightsand bonding of elements and molecules


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March 05, 2012

Mar 211:04 AM

We are going to start by looking at something that is in every high school chemistry book in the world.

The Periodic table

Mar 211:07 AM

Mar 211:09 AM

Did you get all that?


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March 05, 2012

Mar 211:10 AM

Of course you didn't!

For this course, you will NOT have to memorize the periodic table of the elements....you will just have to be able to use the periodic table to understand how substances work together, what they are made of and, how to use the table to get a better understanding of basic chemistry

Mar 211:12 AM

MARCHING DOWN THE ROAD OF THE PERIODIC TABLE....

Mar 211:13 AM

The most important thing to know about the periodic table is that it contains all the known elements arranged in some type of logical order


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March 05, 2012

Mar 211:14 AM

Okay....what is an element?

Mar 211:14 AM

That's hard to define... BUT

since early times people have believed that all substances that are around us are made up of very fundamental, simple "things"

Mar 211:16 AM

fine. But how many of these "things", these "elements" are there?


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March 05, 2012

Mar 211:17 AM

2?

Mar 211:17 AM

5

Mar 211:17 AM

50


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March 05, 2012

Mar 211:17 AM

1,000?

Mar 211:17 AM

What are they?How do we find them?

AND.....

Mar 211:18 AM

Well in our every day lives it is clear that many of the substance around us can be separated into different substances, so they must be compounds

but if you keep trying to break something down into simpler substances and never succeed, maybe that substance is an element.


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March 05, 2012

Mar 211:20 AM

Then how do we really know?

Mar 211:21 AM

WE DON'T

in fact since very recently, there were some compounds that were so stable (resistant to being broken down) that they were believed to be elements for a very long time

Mar 211:22 AM

However we do need a definition for what an element is.

The opperational definition of an element is: "A substance that cannot be broken down into simpler substances by ordinary physical or chemical means"


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March 05, 2012

Mar 211:24 AM

UNDERSTAND?

Mar 211:25 AM

The conceptual definition of an element is: "A substance composed of only one type/kind of atom"

now that's better....

However, you can't see individual atoms... and it won't help you determine the difference between an element or an elephant by using this definition. What this definition does allow you to do is understand the difference between elements like gold, copper and sulfur from water or sugar, which are compounds.

Mar 211:41 AM

The concept of atoms goes back farther than 2,500 years, however it was not until the 1800s that a real understanding of atoms began to be accepted by the scientific community through scientific debate rather than philosophical debate.

in 1869 something wonderful happened....


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March 05, 2012

Mar 211:05 AM

Dmitri Ivanovich Mendeleev

Mar 211:44 AM

began the first true periodic table...which in some ways resembled today's periodic table...but in some ways it was very different. Back then there were only 60 known elements while today there are 118

Mar 211:47 AM

There were several elements "missing"

.....If you don't know something exists, how do you know it is missing?

Mendeleev arranged the atoms from lightest to heaviest, but that doesn't help in determining if an unknown element is missing...


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March 05, 2012

Mar 211:50 AM

Mendeleev also noticed that some elements "behaved" the same way at predictible intervals.

an element reacts violently with water then 8 elements (heavier) away from this atom, another one did the same, then another 8 elements later another one behaved like this as well

for instance...

Mar 211:57 AM

Because of this discovery, Mendeleev further arranged the atoms to groups called families, because just like human families, they have similar characteristics

"found" spaces

Predicted properties of undiscovered atoms to they would be easier to find in the labratory

Mar 212:00 PM

But atoms are not the most fundamental parts of matter. We now know that the atom is composed of much smaller particles called

PROTONSNEUTRONSELECTRONS


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March 05, 2012

Mar 212:02 PM

Each element on the periodic table is represented by a symbol, and this symbol is compose of one or two letters (Carbon = C) (Oxygen = O)

Mar 212:06 PM

Mar 212:08 PM

atomic number

1. How many protons are contained in the nucleus of that atom of that element

2. Tells you how many electrons are surrounding the nucleus of the atom


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March 05, 2012

Mar 212:13 PM

Mar 212:15 PM

Protons are one of the fundamental particles of an atom and are said to have a positive charge, or a charge of "+1"

Are you thinking...."plus 1 what?" GOOD!

Mar 212:18 PM

electrical charge.

and...electrical charges come in discrete units (at least when discussing protons and electrons) which means that you can never have a fraction of a charge, they will always be whole integers

The smallest unit of charge is the charge on one proton, the next smallest possible charge would be twice that...there is no fraction of a charge in between those.


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March 05, 2012

Mar 212:22 PM

But atoms are electrically neutral. ALL atoms in their natural state are electrically neutral so what does that mean?

Mar 212:24 PM

we say that there are only two kinds of charges, which we have arbitrarily labeled as being +1 and 1. We could have just as easily called them Sammy and Joey, if we wished. We label them +1 and 1 because these were the only 2 different kinds of charges we have found, and in addition, if we combine 1 of each of these 2 different kinds of charges the result is no charge at all. If we assume that opposite charges attract and like charges repel, what kind of experimental result would force us to conclude that there were, in fact, 3 different kinds of charges in nature instead of only 2?

Mar 311:29 AM

If we could charge 3 different spheres and then found that any combination of 2 would attract each other, then we would have to conclude that there were 3 different kinds of charges instead of only 2. In reality it is impossible to charge 3 spheres without 1 combination repelling each other which indicates that there are only 2 different kinds of charges


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March 05, 2012

Mar 211:55 AM

In our last discussion, we learned that the atomic number is an important number. It tells you the number of PROTONS in the atom. We also learned that an atom will NEVER change how many protons it contains without changing it's identity, or the type of element it is.

In other words....

Mar 37:42 AM

The number of protons DEFINES what kind of element a substance is.

We also learned that all atoms, in their natural state, are electrically neutral. This means that they do not have a positive or negative charge. Because of this, you can determine the number of electrons in a neutral atom by looking at the atomic number as well.

Mar 37:45 AM

There are many difference between a proton and an electron....

1. The most obvious one is their charge: Protons have a positive charge while electrons have a negative charge


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March 05, 2012

Mar 37:54 AM

2. The second is their location: Protons are found in the nucleus of an atom while electrons are found outside the nucleus, zipping around in energy "fields" called orbitals

Mar 37:55 AM

3. The third is their size: Protons are "large" (at least compared to an electron) while electrons are "teenyweenie"

Mar 38:24 AM

4. The fourth, and for this discussion, the most important difference is this:the number of protons in an atom of a particular element will never change, while an atom can gain and lose electrons without changing what kind of element it is.

BUT IT WILL DO SOMETHING TO THE ATOM....


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March 05, 2012

Mar 38:28 AM

The gain or loss of electron(s) in an atom will change the charge of the atom

Mar 38:38 AM

An atom can gain or lose electrons to form charged particles called IONS

Atoms that gain electrons become negatively charged and are called anions

Atoms that lose electrons become positively charged and are called cations

The charge of an ion is written in the upper right of the chemical symbol, like S or Al

Mar 38:45 AM

Let's look at our chlorine atom from the last discussion......

Cl

If we wanted to indicate that this chlorine atom had gained an electron, what would we do?

How many electrons would it have? How do you know?


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March 05, 2012

Mar 38:55 AM

Let's practice a bit.

NaKCaAlSn

+

+

2+

3+

4+

Using your periodic table and the information next to the chemical symbols, determine the number of electrons for each cation

Mar 39:02 AM

time for a joke!

One day there was a horribly depressed and anxious sodium atom. Her friend came up to her and said "what's wrong, Sodium you look horrible!" Sodium stopped sobbing for a second and said "I'm afraid I have lost one of my electrons!" Her friend said "Oh no! That's awful! Are you sure?""Oh yes." Said Sodium "I'm positive!"

Mar 39:07 AM

Now let's ask another question......

Is there any simple way to know what a given atom will do will it gain or lose electrons, and if so how many will it gain or lose?

For most atoms on a practical level, the answer is not really. But for some atoms like sodium and chlorine you can make a pretty good educated guess about what they are likely to do. And you do this my knowing something MORE about our periodic table


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March 05, 2012

Mar 39:11 AM

The periodic table is organized according many characteristics of certain elements.

The atomic number of the elements (how many protons are in the nucleus) is represented as increasing by 1 as you look from left and move to the right of the table

Mar 39:13 AM

Mar 39:13 AM


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March 05, 2012

Mar 39:21 AM

The vertical columns are called families or groups

(atoms that have similar characteristics)

The horizontal rows are called rows or periods

The zigzag staircase line near the right hand side of the periodic table divides the elements into metals on the left and nonmetals on the right

Mar 39:26 AM

Mar 39:26 AM

IT IS THIS LINE THAT HELPS YOU TO UNDERSTAND IF AN ATOM IS LIKELY TO GAIN OR LOSE ELECTRONS AND GENERALLY HOW MANY ELECTRONS AN ATOM/ELEMENT IS LIKELY TO GAIN OR LOSE


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March 05, 2012

Mar 311:34 AM

Metals share some properties, as do nonmetals

Metals:

found to the left of the stair step line most are solid at room temperature have few electrons in their outer orbital good conductors of heat and electricity shiny

likely to form positive ions

Mar 312:01 PM

found to the right of the stair step line more than half are gasses at room temperature most have an almost complete outer orbital of electrons brittle and likely to shatter when hit with a hammer poor conductors of heat and electricity

Nonmetals:

likely to form negative ions

Mar 412:31 PM

The number of electrons in an atom is determined by the number of protons. This is determined by looking at the atomic number.


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March 05, 2012

Mar 412:33 PM

But you might be wondering....how are these electrons distributed around the nucleus?....

Mar 412:33 PM

Are you wondering that?

Mar 412:34 PM

GOOD!


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March 05, 2012

Mar 412:34 PM

Well.....it has been determined that electrons whip crazily around a nucleus like so many frenzied bees in discrete levels, called orbitals, clouds, energy levels, and all kinds of other completely random and incorrect terms.

Mar 412:35 PM

The really interesting thing is that electrons are not evenly distributed in these orbitals, there are different numbers of electrons in every level, and every level has to be filled until a new level can be "made"

Mar 412:36 PM

Now we know that atoms are neutral, but what would you think if I told you that they usually are not STABLE?


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March 05, 2012

Mar 412:37 PM

Stable?

Mar 412:37 PM

whattheheckdoesthatmean??????

Mar 412:38 PM

Welllllllllllllll................

Stability (at least in an atom) means that the outter layer also known as the valence electron shell is full.


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March 05, 2012

Mar 412:38 PM

WOWIEZOWIE!

Mar 39:41 AM

???????What is this number and what does it represent?

Mar 39:43 AM

Tells us how heavy an atom of that element is compared to atoms of all the other elements

It's called the atomic weight or atomic mass

So now I hope you are wondering....How the heck is that number determined? And why is it a fraction if we are dealing with whole particles such as protons, neutrons and electrons


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March 05, 2012

Mar 310:03 AM

Believe it or not this was one of the most complex questions facing chemists in the 19th century, and it well over 50 years to solve it.

It has to do with a particle that is present in the nucleus most atoms, it is called an Neutron. And, like the name implies, it carries no charge at all

Mar 310:11 AM

Particle Charge

Proton +Electron Neutron 0

Mar 310:13 AM

Mass of these particles:

proton 1.673 x 10 27

0.000000000000000000000000001673 kg

Neutron 1.675 x 10

Electron 9.109 x 10

27

31

kg

kg


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March 05, 2012

Mar 310:47 AM

But these numbers are ridiculous. SO we use a different unit for mass, this unit is designed to accommodate the very small amount of mass in a subatomic particle. It is called the ATOMIC MASS UNIT or the AMU

Mar 310:49 AM

The mass of the particles represents in AMU

Protons 1.0073 AMUNeutrons 1.0087 AMUElectrons 0.00055 AMU

Mar 310:54 AM

The atomic mass tells you the average mass of all of the atoms of a certain element. This is calculated by particles in the nucleus of the atom.

What are the particles that are found in the nucleus?


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March 05, 2012

Mar 311:01 AM

good

Mar 310:56 AM

So why the decimal?

Can you have a fraction of a subatomic particle?

Mar 310:57 AM

So why the decimal?


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March 05, 2012

Mar 31:23 PM

Mar 311:14 AM

Because atoms can have differing amounts of neutrons in it's nucleus. Sometimes an atom will have more than is average, sometimes an atom will have less neutrons than average

An atom that has more neutrons than is average will, quite obviously, be heavier

An atom that has fewer neutrons than is average will, quite obviously, be lighter

Mar 311:01 AM

Because atoms can have differing amounts of neutrons in it's nucleus. Sometimes an atom will have more than is average, sometimes an atom will have less neutrons than averageHOWEVER,If you average ALLLLLLL the atoms of a single type of element, their average mass (that including heavy and light atoms) is indicated in the atomic mass


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March 05, 2012

Mar 311:03 AM

Let's look at chlorine again.

# of protons

Average number of protons and neutrons in the nucleus

What does this number say about what the atom is likely to have when it comes to neutrons?

Mar 311:18 AM

Right!This type of element typically produces heavier atoms.

Mar 39:50 AM

Here's a helpful rule when determining the atomic mass of an element. You will need to round to 1 decimal point. Here's an example

S15.9994 32.064O

Oxygen Sulfur


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March 05, 2012

Mar 39:56 AM

This tells us that an average sulfur atom is almost twice as heave as the average oxygen atom. If we look at Helium (He) we can determine that it's atomic mass is 4.002, which will round to 4.0

What we find when we look at this is that Helium is about 1/4 as heavy as an average oxygen atom and about 1/8th as heavy as an average sulfur atom

Mar 39:59 AM

Not all atoms can be compared so nicely...

If we compare our good 'ole chlorine to oxygen we get something like this

35.516.0 = 2.22 to 1 or just over 2

times heavier than an oxygen atom

Mar 39:41 AM

An atom that has fewer or more neutrons than is average is called an

Isotope


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March 05, 2012

Mar 39:32 AM

DIHYDROGENMONOXIDE

Sep 1712:35 PM

atoms and periodic table.notebook - crsd.org

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