Mr. Panico’s Geoscience Course - Odyssey Charter School - Sept. 2012

The Atomic Model and Matter

Students the entire universe is made up of extremely small particles of matter called atoms.
The word atom means indivisible. If an atom is divided then it can no longer be recognized as
matter. Inside an atom are three types of sub-atomic particles: protons, neutrons and electrons.

Protons, Neutrons and Electrons
The proton is a particle that carries a positive electric charge and is arranged in the center of the atom. The center of the atom is called the nucleus. The second type of particle in the nucleus is called the neutron. Neutrons are also arranged in the nucleus and these particles have no electrical charge and hence are neutral.

The 3rd type of sub-atomic particle is called the electron and it is much smaller than the proton or the neutron. The electrons orbit the atom in a large region of space surrounding the nucleus. The electron holds a negative electric charge. We are familiar with electrons in the sense that electrons flow through wires as electricity.

The Atomic Model
Electrons orbit the nucleus at different distances from the nucleus, with the more energetic electrons orbiting further away. If we could make a true-to-scale model of an atom we would see that the nucleus is very small, let’s say the size of a baseball, and the electrons are like the size of raisins spinning around the baseball from a very far distance of around 5 football fields away, or 1,500 ft.

Atoms are made mainly of empty space
You can see that this true scale model shows that there is a tremendous amount of space that comprises atoms and therefore atoms are mainly made of space.

The Number of Protons Determines the Type of Atom
The primary sub-atomic particle is the proton, because the number of protons inside an atom determines which type of atom it is. For example, all atoms that have 8 protons in the nucleus are oxygen atoms. All atoms that have 6 protons are carbon atoms. A better way of saying it is for an atom to be a gold atom it must have 79 protons, no more and no less. If an atom could change its number of protons then it would become a different type of atom. (An atom changing its number of protons does happen in nature and it is called nuclear decay).

94 known types of atoms
There are 94 naturally occurring atoms in the universe that science knows of. These atoms are represented in the Periodic Table. More on this later…


Periodic Table

The Letters Represent the Elements
The letters you see in the periodic table represent the elements. Mercury is Hg. Gold is Au. Stainless steele is made up of several elements so it is not represented in the periodic table. Only pure elements, are in the Periodic chart, not mixtures of several elements.


The Atomic Number = the Number of Protons
The number of protons an atom has is called its Atomic Number. The atomic number of carbon is 6 because carbon atoms have 6 protons. The atomic number of oxygen is 8 because oxygen atoms have 8 protons in their nucleus. The atomic number of gold is 79 because gold atoms have 79 protons.


Here you see copper with the atomic number of 29, because copper atom's have 29 protons in their nucleus.

Atoms are the Pure Chemical Elements
There are 94 naturally occurring atoms in the universe, so that means there are 94 naturally occurring elements. Elements are substances, forms of matter and gasses that are made up of only one type of atom.

When only one type of atom makes up a piece of matter then that matter is referred to as an element. If you held a piece of pure copper element in your hand that means that in the piece of copper contains only copper atoms. So it is a pure piece of copper with no other types of atoms in it. Holding a large sample of a pure element is rare. Most substances large enough to hold will contain other types of atoms mixed in it.

Stainless steel for example has several types of atoms in it so it is not an element but rather a mixture of elements.



         3 protons and 3 electrons

Number of Protons = Number of Electrons = Neutral Charge Atom
Now in most atoms the number of positive proton it has is the same as the number of negative electron it has. So, the carbon atom with 6 protons must have 6 electrons too, in order for it to be a neutral atom. An aluminum atom has 13 protons so it must also have 13 electrons.

Remember the number of protons equals the number of electrons in neutrally charged stable atoms. (There is an exception when an atom is an ion, explained below).

In some Atoms The Number of Neutrons will vary from The Number of Protons. This fact is referred to as Isotopes.
Now in general, the smaller atoms have the same number of neutrons as protons, but that is not the case for all atoms. For example, among carbon atoms, which all has 6 protons, most of the carbon atoms will have 6 neutrons, BUT not all will. Some carbon atoms may have 8 neutrons, though most have 6 neutrons.

In this image Carbon-13 has 7 neutrons and Carbon-14 has 8

Isotopes Refers to Variations in Number of Neutrons within a Type of Atom
Making reference to the fact that any type of atom will have some variations as to the number of neutrons they contain is call isotopes. All carbon atoms must have 6 protons to be a carbon atom. Most carbon atoms will have 6 neutrons as well, but some will have 8 neutrons. These variation in the number of neutrons are isotopes of carbon. A carbon atom with 6 neutrons is an isotope called carbon-12. A carbon atom with 8 neutrons is the isotope called cabaron-14. Isotope Carbon-12 has 6 protons and 6 neutrons, hence Carbon-12. Isotope Carbon-14 has 6 protons and 8 neutrons, hence its name Carbon-14.

19 Protons + 20 Neutrons = Atomic Mass of 39

Atomic Mass (Atomic Weight) is the Number of Protons + Neutrons
Another important concept for scientists is Atomic Mass (also called Atomic Weight). Atomic mass refers to the weight or really the mass of an atom. Each particle in the nucleus equals one unit of mass. So, 12 particles in an atom’s nucleus equals a mass of 12. If an atom has 6 protons and 6 neutrons in its nucleus then the total mass for that atom = 12. A carbon atom has 6 protons and 6 neutrons so its atomic mass = 12..

If an atom has 8 protons and 8 neutrons in its nucleus than that atom has an atomic mass of 16.
The Atomic mass of atoms is simply adding up the protons and neutrons in its nucleus.

But Neutrons Vary in Number (isotopes)
However, in any type of atom there will be some variation as to the number of neutrons so how can we declare the exact atomic mass? Well scientists simply use the average number of neutrons for any type of atom in determining the Atomic Mass. For example, Carbon has 6 protons in generall but really 6.0107 neutrons on the average. So the atomic mass of Carbon is 12.0107. BUT FOR OUR PURPOSES WE CAN ROUND THE ATOMIC MASS TO 12.

Oxygen has 8 protons and 8 electrons. Though most oxygen atoms have 8 neutrons some may have less so overall the neutron number for oxygen is averaged at 7.9994. But for our purposes we can just say 8 neutrons.


Short Video on Atoms and Isotopes:


Please Listen - Great Video on Isotopes - 5 minutes

Symbols on the Periodic Table

The Periodic Table is an organized visual representation of all the information about the 94 types of atoms (that is elements), neatly placed in a table of data. Each atom or element is represented by a symbol that gives the atom’s information.

Here you see the atomic symbol in the Periodic Table for Carbon.
~ Atomic Number is 6 (has 6 protons)
~ Symbol is C (for carbon, duh).
~ Name Carbon.
~ Average Atomic Mass 12.0107. Atomic Mass is protons + neutrons. Most carbon atoms have 6 neutrons but some have more. So the average number of neutrons is 6.0107. So the Atomic Mass is 12.0107. But for our purposes we can just round it down to 12.

Here are some Periodic Tables you can see on the Web. Please view these charts and become familiar with their information.

Simple color: http://go.hrw.com/resources/go_sc/periodic/SSHK1PER.PDF
Color: http://www.ktf-split.hr/periodni/download/en-color100.pdf
Black and white: http://www.ktf-split.hr/periodni/download/en-black.pdf

More on the Periodic Table (heavier, bigger atoms)
The Periodic Table is a chart that shows the increasing number of Protons with Hydrogen (H) on the top left as the first element because it has only 1 proton. Then over to the right is Helium (He) as it has 2 protons. Then back to the left with Lithium (Li) with 3 protons and so on through the chart.

Notice the bigger atoms, that is, the atoms that have many protons and neutrons are organized at the bottom of the chart. These “heavier” elements have more mass, that is, more particles and literally weigh more. They also have many more neutrons than protons. The rule is that in general an atom will have the same number of neutrons as protons mainly applies to the smaller atoms on the first 3 rows of the Periodic Table.

The heavy element Bohrium (Bh) has 107 protons but its atomic mass is 264.   So, 264 - 107 = 157 neutrons on the average for Bohrium atoms. That’s a lot of neutrons and makes the atom more massive. Bohrium and the other heavier atoms definitely have more neutrons in the nucleus than protons.

Matter

When the same types of atoms combine together to make a substance that matter is called an element because it is comprised of only one type of atom. But different elements can combine together to form compounds.

Compounds
Compounds are substances that are formed by two or more types of elements (atoms) combining to create an entirely new substance than the elements that comprise it. For example, the element chlorine (Cl) can combine with the element sodium (Na) and then a new substance, table salt (NaCl), is created. The element oxygen (a gas) can combine with the element hydrogen (also a gas) and then a new substance is created, water (H2O, a liquid).

Two types of bonding of atoms: Ionic and Covalent
When different types of atoms combine (that is, bond to each other) to create a new substance there are two types of bonding of the atoms. One is called ionic bonding and the other is called covalent bonding.

Covalent bonding for water; Outer shells share electrons


Ionic Bonding
Ionic bonding is the positive and negative electrical charges attracting each other (similar to the north and south ends of a magnet attracting each other).

Covalent Bonding
Covalent bonding is the outer most shell of electrons being shared between other atoms outer most shells of electrons. Water molecules are an example of covalent bonding.

Ions are atoms that have gained or lost electrons
An ion is an atom that has lost or gained electrons so that it is no longer a neutrally charged atom. For example, an oxygen atom may gain an electron and become a negatively charge oxygen atom because it now has one more negative electron than it does positive protons.

Or, if an oxygen atom looses an electron then it becomes a positively charged ion because it has more positive protons than it does negative electrons.

Examples of molecules formed with different atoms

Molecules
Molecules are groups of atoms bonded together to create a new type of matter (that is, a compound). Molecules are formed by covalent bonding (sharing outer most electrons). Many but not all substances are created by atoms bonding into molecules.

Ion atoms can combine to create compounds- (Ionic Bonds)
When atoms gain or lose an electron and therefore becomes positively or negatively charged then those atoms can be attracted or bonded to each other. The negatively charged atoms are attracted to the positively charged and vice-versa. So ions can bond by attraction. An example is negatively charged chlorine ions attracted to positively charged sodium ions will combine into table salt.

Ionic bonding creates a lattice (not molecules). Minerals are made of lattice structure.

Ionic bonding does not form molecules, but rather a mineral substance
Covalent bonding forms molecules. Ionic bonding forms minerals. Minerals are a combination of
different types of elements that bond by positive-negative attraction and not by forming molecules.

Lattice Structure (also called Matrix) but not molecules
The structure of ionic bonding is called a lattice or matrix. This is a repetitive structure of atoms that forms substances. Covalent bonding forms molecules that repeat, but ionic bonding forms lattice matrixes that repeat. In both cases you have many different types of substances that are created by atoms bonding together.


Mixtures

A Mixture of substance, no chemical bonding


Mixtures (physical solid pieces)
When different compounds are mixed together you have a mixture. For example, if you took a bag of salt and mixed it with a bag of pepper you would have a mixture of salt and pepper. The important point here is that the salt remains salt and the pepper remains pepper and there is no chemical bonding going on. The two types of matter, salt and pepper, are just mixed together, that’s all. They could be separated.

Solutions are particles in liquids


Particles can be very small in water; solution



Solutions (particles in a liquid)
A solution is when a type of matter is mixed into water. Because water is good at dissolving the substance, the matter ends up being broken down into tiny little pieces that cannot be seen by the eyes.  These tiny pieces are suspended in the water and may be invisible or may give the water a color.

For example, if you took sugar and poured some in a jar of water and stirred the water eventually the sugar particles would seem to disappear, but of course they did not. Instead the sugar just dissolved into such small pieces that you cannot see them any longer. Drink the water and it will be sweet with sugar. This is called a solution.

Four States of Matter
All matter exists in normally 3 states though technically there is a 4th state of matter:
solid, liquid, gaseous and plasma.  Water is a great example of the three states of matter.
Water for example can be ice, a solid, or water, a liquid or vapor in the air, which is a gaseous state.

Solids have molecules close together that keep the matter rigid. Liquids have molecules that are further apart and have more energy and therefore are more flexible or fluid in properties. Gas has molecules that are far apart and are even more energetic, so it has no definite shape and can expand into the atmosphere.

Plasma is a gas that is so hot that the atoms lose some of their electrons, which move freely and separate from the atoms.  This type of matter exists in stars in outer space and on earth in lightning bolts and in laboratories.