ATOMIC STRUCTURE

All atoms are made of the same things ƒ Electrons: particles with negative charge ƒ Protons: particles with positive charge ƒ Neutrons: particles with no charge ƒ Quarks: building blocks of protons and neutrons ♦ 2 UP quarks + 1 DOWN quark = 1 PROTON ♦ 2 DOWN quarks + 1 UP quark = 1 NEUTRON ƒ Only difference between an atom of carbon and an atom of hydrogen is the number of these particles

Structure 1) Nucleus ¾ Center of atom ¾ Heaviest part of atom ¾ Where you'd find the protons and neutrons ¾ Neutrons act as the glue that keeps the protons together in the nucleus 2) Electrons ¾ Very small compared to the size of protons and neutrons ¾ Spinning around the nucleus ¾ Electrons also spin up or spin down ¾ Electrons like to be in pairs—one up, one down 3) Shells ¾ Electrons travel in shells ¾ An atom can have up to seven shells ¾ First shell is closest to nucleus; it is called shell K ¾ First shell can hold only TWO electrons and NEVER MORE ¾ Second shell can hold eight electrons; it is called shell L ¾ The carbon atom has two electrons in shell K, and only has four electrons in the second shell (shell L) for a total of six electrons ¾ An atom can have several more shells (M-Q), each with a maximum number of electrons being 2n2 where n=the number of shells. Example: the third shell can have up to 2(32) = 2(9) = 18. (See more on this in the section entitled: Calculating the number of electrons in each shell.) 4) Balance ¾ Negative charges (ELECTRONS) and positive charges (PROTONS) have to be in balance or in equal number or else the atom will disintegrate. ¾ If an atom has one or more extra electrons, or has lost one or more electrons, it is considered an ion. ¾ If an atom has an unstable nucleus due to an imbalance of protons or neutrons, it is considered radioactive.

Electron Shells Electrons move around the nucleus of an atom in shells. There are some simple rules about these shells. These are: ƒ The first shell will hold up to two electrons. The first shell is called shell K. ƒ The second shell will hold up to eight electrons. The second shell is called shell L. ƒ The later shells will hold more than eight electrons, but they often stick at eight. (Shells M-Q) ƒ Eight electrons in the outer shell make an atom very stable.

Chemistry Handout 1 Created by Diane Speed ATOMIC STRUCTURE

Electron Shells

Electrons are arranged around the nucleus in SHELLS. For simplicity they can be thought of like mini-planets orbiting a central sun, but it is closer to the truth to think of them as "clouds" of electric charge around the nucleus.

Calculating the Number of Electons in Each Shell The shells are numbered outward from the Nucleus. The maximum number of electrons found in each shell can be calculated by: where "n" is the number of the shell. Maximum Number Shell of Electrons in the Number Shell 1 2 x 1 = 2 2 2 x 4 = 8 3 2 x 9 = 18 4 2 x 16 = 32 5 2 x 25 = 50 6 2 x 36 = 72 7 2 x 49 = 98

The Octet Rule: In general, atoms are most stable when they have 8 electrons in their outer-most shell. (Octet means 8.) The exception is the first shell which is most stable with TWO electrons.

Why do electron shells matter? ƒ Atoms have to be touching before they can react. This makes the outer shell of electrons very important, because that is where the atoms touch. ƒ If there are eight electrons in the outer shell the atom is stable. This means that the atom won't react even if it is touching another atom. ƒ Neon is a very stable gas! ƒ If there are just a few more or less than eight electrons in the outer shell, the atom is likely to react.

Chemistry Handout 2 Created by Diane Speed ATOMIC STRUCTURE

ƒ Sodium has one electron in the outer shell and chlorine has seven. If sodium loses an electron and chlorine gains one, both atoms become stable. This is how sodium chloride or salt is made.

Periodic Table ¾ The periodic table lists all know elements from lightest to heaviest ¾ There are 112 known elements. Some are man-made and do not occur in nature. ¾ Groups ƒ Columns ƒ All elements in each group have the same number of electrons in their outer shells and therefore have similar chemical properties. ¾ Periods ƒ Rows ƒ The element’s atomic number increases by one from one element to the next going across the row from left to right. ƒ Elements grouped in periods will have the same number of electron shells. For example, the elements in the first period or row have one shell. The elements in the fifth period or row have electrons in five shells. ¾ Information listed for each element ƒ Element’s name ƒ Element’s symbol: usually an abbreviation of its Latin name, e.g. silver’s abbreviation is Ag because in Latin silver is argentum, gold is Au because gold in Latin is aurum ƒ Atomic number: the number of protons in one atom. It is usually the case that the element will also have the same number of electrons. ƒ Atomic weight ¾ Hydrogen atom ƒ simplest atom ƒ one electron and one proton ƒ atomic number: 1 ¾ Carbon atom ƒ six electrons, six neutrons, six protons ƒ Atomic number: 6 ƒ All living things on Earth are carbon-based. ƒ The study of carbon-based chemistry is called organic chemistry.

Reading Electron Shells Using the Periodic Table

Explanation of electron shell configuration. For more details, go to: http://www.corrosionsource.com/handbook/periodic/e_shells.htm

Suggestion: while reading this explanation, please refer to a periodic table.

As atomic number increases so too does the number of electrons in a neutral atom of the element. The valence electrons are largely responsible for its chemical behavior. If elements having the same number of valence electrons are grouped together the elements in each group or family will have similar chemical properties.

The first short period contains only two elements. These elements fill the K shell. It ends with helium which contains a full K shell consisting of two electrons.

The second short period contains eight elements beginning with lithium and ending with neon. Neon has a complete L shell of eight electrons.

Chemistry Handout 3 Created by Diane Speed ATOMIC STRUCTURE

The third short period contains eight elements beginning with sodium. It ends with argon, which contains eight electrons in the M shell.

The fourth period contains eighteen elements beginning with potassium. It includes a series of elements from scandium through copper. These elements are known as transition elements.

They are building the M shell from eight to eighteen electrons. Before this series begins though two electrons enter the outermost N shell. After the series the N shell then builds up to eight electrons ending with krypton.

The fifth period is just like the fourth period in which the O shell takes two electrons then the N shell builds to eighteen electrons before the O shell continues out to eight electrons ending with xenon.

The sixth period contains 32 elements. It too has a transition series beginning with lanthanum and ending with gold, in which the O shell fills to eighteen electrons.

Note however that this series is split after lanthanum with a series of fourteen elements. In these elements the N shell (third from the outside) is filling from eighteen to 32 electrons. These are referred to as the inner transition series, lanthanum series or the rare earth elements. It begins with cerium and ends with lutetium.

Following lutetium the transition series from hafnium to gold completes by building the O shell to eighteen electrons. The outer P shell then continues to build to eight electrons ending with radon.

The seventh period is incomplete. The first two elements, francium and radium fill the Q shell with two electrons. Then the P and O shells fill in the same way as the sixth period. This produces the actinide series.

How Shells Fill For a visual explanation of just how the shells fill, go to: http://lectureonline.cl.msu.edu/~mmp/period/electron.htm

This exercise demonstrates that shells don’t always fill one shell at time. It also makes the point that electrons like to be in pairs.

Chemistry Handout 4 Created by Diane Speed ATOMIC STRUCTURE

Links: Access some of these links to find out more about atomic structure.

Explanations of atomic structure http://www.visionlearning.com/library/module_viewer.php?mid=51

Moving simulations of first 11 elements in the periodic table For further details, the table linked below shows the electron configurations of the first 11 elements. Atomic structure animation table http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-atoms.shtml

Early days (19th/20th century) of atomic theory http://www.visionlearning.com/library/module_viewer.php?mid=50

The illustration linked below compares the two simplest atoms, hydrogen and helium. Simulated hydrogen and helium atoms http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-atoms.shtml

Atom Builder. Have your child build an atom. Teaches the concepts behind subatomic particles and why charges need to be balanced. http://www.pbs.org/wgbh/aso/tryit/atom/

A comic view of the elements in the periodic table http://www.privatehand.com/flash/elements.html

Chemistry Handout 5 Created by Diane Speed ATOMIC STRUCTURE

Another way to view shells, first proposed by Buckminster Fuller. http://www.buckminster.info/Ideas/06-VE-UltraMicroPC-ElectronShell.htm

SELECTED IDEAS OF BUCKMINSTER FULLER AN IMPROVED MODEL OF ELECTRON SHELLS In 1966 and 1978 the sculptor, Kenneth Snelson, patented an improved way of modeling the various electron shells. His models reflect nature's geometry as discovered by R. Buckminster Fuller.

Snelson's models demonstrate that there are at least seven possible geometric shapes that the local electron orbits can take.

Chemistry Handout 6 Created by Diane Speed