Properties of the Atom & the Periodic Table Section 1: Structure of the Atom

Scientific Shorthand Elements on the periodic table are represented by symbols. Chemical symbols consist of one capital letter or a capital letter plus one or two lowercase letters. The symbol for silver is Ag. Silver’s Latin name is Argentum. The symbol for gold is Au. Gold’s Latin name is Aurum. Plumbium is lead’s Latin name. Lead’s symbol is Pb. A subscript to the right of a symbol indicates the number of atoms of that particular element present in a compound.

Atomic components—Parts of the atom An atom is the smallest piece of matter that still keeps the properties of the element. The element silver is only silver atoms, uranium atoms are only uranium atoms. Atoms are different from one another because of the number of PROTONS they have. Silver always has 47 protons Uranium always has 92 protons.

The parts . . . The nucleus is the center of the atom. It is made up of: protons, with a positive electrical charge (+), neutrons with a neutral charge (no charge). The electrons are found outside the nucleus in what is called a cloud. Electrons have a negative electrical charge (-). Electrons are approximately 1/10,000 the size of a proton or neutron.

Even smaller parts . . . Smaller particles make up protons and neutrons. These are called quarks. There are six kinds of quarks - up quarks, down quarks, strange quarks, charm quarks, bottom quarks, and top quarks. Their names don't really mean anything, just that they are different kinds of quarks.

More on quarks . . . Quarks were hard to find. Particles had to be accelerated into collisions with great force and speed. The Tevatron at the Fermi Accelerator in Illinois was used for these experiments. It is about 6.4 km in circumference and uses electric and magentic fields to accelerate, focus, and collide particles. Particles are detected using computers and other particles.

More on quarks . . . In order to understand their calculations, physicists assigned the quarks fractional electrical charges of 2/3 and -1/3. Such charges had never been observed before. Quarks are never observed by themselves, and so initially these quarks were regarded as mathematical fiction. Experiments have since convinced physicists that not only do quarks exist, but there are six of them, not three.

Even smaller parts . . . The top quark was discovered last. It is the most massive quark. It had been predicted for a long time but had never been observed successfully until 1995. A team of nearly 450 scientists helped to “find” it.

FermiLab . . . Tevatron Collider was shut down September 30 , 2011

Bubble chambers . . . Old bubble chamber at Fermi Used to capture images of the tracks of subatomic partices after collisions.

Accelerators in history http://en.wikipedia.org/wiki/List_of_accelerators_in_particle_physics

New accelerators Large Hadron Collider: http://www.telegraph.co.uk/science/large-hadron-collider/8675126/Spectacular-images-from-Big-Bang-recreation.html

More A proton is made of two up quarks and a down quark. A neutron is made of two down quarks and an up quark. A force called the strong nuclear force holds the quarks together. Up quarks have a little bit of mass, but most of the mass of a proton comes from the strong nuclear force itself, rather than from the quarks.

Particles names we aren’t going to talk about (much)  Leptons, fermions, muons, neutrinos, hadrons, bosons http://dsc.discovery.com/tv-shows/curiosity/topics/subatomic-particles-in-a-nutshell.htm

Just How small is an atom? https://www.youtube.com/watch?v=yQP4UJhNn0I&feature=player_embedded There are about 5 sextillion atoms in a drop of water. That’s about 5,000,000,000,000,000,000,000 atoms of hydrogen and oxygen.

Using models to understand Models allow you to see something that is either too large or too small, or to envision something that has not yet been built. Scaled-down models The globe The solar system Airplanes Buildings

Using models to understand Scaled-up models Bacteria Other cells Atoms and compounds

Early ideas of atoms Democritus was a Greek philosopher who lived from 480 BC to 370 BC. He created a theory that argued that there are various basic elements which always existed but can be rearranged into many different forms.

Democritus—the Greek Dude Democritus said that matter is made up of small particles Named the parts of matter atomos, which means “uncuttable.” Quote: “By convention there is sweet, by convention there is bitterness, by convention hot and cold, by convention color; but in reality there are only atoms and the void.”

Aristotle argued Another Greek philosopher named Aristotle argued that matter was the same throughout and NOT composed of small particles. He believed that every thing was made of its own type of matter, so, in essence, a table was made of table matter. This idea actually stuck for almost 2,000 years—over Democritus’s idea.

John Dalton Lived 6 September 1766 – 27 July 1844 Was a schoolteacher and scientist in England Looked at Democritus’s ideas and also thought atoms were tiny solid masses that make up matter. Dalton first published his theories on atoms in 1808 in a small book titled A New System of Chemical Philosophy. The book had an enormous influence on the development of both chemistry and physics.

John Dalton’s Atomic Theory Elements are made of tiny particles called atoms. 2. All atoms of a given element are identical. 3. The atoms of a given element are different from those of any other element. 4. Atoms of one element can combine with atoms of other elements to form chemical compounds; a given compound always has the same relative numbers of types of atoms. 5. Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.

J.J. Thomson’s discovery of the negative charge (electron) in 1897 Click here for Thomson's discovery He took Dalton’s “spherical atoms” idea and found that there is a negative charge associated with the particles. He imagined the negative particles to be like the raisins embedded in a plum pudding. I like to compare it to a blob of chocolate chip cookie dough.

Bohr’s model Danish physicist Niels Bohr, 1913 Hypothesized that electrons travel in fixed orbis around the atom’s nucleus In 1911 Ernest Rutherford and his student James Chadwick discovered that the nucleus contained positive protons and neutral neutrons. We use this model today to understand the basic structure of the atom Rutherford's experiment to detect the nucleus

Electron cloud model 1926 An electron cloud is the area around the nucleus of an atom where its electrons are most likely found. The cloud’s diameter is 100,000 times larger than the diameter of the nucleus. Therefore, most of an atom is made up of empty space. It is not a good model to use to understand electron placement and transfers, however.

Electron cloud model 1926

Orbitals of atoms The Electron Cloud Model is alternately called the Atomic Orbital Model. Electrons actually travel more in “orbitals.” Orbitals give a more accurate placement of electrons. Some periodic tables state the electron orbitals. They are shown at the right.

Orbitals of Atoms