STRUCTURE OF AN ATOM

STRUCTURE OF AN ATOM ELECTRON - the NEGATIVE particles surrounding the nucleus of an atom. discovered by JOSEPH JOHN THOMPSON

STRUCTURE OF AN ATOM PROTON – positively charged particle in the nucleus of the atom Discovered by Eugene Goldstein

STRUCTURE OF AN ATOM NEUTRON – a neutral subatomic particle present in the nucleus of an atom Discovered by James Chadwick in 1932

POEM ABOUT THE ATOM I’m Penny the Proton and I’m pretty large, I’ m considered a plus, with my POSITIVE charge. My friends and I, in the nucleus we huddle, It’s nice and cozy with neutrons to cuddle! I’m Ned the Neutron and I’ pretty heavy, I’m fat and lazy and take things steady. You could call me “cheap” I’ve NO CHARGE at all, I really am just a dense, NEUTRAL ball! I’m Elvis the Electron and I’m pretty quick, I fly round the nucleus at a fair old lick! The protons and I, we tend to attract, I’m NEGATIVE you see and that is a fact!

DEVELOPMENT OF THE ATOMIC MODEL

The Greek Model Democritus – Greek philosopher around the year 400 BC He concluded that atom could not be divided into smaller and smaller pieces forever. Eventually, the smallest piece of matter would be found. He used the word “atomos” to describe the smallest possible piece of matter

The Dalton Model John Dalton – English chemist that proposed the first atomic theory in 1803 Points of Dalton’s Atomic Theory 1) All elements are composed of indivisible particles called atoms 2) Atoms of the same element are exactly alike/identical. They are unique and unchangeable. 3) During chemical reactions, there are changes in the way the atoms combine, separate, or regroup. Atoms are neither created nor destroyed. 4) Atoms combine to form compounds. They combine in a definite ratio of small whole numbers.

Dalton’s Atomic Model

Thomson’s Discovery of Electron

The Thomson Model (1904) J.J. Thomson – English scientist who discovered electrons in 1897 Sometimes called the “plum pudding” model, Thomson thought of an atom as being composed of a positively charged material with the negatively charged electrons scattered through it e

Thomson’s Plum Pudding Model

The Rutherford Model Ernest Rutherford – British physicist who, in 1908 proved the atom had a small, dense, positively charged nucleus. Rutherford’s model proposed that an atom is mostly empty space. There is a small, positive nucleus with the negative electrons scattered around the outside edge

Rutherford’s Experiment Over 98% of the _ particles went straight through. About 2% of the _ particles went through but were deflected by large angles About 0.01% of the _ particles bounced off the gold foil

The Bohr Model Niels Bohr – Danish scientist who, in 1913, proposed the “Planetary Model” of the atom Electrons move in definite orbits around the nucleus, like planets moving around the sun. Bohr proposed that each electron moves in a specific energy level Sir James Chadwick discovered the neutron in 1935

Sample Atomic Structure A Helium Atom                         

The Wave/Electron Cloud Model Based on wave mechanics, this model proposed that electrons have no definite path in an atom The probable location of an electron is based on how much energy it has. The more energy an electron has, the farther it is from the nucleus The small positively charged nucleus is surrounded by a large space in which there are enough electrons to make the atom neutral

Electron Cloud Model

Sample Atomic Structure Hydrogen: a proton surrounded by an electron cloud A Hydrogen Atom

Atomic Symbols Atomic Number (Z)  number of unit positive charges Number of Protons = Z Mass Number (A)  total number of protons and neutrons A = number of neutrons + number of protons A = number of neutrons + Z

Atomic Symbols (Nuclide Notation) Also called Element Notation A Symbol Z 35 Cl 17

of diseases in human organs. ISOTOPES are any of two or more forms of a chemical element having the same number of protons (atomic number) in the nucleus having different number of neutrons. Used for PET imaging and myocardial perfusion; investigation of a range of diseases in human organs.

ISOTOPES OF HYDROGEN Nuclear magnetic Hydrogenation of substances Resonance - medicine Hydrogenation of substances radioactive

IONS are atoms or molecules with a net electric charge due to the loss or gain of one or more electrons.                    H+ : a positively charged hydrogen ion H : the hydrogen atom H- : a negatively charged hydrogen ion

References http://dbhs.wvusd.k12.ca.us/AtomicStructure/AtomicStructure.html http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm