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ATOMIC STRUCTURE DO NOW What is a proton, a neutron, and an electron? What is the charge of each? Where are they found in the atom? • A proton, neutron, and an electron are all sub-atomic particles found in atoms. • A proton has a positive charge. • A neutron has a neutral charge, or no charge. • An electron has a negative charge. • Protons and neutrons are found in the nucleus of the atom. • Electrons are found in orbitals around the atom. THE ATOM All matter is composed of tiny particles called Atoms. All atoms are composed of smaller particles: Protons- atomic particles with a positive charge. Neutrons- atomic particles with no charge. Electrons- atomic particles with a negative charge ATOMIC NUMBER The atomic number- depends on the number of protons in a type of element. In an electrically neutral atom, the number or electrons is the same at the number of protons. Number of protons = number of electrons Atomic Number Atomic Mass ATOMIC MASS Atomic mass is based on the number of protons and neutrons in an atom of an element. A certain element has an atomic mass of 16 and an atomic number of 8. The atomic number equals the number of protons in the element’s atoms. To find the number of protons, subtract the atomic number (8) from the atomic mass (16). 16 - 8 8 neutrons DALTON’S THEORY All matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms. J.J. THOMPSON’S THEORY Discovered a negatively charged particle in the atom, that he named the electron. Chocolate Chip Cook Model of the Atom. Positive and negative charges are distributed evenly throughout the atom. LORD RUTHERFORD’S THEORY Gold Foil Experiment: Fired alpha particles at a piece of gold foil. Most particles when through the foil, but about 1 in 10,000 got deflected. The new evidence allowed him to formulate a new atomic model with a central nucleus. He suggested that the dense positive charge was in the center and the negatively charged electrons were being held in place by attractive forces. Remember, opposites attract! NIELS BOHR’S THEORY Bohr refined Rutherford’s model and suggested that the electrons were in orbitals. This is called the “Planetary Model.” WHAT WE KNOW TODAY Electrons are arranged in energy levels or orbitals around the nucleus of an atom. First shell = maximum of two electrons. Second shell = maximum of eight electrons. Third shell = maximum of eight electrons. So how do we know how many electrons are in an atom of a certain element? The number of protons are equal to the number electron. There is an exception….Ions EARLY GREEK THEORIES 400 B.C. - Democritus thought matter could not be divided indefinitely. • This led to the idea of atoms in a void. fire Democritus earth air water • 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. Aristotle • Aristotle was wrong. However, his theory persisted for 2000 years. JOHN DALTON 1800 -Dalton proposed a modern atomic model based on experimentation not on pure reason. • All matter is made of atoms. • Atoms of an element are identical. • Each element has different atoms. • Atoms of different elements combine in constant ratios to form compounds. • Atoms are rearranged in reactions. • His ideas account for the Law of Conservation of Mass THE LAW OF CONSERVATION OF MASS Atoms are neither created nor destroyed The Law of Constant Proportions Atoms in compounds are in fixed ratios…CO2 is a different ration than CO. ERNEST RUTHERFORD (MOVIE: 10 MIN.) Rutherford shot alpha () particles at gold foil. Zinc sulfide screen Thin gold foil Lead block Radioactive substance path of invisible -particles Most particles passed through. So, atoms are mostly empty. Some positive -particles deflected or bounced back! Thus, a “nucleus” is positive & holds most of an atom’s mass. BOHR’S MODEL • Electrons orbit the nucleus in “shells” • Electrons can be bumped up to a higher shell if hit by an electron or a photon of light. There are 2 types of spectra: continuous spectra & line spectra. It’s when electrons fall back down that they release a photon. These jumps down from “shell” to “shell” account for the line spectra seen in gas discharge tubes (through spectroscopes). BOHR - RUTHERFORD DIAGRAMS Putting all this together To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order) Draw protons Draw electrons around in shells He p+ 2 2 n0 Li 3 p+ 4 n0 Li shorthand 3 p+ 2e– 1e– 4 n0 Be B 4 p+ 5 n° O Al 5 p+ 6 n° 13 p+ 14 n° Na 8 2e– 6e– p+ 8 n° 11 2e– 8e– 1e– p+ 12 n° ISOTOPES One of two or more kinds of atoms of the same element that differ from each other in their atomic masses. There are elements whose atoms differ in the number of neutrons. For example there are two kinds of atoms in Neon. Some have 10 neutrons and others have 12 neutrons. Neon with 10 neutrons has a lower atomic mass than Neon with 12 neutrons…THEY ARE BOTH NEON! CARBON ISOTOPES C-12, C-13, and C-14 are all isotopes of the element Carbon. The number 12, 13, and 14 all refer to the atomic mass of atoms. There are still 6 protons in each, however the number of neutrons change. 12 6C 13 6 C 14 6 C HOW IS THE ATOMIC MASS DETERMINED? Naturally occurring europium (Eu) consists of two isotopes with a mass of 151 and 153. Eu -151 has an abundance of 48.03% and Eu-153 has an abundance of 51.97%. What is the atomic mass of europium?