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Atoms Atoms Atoms are the building blocks of matter. “Everything that is something, is made up of atoms.” Elements • A material made from a single type of atom, which cannot be broken down any further. • 90 exist naturally. Molecules • A bonded group of atoms. • Molecules are the smallest identifiable part of a compound that can exist in a stable state on its own. • It has the chemical properties of that compound. Crystals • Have regular shapes and always have the same shape as a result of the way molecules and atoms link together. • Structure is know as a Crystal Lattice. • Examples: Salt, Diamond A regular repeating 3-D pattern Atoms • The smallest particle of an element that still has the properties of that element. • Basic building block of matter. • Everything is made up of atoms. • Are made up of sub-atomic particles Evidence for Atoms • Behavior of Gasses – Pressure • Chemical Combinations – Ratios of ingredients • Radioactivity – Reactions with phosphors Brownian Motion -Jerky movement of particles. X-Ray Crystallography -Size and arrangement of atoms. Atomic Microscopy -Actual images of atoms produced. Structure of Atoms Anatomy of an Atom Nucleus – The central part of an atom made up of Protons and Neutrons. Neutron – Particle found in the nucleus which has No Electrical Charge, and a mass about the same size as a Proton. Proton – Particle in the nucleus, which has a Positive Electrical Charge. Electron – Particle that orbits the nucleus of an atom and has a Negative Electrical Charge. They move more rapidly around the outer areas of the atom. Their arrangement determines the chemical properties of an atom. Atom Structure particle symbol “relative” mass “relative” charge location proton p+ 1 +1 nuclear neutron no 1 0 nuclear electron e- negligible -1 extra nuclear “relative” vs. “absolute” “relative” “absolute” “relative” “absolute” particle mass mass charge charge p+ 1 1.66 x 10-24 g +1 +1.60 x10-19 C no 1 1.66 x 10-24 g 0 0 e- negligible 9.10 x 10-28 g -1 -1.60 x 10-19 C Sub-Subatomic Particles • There are at least 50 fundamental particles. • Leptons, Quarks, Antiquarks, Photons, Gravitons, Bosons, and Gluons. Scientists infer that sub-subatomic particles are present, use machines to detect them, or prove that they have to be there based on the behavior of particles. Atoms • Rutherford – Discovered the nucleus. – Electron orbit the nucleus like planets around the sun. • Bohr – Studied light given off by atoms. – Energy levels • Remember the Aurora Borealis – Photons • Packet of electromagnetic radiation. • Particle-Like bundle of light. various atoms are arranged on The Periodic Table Over 100 various kinds of building blocks exist Elements • There are over 100 different kinds of atoms based on the number of P+, N, e• There are 90 naturally occurring elements, the rest are produced in a lab. • An element is a substance whose atoms all have the same number of Protons or are made of the same atoms. Elements and the Periodic Table • Symbol • Atomic Number – The number of Protons in each atom • Mass Number – The total number of Protons and Neutrons an atom contains. • Number of electrons can be calculated – Every atom has the same number of electrons as Protons. • Number of Neutrons can be calculated – Mass Number minus Atomic Number Looking at an example we find all sorts of information. 6 C Atomic Number Symbol Carbon Atomic Mass 12.0111 Atomic number (a.k.a. proton number) •Indicates the # of p+’s an atom has •Identification Tag of the element example: each and every C atom has 6 p+’s 5 p+’s would make it B 7 p+’s would make it N Symbol •The abbreviated shorthand used to represent a particular atom Rules Atoms are represented by a 1, 2, or in some cases 3 letter Arabic letter code. The 1st letter is always capitalized; the others (if there are any) are always expressed in the lower case. Be careful using symbols Po PO Atomic Mass • Indicates the amount of matter present in an atom Mass = ( # p+) + ( # no) + (# e-) But considering the negligible mass of the electron Mass = ( # + p) +(# o n) Looking back at the original example: 6 C Carbon 12.0111 # p+ no e- charge Example #2 # 47 Ag Silver 107.8682 p+ no e- charge Using the periodic table • Atomic number - unique to each element equal to the number of protons equal to the number of electrons • Atomic weight average weight of all isotopes of that element Isotopes are atoms of the same element with different numbers of neutrons. - Isotopes • Each isotope has a unique number of protons plus neutrons called the mass number. We said . . . Mass number = protons + neutrons various atoms are arranged on The Periodic Table Over 100 various kinds of building blocks exist Protons, Neutrons & Electrons • Protons – in nucleus – 1 amu – +1 charge • Neutrons – in nucleus – 1 amu – 0 charge • Electrons – outside the nucleus – 0 amu – -1 charge Atomic mass unit (amu) - 1 amu = 1.6606 x 10-27 kg Atomic charge - 1 electron = -1.6 x 10-19 Coulombs - 1 proton = +1.6 x 10-19 Coulombs Identifying elements • Atomic number (Z) – the atomic number is equal to the number of protons in the nucleus • Mass number (A) – the mass number is equal to the number of protons plus neutrons (N) in the nucleus A=Z+N Example Problems Sodium Chlorine Nickel Bromine Gold Periodic Table Anatomy • Metals – Reactive Metals – Transition Metals – Poor Metals • • • • • • Metalloids Non-Metals Lanthanides Actinides Groups and Family On-Line Periodic Table Group Number / Family Group 1 – 2, 13 – 18: Main Group Elements Group 1: Alkali Metals Group 2: Alkaline Earth Metals Group 3 – 12: Transition Elements Group 11: Coinage Metals Group 15: Group 16: Group 17: Group 18: Pnictogens Chalcogens Halogens Noble Gases Electron Configuration Electron Orbits • Number of P+ in an atom equals the number of e• Electrons are arranged in orbits or shells around the nucleus • Each orbit can only hold a certain number of electrons. Max e- per orbit: – Orbit 1: 2 e– Orbit 2 on: 8+, Variable Wolfgang Pauli Subshell # of Orbitals s 1 Max # of Electrons 2 p 3 6 d 5 10 f 7 14 Shell Subshells Max Shell Population 1 1s 2 2 2s 2p 8 (2 + 6) 3 3s 3p 3d 18 (2 + 6 + 10) 4 4s 4p 4d 4f 32 (2+6+10+14) Electron Configuration • The arrangement of electrons – Diagram or Numbers • Electron configuration determines how an atom will react with other atoms. – What it can bond with and what type of bond it will form. • Periodic Table Column Numbers – Number of electrons in outer orbit Example Problems Sodium Chlorine Potassium Nickel Bromine Gold Review • Write out the electron configuration for: – Helium – Oxygen – Calcium – Iron – Iodine – Uranium – Radon Shells • Electron shell = Energy Level • Valence Shell – Outermost energy level Lewis Dot Diagrams Atomic Spectra • The most stable state of an atom is when electrons are at their lowest energy levels. • Adding energy to an atom can move an electron up to a higher energy level. • When the atom releases energy, the electron falls back to a stable energy level. The move and the release of the associated energy is emitted as light. • Line emission spectra are like fingerprints of elements. Oxidation Number • Charge that results when electrons are transferred. • Columns on the periodic table • Lewis Structure Ions What holds it together ? • Nuclear forces – strong force - overpowers the electrostatics force to hold the particles together in the nucleus – weak force - involved in beta decay • Binding energy E = mc2 – energy released in building an atom due to the difference in the mass of the atom compared to the mass of the individual particles Radioactivity • The emission of particles or energy (photons) from the nucleus of an atom – Alpha particles () - a He nucleus, they have relatively little penetrating power – Beta particles () - beta negative (electrons) and beta positive (same mass as an electron but opposite sign) have greater penetrating power than – Gamma rays ( ) - high energy electromagnetic waves, similar to light but much higher frequency, have the greatest penetrating power. Nuclear reactions • Fusion - “build up” atomic nuclei releasing the binding energy – require extreme temperature – research in “cold fusion” • Fission - “break apart” atomic nuclei releasing neutrons, beta particles and/or gamma rays – nuclear reactors – nuclear bombs