Atomic Structure and the Periodic Table www.astro.virginia.edu

All Matter is Made of Atoms Hydrogen is the most common atom of our universe Types of atoms in Earth’s Crust Iron 5%, Aluminum 8%, Silicon 28%, Oxygen 47%, Other 12% Types of atoms in Humans Nitrogen 3%, Hydrogen 10%, Oxygen 61%, Other 26 % www.earthshope.org bubblingbrain.wordpress.com

Names and Symbols of Elements Each element has its own symbol Some elements use the first letter of the name: hydrogen (H), Sulfur (S),Carbon (C) Other elements use the first letter of the name plus another letter: aluminum (Al), Platinum (Pt), Zinc (Zn) The first letter is always capitalized and the following letters are lower case.

400 B.C. Early Greek Philosophers determined that atoms are the building blocks of matter.

John Dalton (1766–1844) John Dalton’s theory of the atom started out as a solid sphere with no charges Proposed the atomic theory by investigating atomic weights of atoms

1898-1903 J.J. Thomson determines that an atom is made up of negative electrons embedded in a sea of positive charges . + - www.ucl.ac.uk

1911 Ernest Rutherford did some experiments with thin metal foils and found that the positive charge is located within a central nucleus www.scientific-web.com

1913 Neils Bohr worked under Rutherford but found problems with his theory. He ultimately determined that Electrons are in circular orbits with increasing energy levels. _ _ nobelprize.org

The modern atomic model shows that electrons occupy regions of space whose shape is described by complex mathematical equations. (James Chadwick) www.csmate.colostate.edu

History of Atomic Theory John Dalton’s theory of the atom started out as a solid sphere with no charges. Then J.J. Thomson figured out there were positive and negative charges in an atom. Rutherford determined that the positive charges (protons) were located in the center of the atom and the negative charges (electrons) were scattered around the nucleus Bohr’s theory said that the protons are in the middle and the electrons travel in specific energy levels and orbits around the nucleus Modern model- protons and neutrons in nucleus, electrons on energy levels

Review An atom is made up of protons (+), neutrons (no charge), and electrons(-). The protons and neutrons are found in the nucleus There has to be an equal number of protons and electrons because atoms have no net charge! Atomic mass is the number of protons and neutrons Atomic number is the number of protons (which is the same as the number of electrons) www.csmate.colostate.edu

Vocabulary Atom: the smallest particle of an element that has the chemical properties of the element Nucleus: found in the center of the atom and contains the protons and neutrons Proton: a positively charged particle found in the nucleus of an atom Neutrons: an uncharged particle found in the nucleus of an atom Electron: negatively charged particles that move around outside the nucleus of the atom Isotopes: atoms of the same element that have a different number of neutrons. Chlorine atoms have 17 protons, but some atoms of chlorine have 18 or 20 neutrons these atoms are the isotopes of chlorine

Atoms form Ions Ions: formed when an atom loses or gains one or more electrons(- or + charge) Cation: formed when an atom loses an electron (+ charge) Anion: formed when an atom gains an electron (-charge)

Elements are organized by similarity Modern Periodic Table organized by the atomic # of the elements Dmitri Mendeleev began organizing elements by their physical and chemical properties (1860’s) www.cartage.org.lb

Periodic Table of the Elements Mendeleev produced the first periodic table Called the periodic table because a periodic, or repeating pattern of properties of the elements spiff.rit.edu

Periodic Table Period: each row of the periodic table is called a period. If you read from left to right one proton and one electron are added from one element to the next Group/Family: Each column of the table is called a group or family. Elements in a group share similar properties. Groups/Families are read from top to bottom www.chem4kids.com

Atomic Size on the Periodic Table Left to right atomic size decreases Top to bottom atomic size increases encarta.msn.com

More Properties of Periodic Table www.cartage.org.lb

Periodic Table has distinct regions Reactive: indicates how likely an element is to undergo a chemical change Most elements are somewhat reactive and combine with other materials The most reactive are in groups (up/down) 1 and 17 The least reactive are in group (up/down) 18

Elements combine by the outside electrons All of the electrons in the combining elements do not interact with each other to form compounds…. Valence Electrons: Only the electrons in the element’s outside energy level interact with each other. The most stable configuration has 8 electrons in the outer energy level. Elements in group 1 have 1 electron in outside energy level and elements in group 17 have 7 electrons in outside energy level so they react with each other easily to form compounds and fulfill the 8 electron stable configuration.

Metals Most elements are metals Metals are elements that conduct electricity and heat, have shiny appearance, and can be shaped by pounding (malleability), bending, or being drawn into a thin wire (ductility)

Metal types Reactive metals: Group (up/down) 1 most reactive Transition Metals: Group 3-12 (up/down) generally less reactive than most metals

Rare Earth Elements www.riken.jp Top row of the two rows of metals that are outside of the main periodic table Also known as Lanthanides because they follow the element lanthanum (La) on the table Scientists once thought these metals were available only in tiny amounts on the Earth

Actinide bottom row of the two rows of metals that are outside of the main periodic table The Actinide series is all radioactive and some are not found in nature. www.chem4kids.com

Nonmetals Nonmetals: the elements on the right side of the periodic table Many are gases at room temperature, dull surfaces on the solid nonmetals, cannot be shaped by ductility or malleability

Halogens Elements in group 17 7 valence electrons Greek “forming salts Very reactive non-metals that easily form compounds with metals. These compounds are known as salts. www.chem4kids.com

Noble Gases Group 18 on the periodic table 8 valence electrons Noble or inert because they almost never react with other elements www.chem4kids.com

Metalloids Have properties of both metals and nonmetals Located on either side of the zigzag line separating metals and nonmetals Most common is Silicon www.mvschools.org

Radioactivity Radioactivity: the process by which the nucleus of an atom releases energy and particles Marie Curie was the first person to isolate two radioactive elements (polonium and radium) An isotope is radioactive if the nucleus has too many or too few neutrons www.achievement.org

Radioactive atoms produce energy and particles from their nuclei The identity of these atoms changes because the # of protons changes. (radioactive decay) Occurs at a steady rate characteristic to each isotope The amount of time for one-half of the atoms to decay is called the half-life of the isotope Radioactive Decay earthsci.org

Radioactive Decay Parent decays into daughter isotope. Combination of both is 100% Parent starts at 100% and decays to 50% 100% 1 half-life to 50% (daughter 50%) 50% 2 half-lives to 25% (daughter 75%) 25% 3 half-lives to 12.5% (daughter 87.5%) 12.5% 4 half-lives to 6.25% (daughter 93.75%)