ATOMS & THE PERIODIC TABLE OF ELEMENTS Chapter 3

CLASSIFYING MATTER What is matter made of? The ancient Greeks thought that everything in the universe was made up of a combination of 4 “elements”: air, fire, water, and earth. People believed this for many centuries! In the late 1600s, early chemists began to discover that this was not the case, that there are more than 4 elements and they are not what the Greeks thought they were. Now we know that all matter in the universe is made up of over 100 different kinds of elements.

ELEMENTS An element is a substance that cannot be broken down into any other substance by physical or chemical means (methods or ways). Like all matter, elements are identified by their physical and chemical properties.

THE ELEMENTS Name some elements ! Remember, these are substances that cannot be broken down into other substances. Elements are abbreviated by one or two letter symbols Examples: oxygen is O, calcium is Ca, carbon is C, aluminum is Al) Link

ATOMS What would happen if you tore a piece of aluminum foil into smaller and smaller pieces? What is the smallest possible piece of a substance? All matter is made up of atoms. An atom is the particle out of which all elements are made.

MOLECULES Atoms can combine and form a chemical bond, or a force of attraction between 2 or more atoms. A molecule is a group of 2 or more atoms held together by chemical bonds A molecule can be made of the same atoms or several different atoms Examples: O 2, H 2 0, CO 2, NH 3 How can oxygen (O 2) be both an element and a molecule? It is two or more atoms but they are the same element

COMPOUNDS A compound is a substance made of 2 or more elements that are chemically combined in a certain ratio. For example, carbon dioxide (CO 2 ) is 1atom of carbon and 2 atoms of oxygen. Carbon monoxide (CO) is 1 atom of carbon and 1 atom of oxygen. Compounds are made of molecules.

Table sugar has the chemical formula C 12 H 22 O 11. What is the ratio of carbon to oxygen in this compound? 12:11 Is H 2 O the same as H 2 O 2 ? Would you expect them to have the same properties? No, they are different substances (H 2 O 2 has one more oxygen) so they would have different properties.

BELLRINGER Without using a periodic table, what elements are represented by the symbols O, C, H, and Cl?

The properties of compounds are different that those of the elements they are made of. Example: sodium (Na) + chloride (Cl) = salt (NaCl)sodium (Na) + salt (NaCl) Why?? Because Na and Cl are different substances.

BELLRINGER Write an example of an element. Write an example of a mixture.

WHAT IS AN ATOM MADE OF? Positive center (nucleus) with a cloud of negatively charged particles around it

MOLECULE 2 or more atoms bonded together

11/6/14 1.Bellringer: How do you think people figured out that everything is made of atoms? 2.Video on development of atomic theory 3.Begin worksheets on atoms Announcements:  Science Fair Proposals due tomorrow ! (stay after school if you need help!)  All assignments and corrections also due tomorrow (end of MP 1)  Most recent quiz grades are up now but will not be on report cards

11/7 1.Bellringer: What are the 3 particles inside an atom? 2.Continue worksheets on atoms Announcements:  Science Fair Proposals due!  All assignments and corrections also due (end of MP 1)  Most recent quiz grades are up now but will not be on report cards

11/7 1.Bellringer: What are the 3 particles inside an atom? 2.Begin worksheets on atoms Announcements:  Science Fair Proposals due!  All assignments and corrections also due (end of MP 1)  Most recent quiz grades are up now but will not be on report cards

11/10 1.Bellringer: Write the 3 subatomic particles, their charges, and where they are located. 2.Begin notes on the Periodic Table 3.Science Fair proposals now late 4.Turn in atom packet if haven’t

11/17/14 1. Bellringer : What does an element’s atomic number tell you? 2.Sign up for your element project if you haven’t 3.Finish notes & videos 4.Worksheets & reading 5.Turn in proposals ASAP

SUBATOMIC PARTICLES Proton : positive ( + ), in nucleus Neutron : neutral ( 0 ), in nucleus Electron : negative ( - ), “orbits” nucleus in energy levels The proton of an atom of gold is the same as a proton of oxygen. Same for electrons and neutrons! All protons, neutrons, and electrons are the same. What makes elements different is the relative numbers of each.

ATOMIC NUMBER # of protons = atomic number Defines each element How the elements are arranged on the periodic table Number of protons equals number of electrons (unless it is an ion, or atom that is charged) Atoms of one element are different from atoms of another element because of their number of protons (atomic number)

Draw an atom of helium. Helium has 2 electrons, 2 protons, and 2 neutrons.

ISOTOPES Isotopes are atoms with a same number of protons but different number of neutrons Isotopes are identified by their mass number (sum of protons + neutrons) Electrons have very little mass

With a partner, on a blank sheet of paper, write the names of as many elements as you can think of (do not use a periodic table!) Now organize them into groups based on their characteristics. Every group must have more than one element in it.

THE PERIODIC TABLE Russian chemist Dmitri Mendeleev organized the elements into the Periodic Table in the 1870s Puzzle of the Periodic Table He did this by studying each element’s melting point, density, color, and atomic mass (average mass of all isotopes of that element) He predicted the existence of many elements that were discovered later!

11/18 Bellringer: Who arranged the elements into the Periodic Table?

THE PERIODIC TABLE Most periodic tables include the atomic number, chemical symbol, name, and atomic mass of each element Where did all the elements come from? All elements up to iron were created in stars, elements heavier than iron come from supernovassupernovas How did they get their names? Names of scientists, places, Latin/Greek, etc. Element Song

THE PERIODIC TABLE Although the Periodic Table is arranged by increasing atomic number, it is the arrangement of each element’s electrons that determines its properties There are 7 possible energy levels for electrons and 7 periods (rows) on the periodic table The periods go in order of increasing atomic # Elements in a group (column) have the same number of outermost ( valence ) electrons and react similarly Noble gases are unreactive because their valence orbitals are full Metals are on the left of the table, nonmetals on the right, and metalloids in between You can predict the properties of an element by knowing where it is on the Periodic Table!

11/24/14 Bellringer : How many electrons does this element have? How many neutrons does it have?

11/20/14 No Bellringer today We will begin with finishing the Element Song by going over The Gold Dust Kid, so finish it up first if you haven’t Then we will go over the What If reading Remainder of class, work on other worksheets or science fair proposals HW : Science Fair pkt pp. 6, 8, 10, 11, & 12 due Friday! Also, continue working on element project! (due Monday)

11/25/14 No Bellringer today All element presentations/posters due! Everyone with a Powerpoint needs to either share or it to me if you haven’t already! Over Break: All Science Fair proposals (initial sheet AND p. 6-12) should be done! If not, turn in ASAP!!! Begin working on your project. Tell me if you need help getting your materials. Do quiz corrections if you didn’t do well on it! Some people also never turned in Introduction to Atoms or Organizing the Elements worksheets!

Bellringer: What is the difference between a metal and a non-metal?

12/5 No bellringer Finish presentations! Begin notes on metals, etc. HW: finish Study Guide for Monday (some questions may not be able to answer yet—skip those and do the rest)

METALS Most elements on the Periodic Table Have physical properties like luster (shininess), malleability (can be hammered flat), ductility (can be made into wires), conductivity (good conductors of heat & electricity)

METALS Metals usually react by losing electrons When metals deteriorate due to chemical reactions with substances in the environment (like oxygen or water) it is called corrosion. Example of corrosion: rust

METALS Alkali metals (group 1) are the most reactive metals Are never found uncombined (alone) in nature Alkaline earth metals (group 2) are harder, denser, and melt at higher temps, and are less reactive than the alkali metals Transition metals (group 3-12) are hard, shiny, with high melting pts and densities, less reactive

NON-METALS Lack the properties of metals Poor conductors, dull, brittle Many are gases at room temp; some are solids (C, S, I), bromine is the only liquid On the right side of Periodic Table (except Hydrogen) Usually gain or share electrons when they react

NON-METALS Halogens (group 17), like chlorine, are the most reactive nonmetals Noble gases (group 18), like neon, are usually nonreactive

METALLOIDS Metalloids have some properties of metals and some properties of nonmetals Examples are silicon & arsenic

RADIOACTIVE DECAY Remember what an isotope is.. An atom that has a different # of neutrons than usual Some isotopes are unstable, meaning they undergo radioactive decay

12/9 Please get out your notes from yesterday and your (completed!) study guide NO TUTORING OR AFTER SCHOOL TODAY! No bellringer

RADIOACTIVE DECAY Radioactive decay is when a nucleus gives off alpha or beta particles and/or energy in the form of gamma rays This is a nuclear reaction This changes the identity of the atom (because if protons are lost, the atomic # changes); it becomes a new element Something is radioactive if it does radioactive decay

RADIOACTIVE DECAY Radioactive dating is using isotopes to determine how old something is This is done by knowing the half life of the isotopes, or how long it takes for half of it to decay Isotopes are also used as tracers (see where things go)