2. Atoms and Periodic Table

3. Antoine Lavoisier Law of Conservation of Matter: matter can not be destroyed nor created.

4. Dalton’s Atomic Theory 1. All elements are composed of atoms. 2. Atoms of the same element are identical. Atoms of any one element are different than atoms of another element. 3. Atoms of different elements can physically mix together or can chemically combine in whole number ratios to form compounds.

5. 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element. Law of multiple proportions: different compounds made of the same elements, have mass ratios related by small whole numbers.

6. Ernest Rutherford Rutherford’s gold-foil experiment: the atom is mainly empty space with all the positive charge and almost all the mass centrally located in the nucleus.

7. Atoms Atoms are made of protons, neutrons, and electrons.

8. Atomic number The atomic number (often given as Z) of an element is the number of protons in the nucleus of an atom of that element. Since atoms are electrically neutral, the number of electrons (-) must equal the number of protons (+).

9. Atomic symbol Periodic Table

10. Isotopes Isotopes: same # protons, different # neutrons Symbol:

11. Atomic mass Atomic mass is a weighted average mass of the atoms in a naturally occurring sample of the element. Calculate: multiply the atomic mass of an isotope by its percentage/100. Do this for every isotope. Add the atomic masses found.

12. Isotopes Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?

13. Ga-69 68.9 amu x 60.2 = 41.5 amu for 69 Ga 100 100Ga-71 70.9 amu x 39.8 = 28.2 amu for 71 Ga 100 100 Atomic mass Ga = 69.7 amu

14. Abundance Percent abundance: % of total Relative abundance: Most abundant isotope set at 100 %, other relative to most abundant one.

15. Mass spectroscopy Mass spectroscopy is an analytical technique that helps identify the type and amounts of molecules and atoms (including isotopes) present in a sample. It measures the mass-to-charge ratio (m/z) of ionized samples.

16. Mass spectroscopy provides an accurate way of measuring the mass of atoms and molecules. Mass Spectroscopy

20. Periodic Table Horizontal rows: periods Vertical columns: groups or families Groups 1 and 2 (1A and 2A) and groups 13-18 (3A – 8A) are called representative elements Groups 3-12 are the transition metals Lanthanides and Actinides

21. Periodic Table Three main classes of elements: 1. metals 2. nonmetals 3. metalloids

22. Metals Most elements are metals. Properties: 1. Good conductors of heat and electricity 2. Solid at room temperature (except Mercury) 3. Reflect light (shiny) 4. Lose electrons in reactions

23. Non-metals Located in the upper right corner of PT Greater variation among these than metals. Most are gases at room temperature. A few are solids (C, S, P) and one is a liquid (Br) Tend to have properties opposite of metals. Gain electrons in reactions.

24. Metalloids Generally have properties similar to metals and nonmetals. An element in this group may behave like a metal under certain conditions, and then behave like a nonmetal under different conditions. For example, the metalloid Silicon is a poor conductor of electricity, but it becomes a good conductor when it is mixed with another metalloid, Boron.

25. Main groups Group IA  alkali metals Group IIA  alkaline earth metals Group VIIIA  noble gases Group VIIA  halogens – “salt formers” Group VIA  chalcogens Group VA  Nitrogen group Group IVA  IVA group Group IIIA  IIIA group