Chapter 3 Notes -In chemistry we must believe in things we cannot see -matter is made up of such tiny particles -everything is made up of matter -matter is composed of atoms atom- the smallest particle of an element that retains the properties of that element -atom in Greek means unable to cut -can fit 100,000,000 atoms in a 1 cm space

-atoms can only be viewed using special microscopes -Greek teacher Democritus first suggested the existence of atoms -John Dalton discovered the atom 2000 years later -said that atoms are indivisible

Dalton’s Atomic Theory all elements are composed of atoms all atoms of the same element are identical atoms of different elements combine to form compounds in simple whole number ratios atoms can be separated, rearranged, or joined to form chemical reactions

Structure of an atom nucleus- center of an atom -discovered by Ernest Rutherford in 1911 proton (p+) -positively charged subatomic particle -found in the nucleus of an atom -discovered by Eugen Goldstein in 1886 -mass= 1.67 X 10-24g

neutron (n0) -subatomic particle with no charge -found in the nucleus -discovered by James Chadwick in 1932 -mass= 1.67 X 10-24g electron (e-) -negatively charged subatomic particle -found surrounding the nucleus in energy levels or electron clouds -discovered by JJ Thomson in 1897 -mass= 9.11 X 10-28g

*atoms are electrically neutral because: # of p+ = # of e- -most of the mass is in the nucleus of that atom atomic number- number of protons in the nucleus of an atom (smaller number on the periodic table) -also = # of electrons b/c of above *

mass number- total number of protons and neutrons in an atom -larger number on periodic table -must be rounded to a whole number # of n0 = mass # - atomic # -element can be written as He-4

isotope- atoms of the same element having the same # of p+ and e-, but different # of n0. ex- Ne-20 10p+ 10e- 10n0 Ne-21 10p+ 10e- 11n0 Ne-22 10p+ 10e- 12n0

atomic mass- average mass of all the isotopes of an element -bigger number on periodic table unrounded -units are amu (atomic mass unit) relative abundance- which isotope is more abundant -is a % -the element that is most abundant is the one that has a mass closest to the atomic mass

ex- Cu-63 or Cu-65 Which is most abundant ex- Cu-63 or Cu-65 Which is most abundant? Cu-63 b/c its mass is closer to atomic mass

Modern Periodic Table -grew from the work of Dmitri Mendeleev -arranged elements according to increasing atomic mass Today -arranged in order of increasing atomic number -Henry Moseley did this in 1913 -called periodic law- when elements are arranged in order of increasing mass/atomic #, similar properties will recur

periods- horizontal rows groups/families- vertical columns, identified by a # and a letter Groups of the Periodic Table Alkali Metals- Group 1A elements Alkaline Earth Metals- Group 2A elements Transition Metals- Group B elements, bridge Inner Transition Metals- two rows at the bottom non-metals- upper and lower right side

Metalloids- staircase- starting at boron Halogens- Group 7A Noble Gases- Group 8A or Group 0 -also called inert gases- they do not react to form compounds Main group or Representative elements -Groups 1A to 7A minus the Transition and Inner Transition metals

Properties of Metals conduct electricity ductile (can be drawn into wires) shiny/lustrous malleable (can be pounded into sheets) -Most elements are solids Gases = H, O, N, F, Cℓ, He Ne, Ar, Kr, Xe, Rn Liquids = Hg, Br