Early Atomic Theory and Structure

Chapter 5—Early Theories o What is stuff made of? o What makes something move? o How do we know it’s alive? o Is there a fundamental particle that everything is made up of? o Is there a universal constant to all matter?

Chapter 5.1 Early Thoughts o Roots of atomic theory are as old as 440 B.C. with Democritus’ idea of the atom o It took years for us to expand on this idea. The new theory was to be done by an English schoolmaster John Dalton in the early 1800s.

Dalton’s Atomic Theory o His theory included 6 postulates o 1. Elements are made up of atoms o 2. Atoms of the same element are alike o 3. Atoms of different elements are different by virtue of their size and mass o 4. Chemical compounds are formed by the union of two or more atoms of different elements o 5. Atoms combine to form compounds in whole number ratios (1:2 or 2:2, etc] o 6. Atoms of two elements may combine in different ratios to form more than one compound

5.2 Dalton’s Atomic Theory (cont.) o Why is it a Theory? o Which are still true? o Which do we know More info about now?

5.3 Composition of Compounds o The Law of Definite Composition states that a compound always contains two or more elements combined in definite proportion by mass

Law of Multiple Proportions o The Law of Multiple Proportions states that atoms of two or more elements may combine in different ratios to produce more than one compound

Subatomic Particles o Through the years of the late 1800s and into the early 1900s it was determined that there are three subatomic particles o Electrons (discovered first) o Protons (reasoned to exist if elements are neutral) o Neutrons (discovered last)

Electrons o 1. Electron which occupies the area outside the nucleus and has a negative charge, relative to the other subatomic particles it has negligible (so small that it can be ignored) mass.

Protons o 2. Proton which exists in the nucleus, has a positive charge and has mass roughly equal to neutrons

Neutron o 3. Neutrons (discovered last] functions as the glue that holds the nucleus together so that the protons don’t repel each other, it has no charge and roughly the same mass as the proton

Isotopes o Isotopes have same number of protons (so they are the same element) but different number of neutrons o Some isotopes are radioactive

Atomic Number o Atomic Number = the number of protons; unique to each element and the way the periodic table is arranged

Mass number o Mass Number = protons + neutrons (whole number o Cannot be found on the periodic table!

Check yourself o The nucleus is made up of what two types of subatomic particles?

Formulas you should know o Atomic number = # of protons o In an atom (uncharged): o # of protons = # of electrons o Mass # = # protons + # neutrons or o # neutrons = mass # - # protons o Charge = # protons - # electrons (for ions) o Remember the atomic # and # of protons give the element its identity and does not change

Elements composed of atoms Elements or atoms in an unbonded state have the same number of electrons as protons (They are neutral)

Ions Ions have an unequal number of electrons and protons. An atom loses or gains electrons to take on a charge (protons/neutrons are not transferred) Charge = #protons - # electrons

Ionic Charge o Charge is written in the upper RIGHT corner of the element’s symbol. o It is written with the number first and the sign second unless it is a + 1 or a -1 in which case it is just written as + or -. o Negative ions change their names to end in –ide like fluorine is fluoride

Ionic Notation X 3- This means that this element has a -3 charge.

Self Check o What is the charge of a substance with 14 protons, 15 neutrons, and 14 electrons?

Self Checker o If a substance has a charge of +2, this means that the number of protons is (circle one: LESS than or GREATER than) the number of electrons?

ISOTOPIC NOTATION isotopes are atoms with the same number of protons but different number of neutrons A Z X A = mass number (the total number of protons + neutrons) Z = atomic number (the total number of protons) X = element symbol

READING ISOTOPIC NOTATION Sc 46 = mass number (the total number of protons (21) + neutrons (25) 21 = atomic number 21 (the total number of protons (21)) Sc = element symbol In a neutral atom, the number of electrons (21) is equal to the number of protons.

PRACTICE PROBLEMS 15 N # protons = ____ # neutrons = ____ # electrons = ___ 35 P # p = ____ # n= ____ #e- = ___ 62 Cu 2+ # p = ____ # n= ____ #e- = ___ 76 Se 3- # p = ____ # n= ____ #e- = ___

Writing ISOTOPIC NOTATION 1.Write the symbol for the atom with an atomic number of 21 and a mass number of Give the complete chemical notation for the nuclide with 23 protons, 26 neutrons and 20 electrons. 3.Write the isotopic notation for a.Z = 46A = 110 b.An atom containing 24 protons, 28 neutrons, and 21 electrons c.Titanium Sc 49 V Pd 52 Cr Ti

PRACTICE PROBLEMS Pt 4+ # p = _____# n = _____ #e- = _____ mass number = ________ atomic number = _______ atomic mass = ________ name of element = _______ 2. Indicate the appropriate atomic mass of an element with 30 protons, 30 neutrons, and 28 electrons amu platinum amu

Atomic Mass o Atomic Mass = number on the periodic table reflecting the mass all isotopes known and their relative percentages (on periodic table below element’s symbol--usually not a whole number)

Atomic Mass oThe atomic mass of an element represents the average mass of all the isotopes found in nature. No element exists with only one possible isotope. Hydrogen has the smallest number of isotopes: 1 H protium, 2 H deuterium, 3 H tritium. Its atomic mass is amu (atomic mass units). The atomic mass is calculated by adding the % of 1 H mass found in nature to the % of 2 H mass found in nature plus the % of 3 H mass. o% 1 H + % 2 H + % 3 H = average mass (atomic mass) oGenerally the formula used is: % X + % Y + % Z… = atomic mass. An instrument called the mass spectrometer is generally used to determine the percentages and individual masses of each isotope.

Atomic Mass o Silver is found to have two stable isotopes, one has an atomic mass of amu and the other weighs amu. The first isotope represents % of the mass of the element and the second represents %. What is the atomic mass of the element silver? The equation to use is %X + % Y = average And remember to turn your percents into fractions before multiplying. (0.5182) amu + (0.4818) amu =? amu amu =? amu !! Now look at the periodic table to verify the answer.

PRACTICE PROBLEMS # 8 1. A sample of neon contains three isotopes, neon-20 (with an isotopic mass of amu), neon-21 ( amu) and neon-22 ( amu). The natural abundances of these isotopes are 90.92%, %, and 8.82 %. Calculate the atomic weight of neon. 2. There are only two naturally occuring isotopes of copper, 63 Cu and 65 Cu. Copper has an atomic mass of amu. What is the natural abundance of each isotope? 3. There are only two naturally occuring isotopes of gallium, 69Ga and 71Ga. What is the natural abundance of each isotope? amu 65 Cu = 30% & 63 Cu = 70% 69 Ga = 60% and 71 Ga = 40%

GROUP STUDY PROBLEM #8 _______1. The element with atomic number 53 contains a) 53 neutrons b) 53 protons C) 26 neutrons & 27 protons d) 26 protons & 27 neutrons _______2. The mass of one atom of an isotope is x g. One atomic mass unit has the mass of x g. The atomic mass of this isotope is a) amub) amuc) amud) amu 108 _______3. The number of neutrons in an atom of 47 Ag is a) 47b) 108c) 155d) _______4. The number of electrons in an ion of 13 Al 3+ is a) 13b) 10c) 27d) 14 _______5. What is the relative atomic mass of boron if two stable isotopes of boron have the following mass and abundance: amu (19.91%) & (80.09%) a) amub) amu c) amu d) amu

Test your Knowledge NameSymbolAtomic # # of protons # of neutrons Mass # # of electrons Neon11 Pb Carbon 8 F

Test your Knowledge NameSymbolAtomic # # of protons # of neutron s Mass # # of electro ns Neo n Ne LeadPb Tungste n W radiu m Ra Carb on C fluorin e F GoldAu

Table Information Hydrogen Symbol H Atomic Number1 Atomic Weight Oxidation States+1, -1 Electronegativity, Pauling2.2 State at RTGas, Non-metal Melting Point, K14.01 Boiling Point, K20.28

The Periodic Table o Horizontal rows are called periods o Vertical columns are called groups o We will use as group designations. o Group 1 is Alkali Metals o Group 2 is the Alkaline Earth Metals o Group 18 Inert or Noble Gases o Group 17 Halogens

Larger Groups o Groups 3 –12 are the heavy metals or transition elements o Two periods at the bottom are called the rare earth elements or the inner transition elements.