Chapter 3 Discovering the Atom
Essential Questions • How was the idea of the atom developed historically? • What important experiments were performed to change our view of atoms? • What are Subatomic Particles? • What is the Modern View of the atom? • What is Atomic Mass?
Changes in The Way We View Matter • The ___________view of __________was based on __________and not on ______________data. • In 1661, _____________published a proposal that a substance was not an ___________if it was made of two or more _________________.
Changes in The Way We View Matter • 1760’s - _____________defines the compound.
Experiments That Changed The Way We View Matter • The Law of ____________of __________.(1774)
Dalton’s Atomic Theory • Elements are made of _______particles called __________. • All _________of a given element are ___________. • The _________of a given element are ___________from those of any other __________.
Dalton’s Atomic Theory • Atoms of _____element can combine with atoms of _______elements to form _____________. A given __________always has the _______relative _________and ________of atoms.
Dalton’s Atomic Theory • Atoms are ____________in _______processes. That is, atoms are not _________or __________in chemical reactions. A chemical reaction simply __________the way the atoms are ___________together.
Law of Constant Composition • IFA given __________always has the _______relative ______and _____of atoms, • THEN a given _________always ______the _______proportion (by _____) of the elements.
An Example • Water always contains ____times as much oxygen (by mass) as hydrogen. • 9 grams of water contains ____grams of oxygen and ___gram of hydrogen. • 27 g of water has _____g of oxygen and ___g of hydrogen. • What about 100 g of water?
From the other direction • 8.00 g of oxygen will react with 1.00 g of hydrogen to form ______g of water. • If you mix 24 g of oxygen with 6 g of hydrogen and react them, how much water can you form?
Lab on Constant Composition • Potassium chlorate contains 31.9% potassium, 29.0 % chlorine, and 39.2% oxygen (by mass). • This should be _____for all samples of _____potassium chlorate.
Lab on Constant Composition • If you heat potassium ________you get potassium _______and _______: 2 KC1O3 → 2 KCl+ 3 O2 • We will carry out this _____________and measure how much _______we gave off (by difference).
Review of Chemical Formulas • Each atom present is represented by its _________symbol. • The _________of each type of atom is indicated by a ____________written to the right of the element symbol. • When only _______atom of an element is present, the subscript ____is not written.
Some Formulas • KClO3 • H2O • CH4 • C12H22O11 • S8
The Structure of the Atom • Until the work of ______________, scientists believed that atoms were the _________possible ___________. • Cathode ray tube – led to the ___________of the ___________by _____________.
MODERN ATOMIC STRUCTURE The _____________charge is found in the nucleus. Therefore, _____________are located in the nucleus. The number of __________held by the nucleus is called ATOMIC _______. _____________move about the ____________and account for most of the _____________of the atom.
DISCOVERING NEW FORMS OF HYDROGEN In the early 1930’s, a new form of hydrogen was discovered. It accounted for 0.015% of all hydrogen in nature. The only difference was that it was twice as heavy as the most common form of hydrogen(99.985%). It was, therefore, called heavy hydrogen. Atomic # Atomic Mass# of p# of e H Heavy H Why is heavy hydrogen twice as heavy?
A NEW SUB-ATOMIC PARTICLE In 1935, an English scientist of the name ___________discovered a new particle. Its characteristics were: a. Its mass was basically the _________as that of the ______. b. Its charge was ____________. ______________, therefore, called this a _____________.
ISOTOPES Apparently, ___________hydrogen contains a ___________making it twice as ______________. Mass Number = the sum of the number of ___________and ____________or sum of _____________. Isotopes – atoms of the _________element that have the _______number of ___________, but a different number of ___________. – have the same atomic __________, but different ________ number Neutrons = ________Number – Atomic ___________
ISOTOPES CONTINUED At.#Mass ##p#e#n 32He 42He 168O 178O 188O
ATOMIC MASS This is the relative mass of an ________based, temporarily, on _____________as exactly 1. Hydrogen Chloride – 2.74% H and 97.3%Cl Water – 11.1%H and 88.9%O Ammonia – 17.6%H and 82.4%N Salt – 39.3%Na and 60.7%Cl
ATOMIC MASSES Old system: H-1 = 1.0000….. C-12 = 11.9987 New system: C-12 = 12.00000…… H-1 = 1.007825 So atomic mass is defined as the __________mass of an atom based on __-12 as exactly _____.
AVERAGE ATOMIC MASS %PRESENTATOMIC MASS H-1 99.985% 1.007825 H-2 0.015% 2.01410 Ave. Atomic Mass = 1.00797 TEXT BOOK ATOMIC MASS This is the the average of the atomic masses of the isotopes of an element based on C-12 as exactly 12
CALCULATING ATOMIC MASSES % PRESENTATOMIC MASS Cl-35 75.77% 34.969 Cl-37 24.23% 36.966 Ave. Atomic Mass = ? C-12. 98.892% 12.0000… C-13 1.108% 13.00335 Ave. Atomic Mass = ?
Subatomic Particles • _______________-- are subatomic particles that comprise known matter and anti-matter. • ______________--Do not help hold an atom’s nucleus together and are found in known matter. • Are neutrinos and electrons • _______________ • Particles such as the proton or neutron.
Quarks • Quarks--Does not help hold an atom’s nucleus together. • Quarks are extremely ___________, • classified by the _________and _________of charge that they hold, • are the most ______________particles discovered to date.
Bosons and Leptons and QUARKS – Oh MY! TYPES OF QUARKS • Up +2/3 • Down -1/3 • Top (aka Truth) • Bottom (aka Beauty) • Charm (aka Charmed) • Strange (aka Strangeness) Proton – 2 Ups and 1 down, 2(2/3) + (-1/3) Neutron – 1 Up and 2 Downs, (2/3) + 2(-1/3)
Atomic Masses and the Law Of Constant Composition • Remember that the Law of Constant Composition states “a given compound always contains the same proportion (by mass) of the elements.” • This now makes perfect sense with what we know about relative masses.
Water • Oxygen has an relative mass of ______ compared to hydrogen’s _____. • ______grams of oxygen has as many O atoms as ______ grams of hydrogen has H atoms. • ____ grams of hydrogen has twice as many H atoms as _______ grams of oxygen has O atoms. • The mass ratio in water (H2O) is ___:__ or ___:___
Mass Ratios • Carbon and hydrogen react in a ___:____ mass ratio to form methane (CH4). • How many grams of carbon would react with 6.0 grams of hydrogen? • 18 g • How does this relate to Atomic Masses?
AlH3 • What is the mass ratio for AlH3? • Al = __________, H = _____Therefore mass ratio = __________/__ or ___:___ • How many grams of hydrogen would react with 18 grams of aluminum? • 2 g • How many grams of AlH3 would form from the reaction of 18 grams of aluminum and 6 grams of hydrogen? • 20 g
PERIODIC TABLE The elements are arranged in the Periodic Table in order of increasing ______ __________. When elements are arranged this way, the chemical and physical properties re-occur in a __________fashion. (Dimitri Mendeleev) Horizontal Rows – ___________ Vertical Columns – ___________
Periodic Law • When the elements are arranged in order of increasing __________ ___________ there is a periodic repetition of their chemical and physical properties. • The chemical and physical properties of the elements are a _________function of the _________ _____________.