Chapter 2: Matter is Made of Atoms

Chapter 2: Matter is Made of AtomsSection 2.1 Atoms and Their StructuresObjectivesRelate historical experiments to the development of the atom, Illustrate the modern model of an atom, Interpret the information available in an element block of the periodic table Hypotheses, Theories and LawsSolving a problem:1) Observation - use senses to observe the behavior of matter

2)HYPOTHESIS testable prediction Hypotheses that are verified by repeating experiments

Hypotheses, Theories and LawsEXPERIMENT: Investigation (with a control) designed to test a hypothesis

Hypotheses lead to scientific theoriesTHEORY: Explanation based on many observations and supported by the results of many experiments.Ex: Daltons Atomic TheoryHypotheses, Theories and LawsSCIENTIFIC LAW: Fact of nature that is observed so often that it becomes accepted as truth.A law can be used to make predictions, but does not explain why something happensExample: Sun rises in the east

Theories can explain laws

SCIENTIFIC METHOD: (p. 57, Figure 2.5)

Early Ideas about MatterGreek Philosophers (2500 years ago)4 Fundamental Elements- air, earth, fire, and waterQuestioned if matter could be divided endlessly into smaller pieces or if there was an ultimate small particle of matter Aluminum Foil

Democritus (dem-ock-rit-is) 460-370 B.C.

Proposed the world is made up of empty space and the smallest particles of matter are called ATOMS

This introduced the atomic theory of matter

Different types of atoms exist for every type of matter

Modern Atomic Theory Antoine Lavoisier (Luh-voh-zee-ay) 1782Concluded that when a reaction occurs, matter is neither created nor destroyedLaw of Conservation of MatterConservation of matter and recyclingAtoms are neither created nor destroyed

You cant throw anything away because there is no awayRecycling Nitrogen- Nitrogen is atmosphere is converted into compounds used on Earth, then returned to atmosphere (p. 53, Figure 2.4)

Recycling plastic, aluminum and glass- reusing atoms in these materials, we imitate nature and conserve natural resources (in natural processes atoms are recycled)

Joseph Proust 1799

Observed that the elements that composed compounds were always in a certain proportion by mass- LAW OF DEFINITE PROPORTIONS

Ex: water is always 11% H and 89% O by mass

Law of definite Proportions

Daltons Atomic Theory of Matter (1803)Theory essentially intact with small modifications to accommodate new discoveriesMain Points of Daltons Atomic Theory1. All matter is made up of atoms2. Atoms are indestructible and cannot be divided into smaller particles.3. All atoms of one element are exactly alike, but atoms are different for different elementsLate 19th century, experiments began to suggest that atoms are made up of even smaller particles (electrons, protons, neutrons)

Atomic StructureToday we know that atoms are made of smaller particles and Atoms of the same element can be nearly the same (but not exactly)

Cathode Ray Tube Experiment- J.J. Thomson (1897)Vacuum tube- positive and negative electrode- ray travels through tube from the to the +, rays bent toward + and away from the

Electrons, Protons, Neutrons

ELECTRON- negatively charged subatomic particleMass equal to 1/1837 the mass of a Hydrogen atom

PROTON- positively charged subatomic particleThe amount of charge on an electron and a proton is equal and oppositeThe mass of a proton is much greater than the mass of an electron (slightly less then a Hydrogen atom)

JJ Thomson Model

Atomic StructureUntil 1910, it seemed that atoms were made up of equal numbers of electrons and protons

J.J. Thomson discovered that Neon consisted of atoms of two different masses

Atomic StructureErnest Rutherford- 1909 Gold Foil Experiment (p.62, Fig 2.9)+ charged particles (alpha particles) sent through a gold foil most went straight through (empty space), few deflected (hit nucleus)Revealed the arrangement of the atom- 1911Atom is nearly all empty space with a small, dense, positively charged core called a NUCLEUS

http://micro.magnet.fsu.edu/electromag/java/rutherford/

Rutherford Model

Atomic StructureAtoms of an element that are chemically alike but different in mass are called ISOTOPESThe discovery of isotopes atoms must contain a third type of particle that explains mass differences

NEUTRON- neutral subatomic particleMass is equal to that of a proton but has no electrical charge

Existence of the neutron was confirmed in early 1930s

Bohr Model and Electron Cloud

Evolution of the atom (drawings)

Even smaller particles

Quarks small particles of matter that make up protons and neutrons.6 flavors or types top, bottom, charm, strange, up and downAn arrangement of 3 of these will form a proton, another arrangement will form a neutron.

NeutrinosSubatomic particles produced by the decay of radioactive elements Elementary particles that lack an electric chargeF. Reines would say, "...the most tiny quantity of reality ever imagined by a human beingNeutrinosCopiously produced in high-energy collisionsTraveling essentially at the speed of lightUnaffected by magnetic fields neutrinos Their unique advantage arises from a fundamental property: they are affected only by the weakest of nature's forces (but for gravity) and are therefore essentially unabsorbed as they travel cosmological distancesAtomic number and massesATOMIC NUMBER: Number of protons in the nucleus of an atom of that element

# of protons determines the identity of an element and many of its chemical and physical properties

Atomic number also tells us the number of electrons in a neutral atom of an element (p+ = e-)

Atomic Number and MassesMASS NUMBER: Sum of the protons and neutrons in the nucleus of an atom

Mass # = p+ + n0n0 = Mass # - p+Example: # of neutrons: mass # = 19 (Flourine) n0 = 19 - 9 = 10Atomic Number and MassesIsotopes have different mass numbers because they have different numbers of neutrons (they have the same atomic number)Isotopes are identified by placing the mass number after the name or symbol of the elementEx: Li-7, Li-6Ne-20, Ne-21, Ne-22

Periodic Table informationEach box contains: element, state, atomic number, symbol and average atomic mass (weighted average of the naturally occurring isotopes)Atomic mass example:Chlorine has 2 isotopes- Cl-37 and Cl-3524.2% is Cl-37 and 75.8% is Cl-35So the atomic mass is 35.45Protons, Neutrons, ElectronsParticle Symbol Charge Mass in grams Mass in uProton p+ 1+ 1.67 x 10-24 1.01Neutron no 0 1.67 x 10-24 1.01Electron e- 1- 9.11 x 10-28 0.00055u ATOMIC MASS UNIT (devised mass unit)1 u = 1/12 the mass of a carbon-12 atom1 u mass of single proton or neutron