Ch4 and Ch5 Atomic History and the Atom
Ch4.2 What are atoms? Atoms are the smallest part of an element that still has the element s properties.
Ch. 4.3 The Atom is Defined 400 B.C. the Greek philosopher Democritus said that the world was made of two things: Empty space and tiny particles called atoms
Early 1800 s John Dalton Came up with first atomic theory that is the basis for today s theory.
Early 1800 s John Dalton s Theory-proven 1. Every element is made of tiny, unique particles called atoms These atoms cannot be destroyed, but instead rearrange during a chemical change 2. Atoms of different elements can join to form molecules in constant whole number ratios. Law of Multiple Proportions
John Dalton s Theory-proven Law of Multiple Proportions
John Dalton s Theory-disproved Atoms cannot be broken down into smaller particles. Atoms of the same element are exactly alike in mass Why?
Law of conservation of matter Matter cannot be created or destroyed. It only changes its state or rearranges its atomic structure.
Law of Conservation of Mass
Conservation of Mass
1897 JJ Thomson Used a cathoray tube to examine if atoms were made of charged particles.
Opposite charges attract
1897 JJ Thomson Discovered atoms are made up of particles with negative charges. Called them electrons.
Thomson Model Electrons Positive charges, not known as protons yet
1913-Rutherford Put together a team of physicists to performed the gold foil experiment
1 out of 8000 alpha particles were repelled.
1913-Rutherford The experiment led to the discovery that atoms are mostly empty space. It also discovered that atoms contain a positive nucleus which contained most of the mass of the atom.
Rutherford Model
Nucleus positively charged (protons) makes up 99.9% of the atom s mass Also contains neutrons (James Chadwick)
Parts of an atom Nucleus Proton Neutron Cloud Subatomic Particles Charged Particles Electron
Protons Charge (+) Mass is equal to 1 atomic mass unit (amu) Identifies atom
Neutrons Net Charge (0) - neutral Mass is equal to 1amu Determine stability of nucleus
Electrons Charge is negative (-) Mass is equal to 0.001 amu
The Periodic Table Atomic Mass
Ch. 4.4 Atomic Number Identifies # of protons
Atoms Charge All atoms have the same number of protons and electrons. They are neutral. Charges cancel each other out.
Mass Number Mass of a single atom # of protons # of neutrons Mass #
Ch 4.5 Isotopes Any atoms having the same number of protons but different number of neutrons. So they also have different mass numbers.
Springfield Isotopes
Isotopes
Average Atomic Mass Atomic mass is the mass of all isotopes of a particular element averaged together Calculated by using the mass of each isotope and the % abundance.
Ions Ions are charged particles. Form when atoms lose or gain electrons. Form in order to have a full outer shell Two Types.
Cations Positively charged ions. Form when atoms lose electrons. Form from metal atoms
Cations # of protons greater than # of electrons More (+) than (-)
Na Atom Na + Cation
Anions Negatively charged ions. Form when atoms gain electrons. Form from nonmetal atoms
Anions # of protons less than # of electrons More (-) than (+)
Cl atom Cl - Anion
Electromagnetic Spectrum Electromagnetic spectrum includes light at all possible energies, frequencies, and wavelengths frequency, energy Wavelength
Ch5.1 Modern View of Atom The study of light led to a new way of examining the atom. No longer just a particle view
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Gamma Rays highest energy and frequency. Nuclear radiation
X-Rays high ionizing energy radiation Used for imaging
Ultraviolet Light (UV) Ionizing energetic radiation Can cause skin cancer when over exposed
Sun Protection (SPF) 7 or less no protection 8 Extra protection but still permits tanning 15 Offers total protection from burning 30 Totally blocks UV
ROYGBIV Visible spectrum We see red and orange the best Blue and violet are the hottest colors, and emits the most energy, red the least and coldest White is all the colors combined, black the absence
Infrared Light Lower energy radiation Night vision
Microwaves Low energy radiation Used to heat food Also used in telecommunication
Radio Waves Have the Lowest frequencies and highest wavelengths Includes FM, AM, and TVs Radar
REALITY TV
(Ch 5.2) 1920s Niels Bohr Suggested that electrons move around atoms in set paths around the nucleus. (solar system)
1920s Niels Bohr He said each path is an energy level Atom s electrons can jump to different energy levels when absorbing photons (particles of light)
Niels Bohr States of Atoms Ground State- An electron s lowest energy state or level Excited State- An electron that is energized will jump to a higher energy state or level. Will last for a short period. (resulting light production)
States of Atoms? Ground State Excited state
This is how light is produced Ground State Excited state back to ground And Light production
Ch 5.2 Niels Bohr Bohr noticed that different atoms emitted different radiation when excited.
Flame Test
Atomic Spectra All elements emit photons carrying different amounts of energies that can be directly related to their frequencies. chemistry of SPEC-TROS-COPY Each line on spectrum is an emitted photon
Spectroscopy
Emission (Line) Spectrum Atoms and molecules are identified by these spectrums.
What the heck is light?
Ch5.3 Today s Theory It is impossible to determine an electron s exact position and speed at the same time. (Hiesenberg) Disproving Bohr s definite path/orbit assumption
Ch5.3 Today s Theory Wave-Particle Duality of atoms Electrons move around in such a way that they exhibit both wave and particle properties. Light does the same thing (photons).
Ch5.3 Today s Theory Electron positions are based on probability. (orbitals) This led to the Electron Cloud model
Modern Atomic Cloud Model
History Review
Ch. 5.3,4,5 Energy levels Electrons are found throughout different energy levels. Within these energy levels are orbitals. Each of these levels can only hold a certain amount of electrons
Energy levels 1 st level holds 2 e - 2 nd level holds 8 e - 3 rd level holds 8 e - or 18e- 4 th and greater level holds 8, 18, or 32 e- Outer (valence) level holds up to 8 e-
Valence Electron The number of electrons in the outermost electron shell. Most important
Making Bohr Models
Bohr s Model Blue dots represent electrons Rings represent energy Level, NOT orbit (path)