introduction to atoms. what are atoms? an atom is the smallest particle into which an element can be...
Post on 19-Jan-2018
229 Views
Preview:
DESCRIPTION
TRANSCRIPT
Introduction to Atoms
What are atoms?
An atom is the smallest particle into which an element can be divided and still be the same substance.
History of the Atom
History• Democritus – first person to use the word atom, comes from
the Greek word atoma, means “indivisible”• John Dalton came up with the atomic theory• JJ Thomson did experiments using a cathode ray tube, came
up with model that included positive and negative charges• Ernest Rutherford did the Gold Foil experiment, which
changed the model to a positive nucleus surrounded by electrons
• Niels Bohr determined that electrons move in specific distances from the nucleus based on how much energy they have
Atomic theory
The atomic theory states 5 things:1.All matter is made up of atoms
2.Atoms are neither created nor destroyed in chemical reactions (Law of conservation of mass)
3.Atoms of different elements combine in whole-number ratios
4.Each element is made of a different kind of atom
5.The atoms of different elements have different mass and properties
Parts of an atom
Protons – positively charged particles found in all atoms
Neutrons – particles found in all atoms that do NOT have a charge (neutral charge)
Electrons – negatively charged particles found in all atoms
Nucleus
Center of the atom that is extremely dense, positively charged region that contains BOTH protons and neutrons
Protons and neutrons = mass number
Electron cloudsRegions inside the atom, located outside surrounding the nucleus with negatively charged particles (electrons)
Bohr proposed that electrons move in paths at certain distances around the nucleus = BOHR MODEL
Next time – Atoms and the periodic table
Copy the entire figure, drawing and words from page 312, Figure 11
Atomic mass unit (amu)
The SI unit used to express the masses of the particles of an element
Each proton has a mass of 1 amuEach neutron has a mass of 1 amuElectrons are so small that they have a mass unit
of almost zero
Atomic number
How can you tell which elements these atoms represent?
Atomic number – number of protons in the nucleus of an atom
Isotopes
Are all atoms of an element the same? NOIsotopes – atoms that have the same number of
protons but different number of neutronsEach element has a limited number of isotopes
that occur naturally
Mass number
Protons + neutrons = mass numberUsed to determine if an element is an isotope
Atomic mass
Weighted average of masses of all the naturally occurring isotopes of an element
MATH BREAK – pg 316 , do in your science journal
Physical Property Color, odor, mass, volume
Physical Properties Definition ExampleThermal conductivity The ability to transfer
thermal energy from one area to another
Plastic foam is a poor conductor, so hot chocolate in a plastic foam cup will not burn your hand.
State The physical form in which a substance exists , such as a solid, liquid, or gas
Ice is water in its solid state.
Malleability The ability to be pounded into thin sheets
Aluminum can be rolled or pounded into sheets to make foil.
Ductility The ability to be drawn or pulled in a wire
Copper is often used to make wiring.
Solubility The ability to dissolve in another substance
Sugar dissolves in water.
Density Mass per unit volume Lead is used to make sinkers for fishing line because lead is more dense than water.
Physical vs. Chemical PropertiesSubstance Physical property Chemical property
Helium Less dense than air nonflammable
Wood Grainy texture flammable
Baking soda White powder Reacts with vinegar to produce bubbles
Powdered sugar White powder Does not react with vinegar
Rubbinmg alcohol Clear liquid flammable
Red food coloring Red color Reacts with bleach and loses color
Iron malleable Reacts with oxygen
Tin malleable Reacts with oxygen
top related