Unit 2: Atomic Theory Flashcards
Democritus’ Theory
Democritus believed all matter was made of fire, air, water, and earth. Democritus thought the ratio of these four elements affected the different properties of matter.
Atomos
Means indivisible. Democritus called immeasurable small pieces of matter atomos, and he thought they were eternal and couldn’t be destroyed.
John Dalton’s 1st Postulate
All elements are composed of tiny indivisible particles called atoms.
John Dalton’s 2nd Postulate
Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
John Dalton’s 3rd Postulate
Atoms of different elements can physically mix together or chemically combine in simple whole-number ratios to form compounds.
John Dalton’s 4th Postulate
Chemical reactions occur when atoms are separated, joined together or rearranged. Atoms of one element are NEVER changed into another element during a chemical reaction.
J.J. Thomson’s Atom Model
Called the “Plum Pudding Model” because the positively charged sphere is the pudding and the electrons are the plums spread out through the pudding
J.J. Thomson Contribution
Discovered the electron with the cathode ray experiment and he discovered that electrons are negatively charged
Ernest Rutherford’s Contribution/Model
Gold Foil Experiment:
1. The atom contained a nucleus that consisted of protons and neutrons and was very dense
2. The electrons of an atom were located outside and surrounded the nucleus
3. Most of the atom is empty space
4. Discovered the proton and its charge
James Chadwick’s Contribution
Discovered the neutron
Dmitri Mendeleev organized elements according to…
atomic mass
Henry Moseley organized elements according to…
atomic number
Periodic Law
The appearance of similar properties for elements when arranged in order of increasing atomic number
Valence Electrons
Electrons found in the outer shell of an atom. Important because they are the electrons that react with other atoms. Also, they determine the chemical properties of an atom.
Group 1 of the Periodic Table
Alkali Metal
Group 2 of the Periodic Table
Alkaline Earth Metals
Group 3-12 of the Periodic Table
Transition Metals
Group 17 of the Periodic Table
Halogens
Group 18 of the Periodic Table
Noble Gasses
Metals
80% of all known elements
Left and center of the periodic table
Lustrus (shiny)
Malleable (hammer into thin sheets)
Dutile (make into thin wire)
Good conductors of heat and electricity
Metalloids
Touch the staircase and have properties of both metals and nonmetals. (Note: Al is a metal!)
They are semiconductors which means they normally do not conduct electricity but will conduct at high temperatures or when certain subjects are added.
Nonmetals
Most are located in upper right of periodic table
Most are gaseous at room temperature
Right of the periodic table and hydrogen
Non-lustrous (dull)
Brittle (breaks easily)
Poor conductors (good insulators)
The 7 Metalloids
Boron
Silicon
Germanium
Arsenic
Antimony
Tellurium
Astatine
Alpha Particles
2 protons and 2 neutrons/He
heavy
positive
3-5 cm
paper; skin
DNA mutation and/or cell death
Can detect smoke
Beta Particles
electron
light
negative
2-3 m
glass; metal; water
Can cause cancer and/or cell death
Can be used in cancer treatment
Gamma Rays
wave/00y
no mass
neutral
very far (galaxies)
water (large amount); concrete; lead
Can sterilize food
Fission
The splitting a heavy nucleus into two nuclei with smaller mass numbers.
Fusion
The combining two light nuclei to form a heavier, more stable nucleus.
Half-life
The time it takes for one-half of a radioactive isotope to decay.
Radioactive Isotopes with Short Half-lifes
Are especially dangerous because they can emit a lot of high energy particles (alpha and beta) and/or electromagnetic radiation (gamma rays) in a short period of time
Positron
positive electron
Stable Nucleus =
neutrons/atomic # = 1
Closer to 1 = more stable nucleus
Alkali Metals
Alkali metals are NEVER found pure in nature; they are too reactive
Reactivity of these elements increases down the group
Alkaline Earth Metals
Alkaline earth metals are less reactive than alkali metals
Alkaline earth metals are not found pure in nature; they are too reactive
The word “alkaline” means “basic”
Halogens
Halogens are never found pure in nature; they are too reactive
Halogens in their pure form are diatomic molecules (F2, Cl2, Br2, and I2)
Noble Gasses
Noble gases are ONLY found pure in nature – they are chemically unreactive
Colorless, odorless and unreactive; they were among the last of the natural elements to be discovered
