Chemistry Notes
Chapter 3 & 19.1 - Atoms, Ions, and Elements
Atomic Theories:
400 B.C. - Greek philosophers theorize on the existence of small subunits of
matter - particles that are "indivisible" called "atomos"
Early 1800's - Dalton's Atomic Theory
Late 1890's - Thomson's Cathode Ray Experiment
1920's - Rutherford's Gold Foil Experiment
1930's - Bohr's Quantum Mechanic Model
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Periodic Table of Elements: arranges elements in order of increasing atomic
number; attributed to Dmitri Mendeleev (1869)
Periodicity: elements with similar properties are arranged in groups that have
repeating patterns of characteristics and properties
7 Periods: Horizontal rows on the periodic table; corresponds to the energy level
(n) that the valence electrons reside on
8 Groups/Families: Vertical columns on the periodic table; correspond to the
orbital sublevel (l) that the electrons are located
Metals:
Group I - Alkali Metals (n) s1
Group II - Alkali Earth Metals (n) s2
Group III - Transition Metals (n) s2d1-10
Metalloids:
Group IV - Carbon Group (n) s2p2
Group V - Nitrogen Group (n) s2p3
Group VI - Oxygen Group (n) s2p4
Non-Metals:
Group VII - Halogens (n) s2p5
Group VIII - Noble Gases (n) s2p6
Metals: elements that are solids (except liquid mercury) with similar properties of:
1. good conductors of heat and electricity
2. have shiny luster
3. malleable - able to be hammered into sheets
4. ductile - able to be formed into thin wires
Mrs. Drurey
-1-
Newton South High School
Chemistry Notes
Chapter 3 & 19.1 - Atoms, Ions, and Elements
5. high tensile strength - able to resist breaking when pulled apart
6. very reactive, even with oxygen in the air
Ex. - Fe + O2 ----- Fe2O3
Iron (metal) + oxygen (gas) ---- iron III oxide (rusted metal)
Metalloids: "semi-metals" - elements that have properties of both metals and
non-metals
1. All solids at room temperature
2. less malleable than metals, but not as brittle as non-metals
3. good semi-conductors of electricity - used in computer chips, digital
screens, T.V., electronics
Non-metals: elements that are gases (except liquid bromine, solid carbon,
phosphorous, selenium, sulfur and iodine) and have similar properties of:
1. Poor conductors of heat and electricity
2. dull and have no luster
3. brittle and non-malleable
4. non-ductile
5. generally non-reactive (except Group VII - Halogens - these are the
most reactive non-metal group)
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Diatomic Molecules: natural elements that exist as 2 atoms
(H2, O2, N2, F2, Cl2, Br2, I2)
Atomic number: the number of protons in the nucleus of an atom
Mass number: the total number of protons and neutrons in the nucleus of atom
Cations: Positively charged ions
*When an atom loses an electron, it becomes more positively charged*
Mg
----- Mg2+ + 2eNeutral magnesium atom loses 2 electrons to become magnesium cation
Anions: Negatively charged ions
*When an atom gains an electron, it becomes more negatively charged*
Cl + e- -------- ClNeutral chlorine atom gains 1 electron to become chloride anion
Isotopes: Atoms with the same number of protons, but different numbers of
Neutrons
*Atoms cannot change the number of protons without changing their
identity*
Mrs. Drurey
-2-
Newton South High School
Chemistry Notes
Chapter 3 & 19.1 - Atoms, Ions, and Elements
Radioactive Decay - the spontaneous decomposition of a nucleus to form
another nucleus; atomic number and mass number are conserved
Alpha particle - helium nucleus produced in radioactive decay (heavy radioactive
nuclide)
Beta particle - radioactive nuclide decay that produces no change in mass
number, decreases atomic number by 1
Gamma particle - high-energy photon of light
Positron - same mass as electron, opposite in charge
Electron capture - inner-orbital electrons captured by the nucleus
Nuclear transformation - changes one atom into another by particle
bombardment
Geiger counter - detects radioactivity by using argon gas that becomes ionized
by rapidly moving, high-energy particles from radioactive decay
Scintillation counter - detects radioactivity when high-energy particle strikes
sodium iodide crystal and gives off light that can be measured
Half-life - time required for half of a sample to decay from its original amount
Radiocarbon or carbon-14 dating - objects that contain carbon can be dated by
measuring their carbon-14 : carbon-12 ratio
Fusion - combining 2 lighter nuclei of atoms to form a heavier nucleus
Fission - splitting of a heavy nucleus into 2 lighter nuclei
Mrs. Drurey
-3-
Newton South High School