3.2 Video Notes

• Model: A familiar idea used to explain unfamiliar acts observed in nature

• Theory: An explanation of observed facts & phenomena

  -explains all known facts

  -enables scientists to make correct predictions

• Democritus proposed the existence of an atom

  -word comes from the Greek word “atonnis” which means “not to cut” or “indivisible”

• Aristotle rejected the idea of the atom

  -said matter could be cut continually

• Dalton’s theory proposed that atoms:

  -are building blocks of matter & are indivisible

  -of the same element are identical & different for different elements

  -unite in small, whole-number ratios to form compounds

• J.J Thomson

  -credited with the discovery of electrons: a blow to Daltons indivisible atom

  -proposed the “plum pudding" model of the atom: negatively charged electrons embedded in a ball of positive charge

• Rutherfords Gold-foil Experiment:

  -aimed alpha particles at gold foil & most particles passed through

  -a few particles deflected & some particles bounced back

  -concluded that most of the atom is empty space & has a dense positively charged core

3.3 Atomic Structure Notes

• Rutherford referred to the area that is dense positively charged center is where all the mass is concentrated in an atom is known as the nucleus

  -composed of protons & neutrons (Chadwick helped Rutherford with the idea of a neutron)

  -Electrons are distributed around the nucleus (taking up most of the volume)

  -known as the nuclear model

  

• Protons have a positive charge & relative mass of 1.007276 amu

• Neutrons have no charge & a relative mass of 1.008665 amu

• Electrons have a negative charge & a relative mass of 0.0005846 amu

  -the space electrons move in accounts for most of the atomic volume

  -they’re the parts that “intermingle” when atoms combine to form molecules

• The number of electrons an atom has affects the way it can interact with other
  atoms

  - Atoms of different elements with different numbers of electrons = different chemical behaviors

• The atomic number of an element comes from the number of protons in the nucleus

• An atom’s mass number is found by taking the sum of the number of protons & neutrons in a nucleus

• Atoms are composed of identical protons, neutrons, & electrons

• Elements are different because they contain different numbers of protons

• # protons (in a neutral atom) = # electrons

• Atoms of a given element with a different number of neutrons & the same amount of protons are called isotopes

  -different masses

  

3.4 Introduction to the Periodic Table Notes

• The periodic table is an arrangement of elements in which elements are separated into groups based on a set of repeating properties

• Elements are listed on the periodic table in order of increasing atomic number

• The horizontal rows of the periodic table are called periods & the vertical columns are called groups or families

  -the elements in any group of the periodic table have similar physical & chemical properties

• Alkali Metals: silvery appearance, soft, very reactive, not found as free elements in
  nature

• Alkaline Earth Metals: harder, stronger, denser, & less reactive compared to alkali metals

• Transition Metals: good conductors of electricity, high luster, less reactive, & some free elements in nature

• Halogens: most reactive nonmetals, react w/ metals to form salts, & they exist as diatomic molecules

• Noble Gases: have filled energy levels & are not interested in reacting, don’t
  readily combine with other elements

  

• Most of the elements on the period table are metals

  -Efficient conductors of heat & electricity

  -Malleable (can be hammered into thin sheets)
  -Ductile (can be pulled into wires)
  -Lustrous appearance (shiny)
  -Mostly solids

• A relatively small group on the periodic table are nonmetals
  -Lack the properties that characterize metals, they’re poor conductors of heat & electricity
  - Show more variation in their properties than metals
  - Many are gaseous, only a few are solids, & Bromine is a liquid.

• Metalloids lie close to the “stair-step” on the periodic table

  - Often shows a mixture of metallic & nonmetallic properties
  - Sometimes called semimetals
  - Have characteristics of both metals & nonmetals (Semiconductors)
  🡪B, Si, Ge, As, Sb, Te, & Po.
  (Depending on the resource)

• Atomic Radius: the total distance from an atom's nucleus to the outermost

  orbital of an electron & increases to the LEFT & DOWN

• Ionization Energy & Electronegativity: the energy required to remove an electron from a neutral atom Increases UP & to the RIGHT

  

• Elements are not typically found in nature in their pure form.

• Diatomic molecule: A molecule composed of two atoms

• Diatomic element: An element that does not exist by itself & will combine with atoms of the SAME element to be stable

  -These elements are diatomic ONLY when they are alone, NOT when chemically
  bonded to another atom

  

• Only 2 elements are liquids in their elemental forms at 25 degrees Celsius

  -Bromine: heavy, reddish-brown liquid is the only non-metallic
  element that is liquid at room temperature

  -Mercury: heavy, silvery liquid, only metallic element that is liquid at room
  temperature

3.5 Ions/Valence Electrons Notes

• An atom that has gained or lost e- & thus acquired an electrical charge is called an
  ion

  -Ions can be anions or cations

• Octet Rule: An atom will gain, lose, or share electrons to have 8e- in its outer shell (valence shell)
  -Having 8 valence e- makes most atoms stable

  -Exceptions–H & He are stable with 2, other exceptions are in period 2

• Cation: positive ions from one or more electrons are lost from a neutral atom

  -named by their “parent atom” with a +

• Anions: negative ions from a neutral atom gaining one or more electrons

  -named by the root of their parent atom, adding the suffix ~ide, & a -

• Ions are NEVER formed by changing the number of protons in the atom’s nucleus

• Isolated atoms don’t form ions on their own, usually, ions form when metallic elements combine with nonmetallic elements

• Metal atoms tend to lose one or more electrons becoming cations which are, in turn, gained by the atoms of the nonmetal atoms forming anions

• The Group # (column #) is the # of valence e- that all atoms in that group have

• Valence electrons occupy the highest energy level of an atom

  -involved when atoms attach to one another

• Chemical bonds link atoms together, making them act as units

  -bond because they are more stable together than alone

• Electrons play a crucial role in forming bonds

  -Only the valence(outer shell) e- are involved, Inner core electrons
  e- do not form bonds
  • Bonds are formed when atoms transfer or share their valence electrons

• Ionic Compound: results when a metal reacts with a nonmetal to form cations
  & anions (requires a transfer of electrons, gaining or losing)

• The formula for ionic compounds = Both cations & anions must be present & net charge of the compound must be zero.

  -Electrically Neutral Overall

• Formulas for ionic compounds give the ratio of ions, not the total # of ions
  – In the ratio of cations:anions the charges will add & leave the compound with a 0 net charge