Atomic Theory

1
Atomic Theory

• Ancient Greeks believed that elements must be
  made up of small indivisible particles they
  called atomos, meaning indivisiblewhere the word
  atom comes from
• John Daulton, a school teacher, came up with the
  following hypothesis
• Atoms are the basic building blocks of matter
• They are the smallest particles of an element
  that retain its properties
• Atoms are extremely small about 10-10 m in
  diameteryou can fit a million atoms in a dot on
  your paper
• The central core, or nucleus, consists of two
  types of particles, protons neutrons, and is
  about 10,000 times smaller than the atom
• The majority of the atoms volume is where the
  electrons residecalled the electron cloud!

2
Atoms

• Protons have a positive electrical charge
• Neutrons, have no electrical chargethey are
  neutral
• Both Protons and Neutrons are located in the
  NUCLEUS, which is located at the center of the
  atomthe nucleus moves!
• Most of the mass of an atom is concentrated in
  the nucleusthe nucleus is held together by
  strong nuclear force
• In an atom with no charge, the number of
  positively charged protons is balanced by an
  equal number of small, negatively charged
  particles called electrons.
• Electrons have a high kinetic energy but little
  massthey are about 2,000 times smaller than a
  proton
• Remember, an atom that has an equal number of
  protons electrons will have no overall charge
• Electrons move around in a cloud outside the
  nucleus at different energy levels
• Each energy level holds a certain number of
  electronsThe first energy level can hold 2
  electronsThe second energy level can hold up to
  8 (atoms like to have a filled outer shell!!)
• Electrons do not orbit the nucleus in a defined
  path, it is impossible to know exactly where an
  electron is at any given time
• Electrons, which take up most volume of the atom,
  play a major role in chemical reactions

3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6
Atomic Number Atomic Mass

• All atoms of the same element will have the same
  amount of protonsthe amount of protons is the
  atomic number of that particular element
• The atomic mass of an atom is the number of
  protons PLUS the number of neutronsan electrons
  mass is so small it is not included in the mass
• Atomic Mass Atomic Number (Protons) Neutrons
• Atomic Mass Neutrons Atomic Number (protons)
• Atomic weight (average atomic mass) is the
  average of the atomic masses of the isotopes of
  each elementit is listed for each element of the
  periodic table

7
Elements

• Elements are pure substances that cannot be
  broken down chemically into simpler kinds of
  matter EACH HAVE THEIR OWN PROPERTIES
  (CHARACTERISTCS)
• They are made of only one type of atom each
  element is made of a different atom.
• There are over 100 known elements they are to
  molecules as the alphabet is to words All are
  located on The Periodic Table of the Elements
  which is in order of increasing atomic number
• Each element has a different chemical symbol that
  is composed of one or two letters
• Some of the words are abbreviations of their
  Latin names

8
Isotopes

• Atoms of the same element with different numbers
  of
• neutrons are called isotopes

9
Ions

• Electrons, which take up most volume of the atom,
  play a major role in chemical reactions and
  bonding
• Electrons move around in a cloud outside the
  nucleus at different energy levels, or distances
  from the nucleus
• Each energy level holds a certain number of
  electronsThe first energy level can hold 2
  electronsThe second energy level can hold up to
  8 (atoms like to have a filled outer shell!!)
• Electrons like to have a valence (outer) shell
  with 8 electrons!
• An Ion is an atom or a molecule where the total
  number of electrons does not equal the total
  number of protons, giving it an overall charge
• Ions form when an atom gains or loses one or more
  electrons, giving them an overall charge() ions
  are called cations, while (-) ions are called
  anions
• In general, metal atoms tend to lose electrons or
  form cations nonmetal atoms tend to gain
  electrons or form anions

10
Common Ions
11
Chemical Formulas and Chemical Reactions

• Chemical formulas show the proportion of each
  element in each compound (H2O) for example 2
  Hydrogen 1 oxygen atom
• Properties of a compound differ from the
  properties of the elements that compose
  itdepends on the type of bond
• Most elements undergo chemical reactions to
  become stablebonds break, form, and reform
• In nature, almost all elements do not exist by
  themselves as illustrated on the periodic table
• The same elements can make different
  compoundsthey have different chemical formulas
  (CO, CO2) (H2O, H2O2)look at the elements
  involved!
• In a chemical formula coefficients show how many
  molecules are present
• Subscripts show how many of each element are
  presentdont write 1
• In a chemical reaction, the molecules or elements
  to the left of the arrow are reactants, or what
  is present before the reactionto the right of
  the arrow are products, or what is formed from
  the reaction

NH3
Subscripts
12
Bonding

• In nature, most elements do not exist by
  themselves
• They are reactive, so they combine with other
  elements to form molecules and compounds
• A pure substance that is made up of atoms of two
  or more different elements is called a compound
• An elements ability to form compounds depends on
  the amount and arrangement of electrons in their
  outer energy levels
• An atoms outer energy level electrons are called
  valence electrons
• Atoms are stable when their outer energy level is
  filled!! They bond with each other to make them
  filled

13
BondIonic Bond Taken not shared

• Electrons move around in a cloud outside the
  nucleus at different energy levels
• Each energy level holds a certain number of
  electronsThe first energy level can hold 2
  electronsThe second energy level can hold up to
  8 (atoms like to have a filled outer shell!!)
• Sodium has one electron in its outer shell
• Chlorine has seven
• What needs to be done for each to become stable?
• Sodium becomes a positive ion, because it gives
  up an electron, while chlorine becomes a negative
  ion because it accepts an electronopposite
  charges attract, resulting in an ionic bondforms
  sodium chloride (table salt)
• Common between metals and non metals
• Ionic compounds are electrically neutral, so the
  charges will predict the ratio of atoms

14
COVALENT Bond

• Forms by the sharing of electrons between
  atomsbetween two nonmetals!!
• In the bond, no atom gains or loses electronsno
  ions are formed!
• Water, for example has one oxygen atom and two
  hydrogen atoms held together by covalent bonds
• If you recall, hydrogen needs two electrons to
  become stable in the outer energy level, and
  oxygen needs two (because it has six electrons in
  the outer shell)
• Therefore, in the presence of one another, they
  share electrons
• Compounds that dont share the electrons equally
  form POLAR COVALENT BONDS in which the electrons
  spend more time around one element, creating a
  polarized molecule

15
Metallic Bonds

• Metal atoms share electrons equally in all
  directions
• They are basically a nucleus in a sea of
  electrons
• This allows metals to be good conductors of
  electric current and heat
• This also gives them their high melting points
• What are some other characteristic properties of
  metals?