Download Atoms, Molecules, and Ions British chemist, John Dalton (1766 – 1844)

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Transcript
Atoms, Molecules, and Ions
British chemist, John Dalton (1766 – 1844) provided basic theory for modern
chemistry.
All matter, whether element, compound, or mixture is composed of small particles
called atoms.
Postulates of Dalton's Atomic Theory:
1. All matter is composed of indivisible atoms.
2. An element is a type of matte composed of only one kind of atom.
3. A compound is a type of matter composed of 2 or more elements combine in
definite arrangements.
4. A chemical reaction consists of the rearrangement of the atoms present in the
reacting substances to give new chemical combinations present in the substances
formed in the reaction.
Atomic symbols a one or two letter notation used to represent an atom
corresponding to a particular element.
Law of Multiple Proportions: If 2 elements A and B combine to form more than
one compound, then the masses of B that can combine with a given mass of A are
in a ratio of small whole numbers.
Example:
Structure of the Atom
Basic rule for the behavior of electrically charged particles – Like charges repel
each other; unlike charges attract.
Nucleus – +charged contains most of the mass of an atom.
Electron – - charged particle exists in the region around the nucleus.
British scientist JJ Thomson measured the cathode rays. He determined the chg to
mass ratio of 1.76 x108 C/g.
Robert Millikan succeeded in measuring the chg of an electron in the Millikan oil
drop experiment. Chg of an e’ = 1.602 x10-19 C.
Ernest Rutherford working w/ alpha particles bombarded golf & metal foil.
Atom – 3 subatomic particles, p, e, and neutron
Chg E’ = -1.602 x10E-19 C
Chg P = +1.602 x10-19 C
Chg N = 0
Nucleus consist of protons and neutrons
What makes an atom different in different elements?
Isotope - atoms of a given element that differ in the number of neutrons and
therefore in mass.
Atomic Mass Units (AMU) - a mass unit equal to exactly 1/12 the mass of a
carbon-12 atom.
Atomic Mass - average atomic mass for the naturally occurring element.
Isotope abundance Atomic weight for an element is the average weight of all of the isotopes for that
element. = weighted average.
Chlorine (Cl) - 2 major isotopes
35
Cl and 37Cl
Atomic wt = (% abundance isotope#1/100) (mass of #1) + (% abundance
isotope#2/100) (mass of #2)
% abundance = (# of atoms of a given isotope) / (total # atoms of all isotopes)
Example:
Period Table of the Elements
1869 Russian chemist, Demitri Mendeleev and German chemist Lothar Meyer,
working independently
Periodic Table- the arrangement of elements in order of increasing atomic # with
elements having similar properties placed in vertical rows.
Period - the elements in any horizontal row
Group - the elements in a vertical column also known as families.
Main Group elements (A group)
Metal
Nonmetals
Transition elements (B group)
Metalloids
Chemical Formulas
Notation that is used to convey relative proportions of atoms in the substance.
Molecule group of atoms that are chemically bonded together
Molecular formula gives the exact number of different atoms of an element in a
molecule.
Empirical formula is a chemical formula that gives only the relative number (ratio)
of atoms for each element in a molecule - simplest formula.
Ionic substances
Ion - an electrically charged particle obtained from an atom or chemically bonded
group of atoms by adding or removing electrons.
Cations vs. Anions
Ionic compound - composed of cations and anions.
Formula unit - the group of atom or ions explicitly symbolized in the formula
Naming compounds - chemical nomenclature
Naming Ionic compounds - first name the cation then follow with the anion
Common monatomic ions
Rules for Ionic compound
1. Monatomic cations are named after the element if there is only one such ion.
2. If there is more than one monatomic cation, the cation is named after the
element followed by a roman numeral.
3. The name of the monatomic anions are obtained from the stem name of the
element followed by the suffix -ide.
Polyatomic ion - an ion consisting of two or more atoms chemically bonded
together and carrying a net electric charge.
Binary compound - compound of only two elements
Rules for naming binary compounds
1. Name the first element using the exact element name
2. Name the second element by writing the stem name and adding suffix - ide
3. Add a prefix to each element name to denote the subscript of the element
(Table 2.6)
Oxoacid - an acid containing hydrogen, oxygen and another element.
Hydrates - a compound that contains water molecule weakly bound in its crystal
Chemical Equations - the symbolic representation of a chemical reaction in terms
of chemical formulas.
2Na + Cl2
2NaCl
Balancing Chemical Equations
Reactants - starting substances
Products - substances that result from a reaction
Strategy: Balance first the atom for elements that occur in only one substance on
each side of the equation.
Example:
CH4 + O2
H3PO3
CO2 + H2O
H3PO4 +PH3