Atoms, Molecules, & Ions
Chemical Symbols
• Z = protons
• A – Z = neutrons
– Isotopes will have the same
atomic numbers but different
mass numbers, therefore a
different number of neutrons.
• Charge
– Generally indicated in the top
right hand corner
– A positive charge indicates
the loss of electrons
– A negative charge indicates
the gaining of electrons
A Covalent Bond
Naming Covalent Compounds
– Name the first element an change the ending
of the second to –ide.
– Must use prefixes to indicate the # of atoms of
an element in the molecule.
– Never use mono- when there
is only one of the 1st element.
Naming Covalent Compounds
Practice
Give the correct name:
• PCl5
• CS2
• N2O4
• XeF4
• SO3
* Know the common name:
H2O
NH3
N2H4
Give the correct
formula:
• Silicon dioxide
• Dinitrogen monoxide
• Selenium
hexaflouride
• Hydrogen fluoride
• ammonia
An Ionic Bond
Naming Ionic Compounds
• Alkali, alkaline, & silver, zinc, aluminum metals
bonded to non-metals:
– Name the metal (no roman numerals are necessary)
and change the ending of the second element to –ide
(names of polyatomic ions do not change).
• Transition & Post-Transition metals to nonmetals:
– Name the metal, need to include a roman numeral
representing the charge of that metal and the ending
of the second element changes to –ide.
– Using a t-chart helps determine the charge on the
metal.
Common Transition Metal Ions
Ionic Bond Strength
Ionic Naming Practice
Give the correct name:
• Fe(ClO4)2
• SnCl4
• Cr2(SO4)3
• PbO
• CuCl2
Give the correct
formula:
• Manganese II nitrate
• Ammonium sulfite
• Copper I chromate
• Lead II iodide
• Mercury II oxide
Naming Acids
• Binary Acids
• Oxy-acids
– The prefix hydro- is never used. Always begin with the
polyatomic ion name and change the ending as
follows:
• -ate in the anion becomes -ic in the acid
• -ite in the anion becomes -ous in the acid
Naming Acids Practice
Give the correct name:
• H3N
• HCN
• HI
• HC7H5O2
• H2CO3
Give the correct
formula:
• Nitrous acid
• Hypochlorous acid
• Hydrochloric acid
• Sulfuric acid
• Phosphorous acid
Hydrates
• Ionic compounds called hydrates have a
specific number of water molecules associated
with each formula unit.
• In their formulas, this number is shown after a
centered dot.
– Epsom salt has the formula MgSO4·7H2O and the
name magnesium sulfate heptahydrate.
– The mineral gypsum has the formula CaSO4·2H2O
and the name calcium sulfate dihydrate.
• Heating can remove some or all of them, leading
to a different substance.
– For example, when heated strongly, blue copper(II)
sulfate pentahydrate (CuSO4·5H2O) is converted to
white copper(II) sulfate (CuSO4).
Naming Hydrates Practice
• Cupric nitrate trihydrate
• Barium hydroxide octahydrate
PROBLEM Something is wrong with the second part of
each statement. Provide the correct name or formula.
(a)
(b)
(c)
(d)
Ba(C2H3O2)2 is called barium diacetate.
Sodium sulfide has the formula (Na)2SO3.
Iron(II) sulfate has the formula Fe2(SO4)3.
Cesium carbonate has the formula Cs2(CO3).
Covalent vs Ionic
J.J. Thompson
Robert Millikan
Ernest Rutherford
Mass Conservation
• The most fundamental chemical observation of the 18th
century was the law of mass conservation:
– the total mass of substances does not change during a chemical
reaction. The number of substances may change and, by
definition, their properties must, but the total amount of matter
remains constant.
• Even in a complex biochemical change, such as the
metabolism of the sugar glucose, which involves many
reactions, mass is conserved:
Constant Composition
• Another fundamental chemical observation is
summarized as the law of definite (or constant)
composition:
– no matter what its source, a particular compound is
composed of the same elements in the same parts
(fractions) by mass.
• The fraction by mass (mass fraction) is that part
of the compound’s mass that each element
contributes. It is obtained by dividing the mass of
each element by the total mass of compound.
• The percent by mass (mass percent, mass %) is
the fraction by mass expressed as a percentage.
Law of Constant Composition
Law of Multiple Proportions
• Dalton’s law of multiple proportions:
– if elements A and B react to form two compounds, the
different masses of B that combine with a fixed mass of A
can be expressed as a ratio of small whole numbers.
• Consider two compounds that form from carbon
and oxygen; for now, let’s call them carbon oxides I
and II. They have very different properties. For
example, measured at the same temperature and
pressure, the density of carbon oxide I is 1.25 g/L,
whereas that of II is 1.98 g/L. Moreover, I is
poisonous and flammable, but II is not. Analysis
shows that their compositions by mass are:
MC 1
• Which of the following represents a pair of
isotopes?
Atomic # (Z)
Mass # (A)
A
I.
II.
6
7
14
14
B
I.
II.
6
14
7
14
C
I.
II.
6
14
14
28
D
I.
II.
7
7
13
14
E
I.
II.
8
16
16
20
MC #2
Which of the following characteristics is common
to elemental sulfur, chlorine, nitrogen, and
carbon?
• (A) They are gaseous elements at room
temperature.
(B) They have oxides that are acid anhydrides.
(C) They have perceptible color at room
temperature.
(D) They form ionic oxides.
(E) They react readily with hydrogen at room
temperature.
MC #3
Use these answers for questions 11-13
(A) Pb
(B) Ca
(C) Zn
(D) As
(E) Na
11. Utilized as a coating to protect Fe from
corrosion
12. Is added to silicon to enhance its properties
as a semiconductor
13. Utilized as a shield from sources of radiation
MC #4
Which of the following is a correct interpretation
of the results of Rutherford's experiments in
which gold atoms were bombarded with alpha
particles?
(A) Atoms have equal numbers of positive and
negative charges.
(B) Electrons in atoms are arranged in shells.
(C) Neutrons are at the center of an atom.
(D) Neutrons and protons in atoms have nearly
equal mass.
(E) The positive charge of an atom is
concentrated in a small region.
FRQ #1
The postulates of the Bohr model of the hydrogen atom can be
stated as follows:
(I) The electron can exist only in discrete states each with a
definite energy.
(II) The electron can exist only in certain circular orbits.
(III) The angular momentum of the electron is nh/2 where n is any
positive integer.
(IV) Radiation is emitted by the atom only when an electron makes
a transition from a state of higher energy to one of lower energy.
(a) State whether each of these postulates is currently considered to be
correct, according to the wave mechanical description of the
hydrogen atom.
(b) Give the wave mechanical description that has replaced one of the
postulates now considered to be incorrect.
Sources
• Graphics and tables courtesy of:
(Silberberg, Martin S.. Chemistry: The
Molecular Nature of Matter and Change,
5th Edition. McGraw-Hill, 012009. 2.6.3).