Transcript Atoms and Elements - Oakland Community College

FSN 1500 Week 3
Atoms, Elements and Chemical
Bonding: An Introduction to
Chemistry
Introduction
 Why is chemistry often called the “central
science”?
 An understanding of chemistry enables us
to better understand ourselves and the
surrounding universe
 The chemistry you’ll review today will be a
component of multiple other topics we
discuss this semester
Atoms and Elements
 Atom - smallest particle of matter that
retains all the properties of a particular
chemical element
 Element - basic chemical building block of
matter; can’t be altered into other
substances by chemical or ordinary physical
means
 Presently 118 chemical elements identified
(114 formally named); typically 92
elements are identified as naturally
occurring
Partial Periodic Table of Elements
Under what extraordinary physical circumstances can atoms be altered
(even split apart)?
Atoms and Elements
 The most powerful
electronic microscopes
(Scanning Tunneling
Microscope) can “see” the
external surfaces of some
atoms
 Atoms can be thought of as
spherical bodies having
approximate diameters of
one ten-billionth of a meter
37 Xenon atoms arranged into the IBM logo
Subatomic Particles and Atom
Structure
 All atoms consist of smaller particles of
matter called subatomic particles;
subatomic particles bear none of the
characteristic properties of any chemical
element
 Perhaps as many as 300 different subatomic
particles; conceptually much chemistry can
be explained by knowledge of three
subatomic particle types
Subatomic Particles and Atom
Structure
 How do we deduce the
atom’s structure, and the
existence of subatomic
particles and their
properties since we can’t
see them?
 Ingenious experimentation
provides the answers!
(e.g., closed can analogy,
and the 1909 Rutherford
Gold Foil Experiment)
The Rutherford Gold Foil Experiment
deduced the existence of the atomic
nucleus and its extraordinary density
Subatomic Particles
 The masses and electrical charges of
subatomic particles are conventional
expressions of very small actual values
 The atomic mass unit (amu) is the
conventional expression of the approximate
mass of one proton
 The three subatomic particles we must
understand: protons, neutrons and electrons
Subatomic Particles
 Proton - positive electrical charge (1) and
mass of 1 amu
 Neutron - no electrical charge and mass of 1
amu
 Electron - negative electrical charge (-1)
and negligible mass
Atomic Structure
 Atoms of all elements have the same basic
structure; atoms of different elements have
different numbers of protons, neutrons and
electrons
 The protons and neutrons cluster together in a
dense, central core area called the nucleus
 The protons and neutrons constitute nearly all the
atom’s mass
 The electrons move continuously and rapidly
around the nucleus
Crude Atom Model
Atomic Structure (Refined)
 The electrons move continuously through
differently shaped clouds of space (electron
energy levels) that lie at specific distances
from the nucleus (see figures)
Atomic Structure
 The specific levels
outside the nucleus
that host the electrons
are often referred to
as “energy” levels
(see figure)
Carbon Atom Example
Why aren’t all the atom’s electrons
found at one distance from the nucleus?
Figure 3.5A
Atomic Structure
 The comparable sizes of the nucleus and the
entire atom can be considered by thinking
of a dime (nucleus) placed in the center of a
major-league baseball park (the circular
confines of the stadium are equivalent to the
entire atom’s boundaries)
Ongoing Atomic Structure Research
 During spring 2010, the
Large Hadron Collider in
Europe, the most powerful
atomic accelerator in the
world, began colliding
ions or subatomic particles
(protons) together at
nearly the speed of light to
further investigate the
nature of the atom and
matter – hoping to detect
the Higgs boson particle.
Ongoing Atomic Research
• In July, 2012 the Large
Hadron Collider scientists
announced they were
highly confident their
experiments had detected
the Higgs boson and
validated existence of the
“Higgs field”
• The way particles interact
with the Higgs field
determines their mass
according to the Standard
Model of particle physics
Ongoing Atomic Research
 Pay attention to the
lay press for more
updates on the
nature of the atom!
Element Symbols
 All chemical
elements can be
represented by one,
two, or three letter
symbols (e.g., C =
Carbon)
Element Symbols and Atomic
Structure
 In text form, a superscript to the left of the
symbol and a subscript to the left of the
symbol allow us to mentally reconstruct the
atomic structure
 Example: 23892U
Element Symbols and Atomic
Structure
 The subscript number is called the atomic
number and represents the number of
protons in the atom’s nucleus
 The superscript number is called the atomic
mass and represents the sum of the neutrons
and the protons in the nucleus
 E.G., 23892U
Element Symbols and Atomic
Structure
 Electrically neutral atoms contain the same
number of protons and electrons
 Example: What is the name of the element
and the number of protons, neutrons and
electrons represented by the symbol
16 O?
8
Chemical Compounds
 Compound - a substance composed of two
or more atoms chemically combined in
definite proportions (e.g., water - H2O)
 Why do H and O (or any other elements)
combine to form water? The answer lies
within the atom structure
 There is a maximum number of electrons
that can occupy each energy level
Chemical Compounds
 The maximum number of electrons that can
occupy an energy level is calculated from
the formula 2n2 , where n equals the energy
level; the energy levels are numbered
consecutively outward from the nucleus
beginning with the number 1 (see figures)
 The energy levels are defined by the presence of
electrons; no electrons, no energy level
What is the maximum
number of ewhich can
reside in
each energy
level?
Chemical Compounds
 Atoms that contain the maximum number of
electrons in their energy levels, or eight
electrons in their outermost energy level,
are considered energetically stable
 Energetically stable elements have no
tendency to chemically react; energetically
unstable elements will react to become
stable (see board examples)
Chemical Bonding Background
 Is carbon a
chemically
reactive or
unreactive
element?
Chemical Compounds
 The mechanisms by which energetically
unstable elements combine to achieve
energetic stability is called chemical
bonding; chemical bonding is necessary to
form a chemical compound
 In nature, four primary bonding
mechanisms operate: ionic, covalent,
metallic and Van der Waals bonding
Chemical Bonding Types
 Ionic - involves ions; an ion is an atom or
group of atoms that carries an electrical
charge
 Two Ion types: cation (+ charge); # of
protons > # electrons ; anion (- charge); # of
electrons > # protons
Chemical Bonding Types
 Ions form when an atom structure loses or
gains electrons; cations are represented with
a + sign used as a superscript to the right of
the chemical symbol, this is usually
preceded by a numeral indicating the
magnitude of the charge (e.g., Na 1+ )
Chemical Bonding Types
 Anions are represented by a - sign used as a
superscript to the right of the chemical
symbol, this is usually preceded by a
numeral indicating the magnitude of the
charge (e.g., Cl1- )
 Ionic bonding involves the complete
transfer of one or more electrons from one
atom structure to another
Chemical Bonding Types
 The atom structure that loses electron(s)
becomes a cation, the atom structure that
gains electron(s) becomes an anion
 The oppositely charged ions are attracted to
each other (by electrical forces) in the
proportions needed to produce an
electrically neutral combination (see figure)
Sodium
Chlorine
Sodium Chloride
18 e-
11 e-
17 e-
10 e-
Ionic Bonding Example
Ionic Bonding Example
Chemical Bonding Types
 Review Na + Cl = NaCl example
 Important points: all ionic chemical
compounds are electrically neutral, even
though their constituents are electrically
charged; the properties of compounds are
substantially different than the properties of
the compound’s constituent elements alone
Chemical Bonding Types
 Covalent bonding - bonding mechanism
involving a sharing of electrons between
adjacent atom structures; the sharing is
accomplished by the overlap of energy
levels between the atom structures
 Review water example (see figure)
Covalent Bonding Model
Chemical Bonding Types
 Metallic bonding - variation of the covalent
bond; more electrons present than needed to
meet the energy level requirements; the
“extra” electrons are free to migrate across
the bonded atom structures
 The mobility of electrons conveys many of
the characteristic properties of metals (e.g.,
good conductors of electricity and heat)
Metallic Bond Model
N
Cu
atoms
e-
e-
N
N
eN= nucleus
N
mobile
electron
Chemical Bonding Types
 Van der Waals - very
weak electrical
attraction between the
electrons of one atom
structure and the
protons of another
atom structure’s
nucleus due to
distorted energy levels
and sublevels (see
figure)
Van der Waals Bond Model
Van der Waals bonds never exist exclusively in a chemical
compound - one or more other bond types is always present
Relative Bond Strengths
 On average the strength of chemical bonds is
(strongest to weakest): covalent, ionic, metallic,
Van der Waals
 Relevance? Since energy is required to break
bonds, how strongly a compound’s constituents
are bonded will partially determine the stability
(i.e., reactivity) of that compound
 Example: what really happens when salt (NaCl) is
placed into water?
Important Considerations
 The chemical and physical properties of
compounds are determined by their chemical
composition, types of bonding and orientation of
the bonding
 Review graphite and diamond example (see
figures)
Additional Terminology
 molecule - smallest
electrically uncharged
unit of matter that
retains all the
properties of a
chemical compound
 A molecule has the
same relationship to a
compound that an
atom has to what?
Chemical Elements
Composed of atoms
Smallest particle of matter
that retains parent element’s properties
Can’t be altered by chemical
or ordinary physical means
Atoms or ions can bond
to form compounds
Compounds consist of two or more atoms/ions
chemically combined
The compound’s type of bonding,
bond orientation and composition
control its properties