Transcript Unit 3 - Section 5.1 Introduction to Chemistry

Introduction to Some Chemistry Ideas
Understanding chemistry…
Would you ban the following compound – Dihydrogen monoxoide (also called hydric acid)?
• It is a colourless, odourless chemical compound
• It is a highly reactive radical
• is a key ingredient in most pesticides
• It can mutate DNA, denature proteins, disrupt cell membranes and chemically alter critical
neurotransmitters
• It contributes significantly to many environmental problems such as acid rain and soil erosion,
and it contributes to the Earth’s Greenhouse Effect
• It is used in vast quantities by every industry on Earth
• It is partially responsible for the spread of pollutants present in contaminated rivers, lakes and
oceans
• In its gas state, it can produce painful burns to exposed skin
• Its atomic components are found in many caustic explosives and poisonous compounds such
as sulfuric acid, nitroglycerine and ethyl alcohol
• It can cause severe illness or death in either very low or very high concentrations
• It is legally discarded as waste be individuals, businesses and industries
• It can cause death if inhaled (…even in very small quantities)
• If there is prolonged exposure to its solid state, it can cause severe tissue damage
• It decreases the effectiveness of automobile brakes
• It contributes to corrosion and oxidation of many metals
Introduction to Some Chemistry Ideas
Chemistry
• The study of matter AND how
it reacts or combines when
different forms and types of
matter come together.
• A physical science that deals
with the composition,
structure and properties of
substances and the reactions
they undergo
Introduction to Some Chemistry Ideas
Matter
Anything that has mass
and volume.
Mass is the amount of
matter a substance
contains. NOTE: Mass
and weight are different.
Weight is due to
gravitational pull
Volume is the amount of
space that an object
takes up
Introduction to Some Chemistry Ideas
Physical Change
• Affects physical appearance of the
substance BUT not the substance’s
composition. That is, the MATTER of
the substance is not altered.
Chemical Change
• Alters the composition of the matter
(e.g., decomposing water using
electrical energy – 2H2O
2H2 + O2
Introduction to Some Chemistry Ideas
Mixture
• Physical combination of two or
more kinds of matter. NOTE: It
is not chemical bonding.
• Two types: Homogeneous and
Heterogeneous. Homo is
Greek for “same” while Hetero
is Greek for “different”
Introduction to Some Chemistry Ideas
Pure Substance
• Delimited composition that is
retained in response to physical
change.
• Two types: Element and Compound.
An element cannot be separated into
a simpler substance. A compound is
two or more elements that combine
CHEMICALLY in a set ratio to form a
different substance AND you are able
to break it down into elements using
chemical processes
Introduction to Some Chemistry Ideas
Atom
• The smallest particle of an element that
retains the identity and properties of the
element.
• Atoms consist of three subatomic
particles: (1) protons, (2) neutrons and
(3) electrons
Introduction to Some Chemistry Ideas
Proton
• Positive charge
• Mass of 1. In grams, proton mass is 1.67 X 10-24g
• Located in nucleus
Neutron
• No charge (neutral)
• Mass of 1. In grams, neutron mass is 1.67 X 10-24g
• Located in nucleus
Electron
• Negative charge
• So small, mass is considered to be 0. In grams, electron mass is 9.02 X 10-28g
• Located in shells or orbits located around the nucleus
• Moving
Introduction to Some Chemistry Ideas
Considering the mass of neutrons and protons (1.67 X 10-24g),
there must be 602,000,000,000,000,000,000,000 neutrons and
protons (…or 6.02 X 1023) in 1g.
In chemistry, this is a VERY IMPORTANT number: 6.02 X 1023 is
Avogadro’s Number (…after the person who measured it). It is the
number of atoms per mole of a given substance. A mole is a unit
of measurement to express amounts (…rather than mass or
volume).
Thinking it through – 1 / 6.02 X 1023 = 1.67 X 10-24 which is called
Atomic Mass Unit (u). 1u = 1.67 X 10-24g
Introduction to Some Chemistry Ideas
This represents the element Helium.
The Atomic Symbol is He
The Atomic Number is 2. That is the
number of protons (…and electrons)
The Atomic Mass is 4. It is the
number of protons + the number of
neutrons. Helium has 2 protons. Thus,
helium has 2 neutrons (4 – 2 = 2)
Introduction to Some Chemistry Ideas
Isotope
Atoms of an element that have the
same number of protons BUT a
different number of neutrons.
The diagram shows three isotopes of
hydrogen: protium (no neutrons),
deuterium (1 neutron) and tritium (2
neutrons).
Since neutrons has no electrical
charge, the chemistry of the element
is not impacted. However, the mass
of the element changes.
Isotopes can be stable or unstable.
Unstable isotopes decay. They are
radioactive. NOTE: All
anthropogenic elements are
radioactive isotopes.
Introduction to Some Chemistry Ideas
Noble Gases
The Noble Gases are elements that
have a stable electron configuration
(i.e., their outer shell of electrons if
full – called a Stable Octet).
Because they are stable, Noble Gases
are non-reactive (i.e., they do not
form compounds naturally).
Noble Gases exist as individual atoms
in nature. Most of the other elements
cannot exist as individuals. Metals
that CAN are gold, silver and
platinum.
Introduction to Some Chemistry Ideas
Trends in the Periodic Table
One trend is Atomic Radius.
As shown, the size of the
atom increases, as expected,
as you move down a column
(called Family or Group).
Unexpectedly, atomic radius
decreases as you move
across a row (called a
Period). Why?
Introduction to Some Chemistry Ideas
Trends in the Periodic Table
Other aspects include
•Ionization Energy – amount of energy
required to remove an electron from a
gaseous atom or ion
•Electron Affinity – measure of the
change in energy that occurs after an
electron is added
•Electronegativity – measure of an
atom’s ability to attract electrons in a
chemical reaction
These three aspects all increase as you
move UP a Family and across left-toright a Period. Why?
Introduction to Some Chemistry Ideas
Elements are neutral. That is, the number
of positively-charged protons is the same
as the number of negatively-charged
electrons (p+ = e-) so the overall charge is
zero.
In an ionic chemical bond, some elements
give or take electrons to become an ION. If
a non-metal adds a negative charge (i.e.,
takes an electron), the ion becomes
negatively-charged. It is called an ANION.
If a metal gives away a negative charge
(i.e., gives an electron), the ion is
positively-charged. It is called an CATION.
Introduction to Some Chemistry Ideas
Chemical Bonds
There are three types of chemical bonds: (1)
ionic, (2) covalent (polar or non-polar) and (3)
metallic.
The difference in electronegativity between
the elements determines the TYPE of chemical
bond that will occur.
– ΔEN between 1.7 and 3.3 forms an ionic
bond
– ΔEN between 0.5 and 1.7 forms a polar
covalent bond
– ΔEN is between 0 and 0.5 forms a nonpolar covalent bond
Introduction to Some Chemistry Ideas
Chemical Bonds
An ionic bond occurs when ions giveand-take electrons.
A covalent bond occurs when electrons
are shared. A non-polar covalent bond
occurs when the electron is shared
equally between; whereas, a polar
covalent bond occurs when the electron
is not shared equally. In a polar
situation, one element has a negative
charge while the other element is
positive