Download CHEMISTRY – Chapter 2

CHEMISTRY of LIFE
Ch 2.1
Composition of Matter

Matter - Everything in
universe is composed of
matter
 Matter is anything
that occupies space or
has mass
 Mass – quantity of
matter an object has
 Weight – pull of
gravity on an object
Questions
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Is weight and mass the same thing?
Would I weigh more on the moon or
on Earth?
Is my mass the same on the moon
and on Earth?
Elements

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Pure substances that cannot be
broken down chemically into simpler
kinds of matter
More than 100 elements (92
naturally occurring)

Each element
unique chemical
symbol
 Consists of
1-2 letters
 First letter
is always
capitalized

90% of the mass of
an organism is
composed of just 4
elements
 oxygen
 carbon
 hydrogen
 nitrogen
Atoms

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An Atom is the
simplest particle of an
element that retains
all the properties of
that element
Properties of atoms
determine the
structure and
properties of the
matter they compose
Do you know?

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All matter is made up of atoms
Atoms are the smallest part of a
substance that is still that
substance
Atoms are very, very small
The Nucleus

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Central core of the
atom
Consists of positive
charged protons and
neutral neutrons
Positively charged
Contains most of
the mass of the
atom
The Protons

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All atoms of a given element have the
same number of protons
Number of protons called the atomic
number
Protons and electrons are equal to
create a neutral element
Practice
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Periodic table on back cover
or page 1086
Atomic number of oxygen (O)
 8
Atomic number of zinc (Zn)
 30
# protons in bromine (Br)
 35
protons in gold (Au)
 79
Element with 44 protons
 Ruthenium (RU)
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The Neutrons

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The number varies slightly among atoms
of the same element
Different number of neutrons produces
isotopes of the same element
Isotopes

Isotopes of the same element have the
same chemical properties

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Because they have the same number of
electrons!
Some isotopes are radioactive
 Unstable and break down at a
constant rate
 Used to treat cancer, determine the
ages of rocks and fossils, kill
bacteria, as molecular labels
Atomic Mass

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Protons & neutrons are found in the
nucleus of an atom
Protons and neutrons each have a
mass of 1 amu (atomic mass unit)
The atomic mass of an atom is found
by adding the number of protons &
neutrons in an atom
The Electrons

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Negatively charged high energy
particles with little or no mass
Travel at very high speeds at various
distances (energy levels) from the
nucleus
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Electrons in the same energy level
are approximately the same
distance from the nucleus
Outer energy levels have more
energy than inner levels
Each level holds only a certain
number of electrons
Energy Levels

Octet Rule – except for the first
shell which is full with two electrons,
atoms interact in a manner to have
eight electrons in their valence
(outermost) shell
Chemically Inert Elements

Inert elements have their outermost
energy level fully occupied by electrons
Figure 2.4a
Chemically Reactive Elements

Reactive
elements do
not have
their
outermost
energy level
fully occupied
by electrons
Figure 2.4b
Periodic Table

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Elements are arranged by their atomic
number on the Periodic Table
The horizontal rows are called Periods
& tell the number of energy levels
Vertical groups are called Families &
tell the outermost number of
electrons
Compounds

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Most elements
do not exist
by themselves
Readily
combine with
other elements

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A compound is a pure
substance made up of
atoms of two or more
elements in a fixed
proportion
Chemical formula shows
the kind and proportion
of atoms of each
element that occurs in a
particular compound
H2O
Chemical Formulas

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Subscript after a symbol tell the
number of atoms of each element
H20 has 2 atoms of hydrogen & 1
atom of oxygen
Coefficients before a formula tell
the number of molecules
3O2 represents 3 molecules of oxygen
or (3x2) or 6 atoms of oxygen

The physical and
chemical
properties of a
compound differ
from the
physical and
chemical
properties of
the individual
elements that
compose it
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Sodium (Na) is a silver colored metal
soft enough to cut with a knife. It
reacts explosively with water
Chlorine is a poisonous, greenish gas
that was used to kill many soldiers in
WWI
Sodium and chlorine combine to form
the compound sodium chloride that is
safe for us to eat – Table Salt
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The tendency of
elements to combine
and form compounds
depends on the
number and
arrangement of
electrons in their
outermost energy
level
Atoms are most
stable when their
outer most energy
level is filled
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Most atoms are not
stable in their natural
state
Tend to react with
other atoms in order to
become more stable
In chemical reactions
bonds are broken; atoms
rearranged and new
chemical bonds are
formed
Covalent Bonds

Formed when two atoms share one
or more pairs of electrons
Compounds
formed by
covalent bonds
are called
MOLECULAR
COMPOUNDS or
MOLECULES
Polar Molecules
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Unequal sharing of
electrons
Have a slight electrical
charge on either side of
the molecule 105O
 H2O
Polar molecules dissolve in
water
 Hydrogen bonding
From: http://ghs.gresham.k12.or.us/science
/ps/sci/ibbio/chem/notes/chpt2/water.htm

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(–)
O
H
H
(+)
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Nonpolar molecules
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No unequal sharing
Do not dissolve in water
Oils and fats
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Ionic Bonds
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Some atoms become stable by
losing or gaining electrons
Atoms that lose electrons are
called positive ions or Cations
Compounds that
from ionic bonds
are called IONIC
COMPOUNDS

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Atoms that gain electrons are called
negative ions or Anions
Because positive and negative
electrical charges attract each other
ionic bonds form
What word means:
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To clarify
with
examples
Illustrate

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To draw a
conclusion by
reasoning; to
speculate
Infer
What word means:

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Discuss good
and bad
points,
strenths, &
weaknesses,
judge worth
or quality
Evaluate

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To give facts
that make
clear, to
make known
in detail
Explain
Quiz!
protons Neutrons
carbon
oxygen
Atomic Mass
Elecnumber number trons