Transcript Chemistry: The Basics

Chemistry
Why do you think we have to
learn about Chemistry in a
Biology class?
A Brief History:
Ahem… Er, Mr.
Democritus, I
don’t believe this
is a laughing
matter.
• Democritus (Fourth Century BC)
– First named the “atom”
you kindly
• From Greek word “atomos” Would
meaning
unable to cut
remove yourself?
• An atom is the basic unit of matter
You’re blocking
– Lacked evidence
my information.
• John Dalton (1766-1844)
– Performed experiments to discover:
• Dalton’s Atomic Theory
Dalton’s
Atomic Theory
Um,
who
I’m Oxygen.
is this?
It
sure
is
1. All
composed of tiny
I amindivisible
different
Heelements
looks
nice
particles
from you, but
pretty called atoms.
hanging
Tell me
I’m sure we
different
out with
about it,
could find
from you
you,
Carbon!
some
way to
and me,
2. Atoms
of
the
same
element
are
identical
Carbon.
bond!
Carbon.
Still more of Dalton’s Atomic
Theory…
3. Atoms of different elements can
physically mix together or can chemically
combine to form compounds.
4. Chemical reactions occur when:
– atoms are separated, joined or rearranged;
– however, they are never changed into atoms
of another element.
Reflecting on Dalton’s Theory
Most of Dalton’s theory is still accepted.
Which part do you think has been
rejected?
The Atom is Divisible!
Return to Theory #1 and cross out the word “indivisible”
The three kinds of subatomic
particles
1. Protons (p+)
– Discovered in 1886, Eugen Goldstein saw
cathode rays traveling against the flow.
– What do you think the proton’s mass is in
relation to the electron? 1,840
________________
times as big
– Actual mass = 1.67 x 10-24 grams
– One unit of positive charge
2. Neutrons (n0)
– Discovered by James Chadwick in 1932.
– Actual mass = 1.67 x 10-24 grams
– No charge
The three kinds of subatomic
particles
3. Electrons (e-)
– Discovered by J.J. Thomson in 1897.
– He used a cathode ray tube
– In 1916, Robert Millikan discovered the
mass was 1/1840 H, and the charge was
one unit of negative charge.
– Actual mass: 9.11 x 10-28 __________
grams
So how are all these parts put
together?
In 1911, Rutherford performed an
experiment:
What did this
prove?
Source of
alpha
particles
Thin sheet of gold foil
Atoms are mostly empty space
• Rutherford proposed that the atomic
structure was like “planets around the sun”
– This did not account for very specific traits
that atoms possessed.
Atomic Structure
Protons and Neutrons make up the nucleus
Electrons spin around in orbitals surrounding
the nucleus
The Bohr Model
• In 1915, Neils Bohr modified Rutherford’s
“planetary” model of the atom
• He added the new discovery of orbitals
Outer orbitals =
Max out at 8
Innermost Orbital =
Maxes out at 2
What makes atoms different from
each other, if they have the same
basic parts?
The Atomic Number
Definition: The number of
protons in the nucleus of
an atom of that element.
Why protons?
Why not neutrons?
Or electrons?
• Oxygen’s Atomic Number is 8.
– How many protons does it have? _______
8
8
– How many neutrons does it have? ________
8
– How many electrons does it have? ________
• Wait a minute, how do we know we have
that many of each atomic component?
Atomic Mass (AMU)
• The total number of protons and
neutrons is called the atomic
mass.
Based on this nucleus, what
is the atomic mass? 4
+ +
What element is it? Helium
What about those special cases?
• Sometimes there are more or less
neutrons in a nucleus, these are called
isotopes.
The Atomic
Number
Element’s
Name
Atomic Mass
5
5
P = _____
B
6
N = _____
Boron
10.81
5
E = _____
Bohr Diagram
Lewis
Structure
B
Welcome!
• Please pick up your folder and go to your
Science group!
• Clean out your folder, leaving only your
“Periodic Table Basics” worksheet in there.
were
HiYou
there!
Greetings, Nitrogen.
Bonding
and Chemical
right!
I am
We
are Hydrogen
I’mReactions
now
Ammonia!
atoms. Perhaps we
Nitrogen.
But, am I an
•willChemical
Bonding:
change the
way
Am
I
an
atom or a
you
think
about
Combining Atoms of Elements
to
form
atom
or
a
compound
yourself.
Chemical Compoundscompound?
now?
Oh, you can’t be
serious!
Bonding
To achieve stability, an atom will
either gain, lose or share electrons.
Ionic Bonds:
A bond that involves a transfer of electrons
Ionic Bonds
Sodium Chloride = Salt!Chloride
Chlorine
Ion (+1)
Ion (-1)
Can you guess which
Covalent Bonds
element I am?
What
will
complete
my
• A covalent bond is a chemical bond
valence shell?
formed by sharing electrons.
Different types of Covalent Bonds
Single Bond: One pair of shared electrons
Double Bond: Two pairs
= of
H shared
– H electrons
Triple Bond: Three pairs of shared electrons
O=C=O
C
Lone
pairs: Cyanide
Electron (HCN)
pairs not
shared
Hydrogen
can
form this.
between
Can
you? atoms
H
N
H
H
Bonding Basics Practice
1-
Ionic Bonds
1. Mg + Br
2+
Br
2. Pb + S
1-
Mg
2-
4+
S
Pb
Br
MgBr2
2-
S
PbS2
1-
Cl
3. Al + Cl
Cl
Al
Cl
1-
3+
1-
AlCl3
Bonding Basics Practice
Covalent Bonds
1. H + Cl
Cl H – Cl
H
Cl
2. C + Cl
Cl
C
Cl
Cl
O
Si
Cl
C
Cl CCl4
Cl
Cl
3. Si + O
HCl
O
O = Si = O
SiO2
Bond with your classmate!
• Each of you will have an element.
• The charge – or oxidation number – is on
the element.
• Your goal is to bond with as many of your
classmates as possible.
• Balance your equations!
– i.e., Magnesium (Mg) and Bromine (Br) must
make… MgBr2
Bond!