Chapter 2 Problems

1
Chapter 2 Problems

• 22, 32, 46, 50, 56, 60, 72, 86, 90, 103

2
What Is Everything Made Of?

• An atom is the smallest particle of matter that
  has the same properties as the larger sample.

3
Important Laws

• Dalton realized that compounds always contain
  atoms that are in small, whole-number ratios
  (never a fraction!).

This is called the Law of Multiple Proportions.
4
Important Laws

• A few years earlier, Louis Proust had realized
  that molecules of a given substance always
  contain the same atoms in the same ratio.

For example, water always contains two hydrogens
and one oxygen.
You can change this ratio. For example, you can
have two hydrogens and two oxygens but then
its not water anymore!
This is called the Law of Definite Proportions.
5
Atoms Contain Electrons

• In 1897, J.J. Thomson discovered atoms contain
  electrons, particles that have a negative charge.

This was called the plum pudding model.
6
The Rutherford Experiment

• In 1910, Ernest Rutherford tried to find out how
  thick this positively-charged blob is by
  shooting a-particles at it.

Since a-particles have a positive charge, he
guessed theyd slow down as they went through the
atom, and he would measure their speed.
BUT...
7
Rutherfords Experiment
8
Atoms Contain A Nucleus

• Rutherfords experiment showed that an atom is
  mostly empty space. The positive charge isnt
  spread out its all in a tiny nucleus at the
  center of the atom.

9
The Bohr Model

• In 1913, Niels Bohr proposed that electrons
  circle the nucleus in orbits, like planets around
  the sun.

10
The Periodic Table

• The Atomic Number (Z) tells you how many
  protons an atom has.

11
Isotopes

• In addition to protons, a nucleus also contains
  neutral particles called neutrons. An atom can
  have different numbers of neutrons.

Because they have different numbers of neutrons,
they are different isotopes.
However, all three are the same element. Why?
12
Isotope Symbols
1
2
3
H
H
H
1
1
1
1 proton
1 proton
1 proton
1 electron
1 electron
1 electron
0 neutrons
1 neutron
2 neutrons

• To write the symbol of an isotope, first write
  the elements symbol

On the lower left, write the atomic number.
On the upper left, write the mass number (the sum
of the number of protons plus neutrons).
13
The Mass Number

• Protons and neutrons have almost the same mass.
  Electrons weigh much less.

This means the mass of the atom is the mass of
the protons neutrons...
...the mass number!
39 amu
14
The Periodic Table

• The Atomic Mass tells you the average mass of an
  element (in amu).

15
The Periodic Table

• Metalloids

16
Elements Necessary For Life
17
Molecules

• A molecule is the smallest possible particle of a
  compound. Its made up of atoms bonded together.

However, when theyre in a compound, atoms
usually do have a charge!
18
Ions

• If you add or remove an electron from an atom,
  the atom gets a charge. The charged particle is
  called an ion.

-
Cl

Na
19
Ion Charges
1
2
-2
-1
3
20
Molecules

• When atoms combine to form a molecule, the
  charges on the atoms must always cancel out,
  because molecules are always neutral.

2-
Li
O

-
3
2-
Notice the cation is usually written first.
21
Polyatomic Ions

• Lots of ions have more than one atom (unlike Na
  or Cl-). They are called polyatomic ions.

22
Polyatomic Ions
There are lots of polyatomic anions
You want to learn these formulas and charges soon!
23
Naming Molecules

• How do we figure out the name of a compound from
  the formula?

NaCl
sodium chloride
Basically, we write the name of the cation, then
the name of the anion. If its a monatomic
(one-atom) anion, change the end of the atoms
name to ide.
Ag2S
ammonium chromate
24
Naming Molecules

• Transition metals can have more than one possible
  charge. This can cause a difficulty when naming
  compounds.

CoF2 CoF3
According to our rules so far, these two
compounds would both be called cobalt fluoride.
To avoid confusion, we usually write the charge
on the transition metal as a Roman numeral in the
molecules name.
25
Naming Molecules

• Lets sum up the rules we know so far.

• Cation
• Has the same name as the element (with the
  exception of ammonium).

• Write the charge as a Roman numeral for most
  transition metals (plus Sn and Pb).

• Anion
• Change the ending to -ide if monatomic.

• Polyatomic anions have special names.

26
Naming Molecules
Cr(OH)3
chromium (III) hydroxide
Mg3(PO4)2
magnesium phosphate
potassium permanganate
KMnO4
iron (II) bromide
FeBr2
27
Types of Molecules

• So far, weve only looked at compounds made up of
  a metal (the cation) and a non-metal (the anion).
  These were ionic compounds.

28
Molecular Compounds
Molecular compounds are named almost the same way
as ionic ones. Write the name of the atom
further to the left on the periodic table first,
then the other atom, with the ending changed to
-ide.
Each atom also gets a prefix telling how many of
them there are.
29
Molecular Compounds
P2O5
diphosphorus pentoxide
N4S4
tetranitrogen tetrasulfide
carbon monoxide
dinitrogen monoxide
nitrogen dioxide
nitrogen monoxide
30
Ionic Compounds
A few important ionic compounds can have water
molecules chemically bonded to them
CuSO4
These compounds are called hydrates, and they
will have an extra word in their names to tell
you how many waters they have.
CuSO4
copper (II) sulfate
CuSO45H2O
copper (II) sulfate pentahydrate
31
Important Acids
Finally, please learn the names and formulas of
these important acids (well use them in lab
soon)
HCl hydrochloric acid HNO3 nitric
acid H2SO4 sulfuric acid H3PO4 phosphoric acid
32
Formulas
Consider these molecules
CH2O formaldehyde C2H4O2 acetic
acid C3H6O3 lactic acid C5H10O5 ribose C6H12O6 glu
cose
These all have different molecular formulas.
However, they all have the same empirical formula
(the smallest whole-number ratio of the different
elements)
CH2O