Download Atoms, Molecules and Ions

Atoms and Elements
CHM 109
SUROVIEC
SPRING 2014
I. Atoms and Atomic Theory
2
 An element is composed of tiny particles called
atoms

All atoms of the same element have the same chemical
properties
 Compounds are formed when two or more atoms of
different element combine
 Chemical reactions involve only separation,
combination or rearrangement or atoms
A. Fundamental Laws of Matter
3
 There are three fundamental laws of matter
 Law of conservation of mass

Law of constant composition

Law of multiple proportions
A. Law of conservation of mass
4
 In a chemical reaction matter is neither created or
destroyed
B. Law of Definite Proportions
5
 In 1797 Joseph Proust noticed that elements of a
given compound always combined in definite
proportions in all samples of a compound.
C. Law of Multiple Proportions
6
 This law asserts that when 2 elements (A&B) form
two different compounds, the masses of element B
that combine with 1 gram of element A can be
expressed as a ratio of small whole numbers.
D. Atomic Theory
7
 John Dalton explained the 3 previous laws along
with his Atomic Theory which states:
II. Structure of an atom
8
 Atom: basic unit of an element that can enter into
chemical combination
 Atom possesses structure:



Electron
Proton
Neutron
A. Electrons
9
 First evidence for subatomic particles came from the
study of the conduction of electricity by gases at low
pressures




J.J. Thomson, 1897
Rays emitted were called cathode rays
Rays are composed of negatively charged particles called
electrons
Electrons carry unit negative charge (-1) and have a very small
mass (1/2000 the lightest atomic mass)
Cathode Ray Apparatus
10
02_05.JPG
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III. Structure of the Atom
12
 Since the overall atom is neutral, and we know that
they contain electrons they must have a positive
particle to balance the atom out.
II. Structure of the Atoms
13
A. Protons and Neutrons – The Nucleus
14
 Ernest Rutherford, 1911
 Bombardment of gold foil with α particles

Expected to see the particles pass through the foil
Rutherford Backscattering
15
Found that some of the alpha particles were deflected by the foil
B. Current Atomic Model
16
Most of the atom’s mass and all of its positive
charge are contained in a small cone called the
nucleus
2. Most of the volume of atoms is empty space which
is where the electrons are
3. There are as many electrons as protons
1.
Rutherford’s Model of
the Atom
17
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
If the atom is a football stadium, then the nucleus is a
marble on the 50-yard line.
VI. Proton, Neutron and Electron
18
 Amu = 1/12 the mass of a carbon atom containing 6
protons and 6 neutrons. This makes the proton
~1amu.
 The proton and electron have electrical charge
A. Elements
19
 What makes elements unique is the number of
protons, neutrons and electrons in an atom of the
element.
B. Isotopes
20
 All atoms of a given element have same number of
protons, but the number of neutrons can change
 This means that one element can have different
masses.
B. Isotopes
21
 Atomic number (Z) = number of protons in the
nucleus
 Mass number (A) = number of protons and neutrons
in the nucleus
 Isotope = atoms of the same element (X) with different
numbers of neutrons in their nuclei
Mass Number
Atomic Number
A
ZX
Element Symbol
Do You Understand Isotopes?
How many protons, neutrons, and electrons are
14
in 6 C ?
How many protons, neutrons, and electrons are
11
in 6 C ?
22
C. Molecules and Ions
23
 Molecules: aggregate of two or more atoms in a
definite arrangement held together by chemical
forces
H2
H2O
NH3
CH4
 Ion: atom or group of atoms with a net charge due to
the loss or gain of electrons.
C. Molecules and Ions
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 Cation: ion with a
 Anion: ion with a
positive charge
negative charge
Do You Understand Ions?
How many protons and electrons are in
27 3+
13 Al ?
How many protons and electrons are in
78
2Se
?
34
25
Polyatomic ions
26
V. Periodic Law and Table
27
 Mendeleev constructed a periodic table based on the
elements known at the time.
 He noticed that certain groups of elements had
similar properties
A. Ions and Periodic Table
28
 Metals tend to lose electrons
 Nonmetals tend to gain electrons
VI. Atomic Mass
29
 Since isotopes have different masses for the same
element an atomic mass is a weighted average of the
isotopes
VII. Molar Mass
30
 We would like to know
A. The Mole.
the number of atoms in a
given mass of atoms.
 Since atoms are so small
we count them by weight.
We use a mole to count the
amount of material
containing 6.022 x 1023
B. Mole conversion
31
 Using conversion factors
we can convert between
moles and atoms.
C. Moles and Mass
32
 The next question is what is the mass of that many
atoms.
 It has been determined that the mass of 1 mole of
atoms is equal to its atomic mass in amu