Download Dalton`s Atomic Theory

Physical Science
Ch 4 Atoms
(including some PC info)
Dalton’s Atomic Theory
Dalton developed a theory to explain why the
elements in a compound always join in the
same way.
Dalton proposed the theory that all
matter is made up of individual
particles called atoms, which can
not be divided.
Dalton’s Atomic Theory
• All elements are composed of atoms.
• All atoms of the same element have the
same mass, and atoms of different
elements have different masses.
• Compounds contain atoms of more than
one element.
• In a particular compound, atoms of
different elements always combine in the
same way.
Thomson’s Model of the Atom
• He used an cathode rays to learn that
negatively charged particles came from
atoms.
• Thomson’s experiments provided the first
evidence that atoms are made of even
smaller particles.
• Thomson’s “plum pudding” model
suggested that the negative charges in an
atom were evenly scattered throughout an
atom filled with a positively charged mass
of matter.
Rutherford’s Atomic Theory
• Rutherford’s model concluded that all of
an atom’s positive charge is concentrated
in its nucleus.
• He used the gold foil experiment to
determine the behavior of the alpha
particles when they struck different
locations in the gold foil. He originally
thought that the path of the alpha particles
would only be slightly bent. He was
wrong. Some of the particles bounced
straight back.
Subatomic Particles
• Protons are positively charged subatomic
particle that are found in the nucleus.
• Electrons are negatively charged subatomic
particles that are found in the space outside the
nucleus.
• Neutrons are neutral subatomic particles that
are found in the nucleus.
• Protons, electrons, and neutrons can be
distinguished by mass, charge, and location in
an atom.
Atomic Number and Mass Number
• The atomic number of an element is the same as the
number of protons in an atom of that element.
Atoms of different elements have different numbers of
protons.
• The mass number of an atom is the sum of the
protons and neutrons in the nucleus of that atom.
To find number of neutrons:
Mass of neutrons = Mass number – Atomic number
Isotopes
Isotopes are atoms of the
same element that have
different numbers of
neutrons and different mass
numbers.
H-1
H-2
H-3
0n
1n
2n
Same atomic #, however = 1.
Bohr’s Model of the Atom
• Bohr’s model focused on the electrons in an
atom.
• Bohr’s model stated that electrons move with
constant speed in fixed orbits around the
nucleus, like planets around a sun.
• When an atom gains or loses energy, the
energy of an electron can change.
• Possible energies that electrons in an atom
have are called energy levels.
• An electron in an atom can move from one
energy level to another when the atom gains
or loses energy.
Electron Cloud Model
An electron cloud is a visual model
of the most likely locations for
electrons in an atom.
Energy Level
# of orbitals
Max # of e’s
1
1 (En. Lev.
Squared)
2 (2 x # of
2
4
8
3
9
18
4
16
32
orbitals)
Electron Configuration
• An electron configuration is the
arrangement of electrons in the
orbitals of an atom.
• The most stable electron
configuration is the one in which
the electrons are in orbitals with
the lowest possible energies.
The Periodic Table of
Elements and Atom Types
I. Organization of the Periodic Table
A. periodic law – properties of elements
tend to change in a regular pattern
when elements are arranged in
order of increasing atomic number.
B. Elements are arranged in periods and
groups
1. period – a horizontal row of the
elements in the periodic table
a. another name for periods are valences
2. Every atom has valence electrons
a. Electrons are arranged in energy levels.
i. Each energy level can hold only a specific
number of electrons
ii. Electrons start at the energy level closest to
the nucleus and fill up one energy level
after another.
b. valence electron – an electron
in the outermost energy
level of an atom
B. Elements are arranged in periods and
groups
1. period – a horizontal row of the
elements in the periodic table
a. Another name for periods are valences
b. Each period has a number, which refers
to how many energy levels are in that
element.
2. group (family) – a vertical column of the
elements in the periodic table
a. Groups of elements in the periodic
table, have similar properties
b. Valence electrons largely effect
chemical and physical properties.
c. Elements in the same
group have the
same number of
valence electrons.
II. Ions!!!
A. Ion – an atom that has lost or gained one
or more electrons and therefore has a net
electric charge.
E. Atoms have no overall charge
1. An un-reacted, elemental atom has the
same number of protons as electrons
2. Each proton has 1 positive charge and
each electron has 1 negative charge.
3. Positive charges and negative charges
cancel each other out.
2 protons =
7
2 neutrons =
7
+ 2
7 electrons =
2 charges
+7
0 charge
-2
7 charges
0 charge
II. Ions!!!
A. Ion – an atom that has lost or gained one
or more electrons and therefore has a net
electric charge.
B. Ionization – the
process of adding or
losing one or more
electrons from an
atom
C. Atoms want all of their energy levels to be
full.
Adding or losing electrons helps
this to happen.
C. Ions have charge!
1. cation – an ion that
has given
up
or
17 protons
=
+ 17one
charges
more electrons 18 neutrons =
0 charge
18 electrons
= than
- 18 charges
a. Cations have+ more
protons
-1
charge
electrons.
b. Cations have an overall positive charge.
2. anion – an ion that has gained one or
more electrons
11 protons
= than
+ 11 charges
a. Anions have fewer
protons
12 neutrons =
0 charge
electrons.
10 overall
electronsnegative
=
- 10 charge.
charges
b. Anions have+an
+1
charge
III. Differences in atomic structure
A. Atomic number
1. atomic number – the number of protons
in an atom
2. Each element has its own atomic
number.
B. Atomic mass or weight
1. atomic mass – the mass of an atom of
a given element
2. The average atomic mass is never a
whole number.
C. Isotopes!!
1. isotopes – any atoms
having the same number
of protons but different
numbers of neutrons
13
12
C
2. average atomic mass – the mass of the
average atom of a given element
a. Atomic mass unit (amu) – a unit
equivalent to 1/12 the mass of a carbon12 atom (~1 proton or neutron)
b. It reflects number of protons and
neutrons in naturally occurring elements.
12 protons
12 protons 12 protons
+12 neutrons +13 neutrons +14 neutrons
24 amu
25 amu
26 amu
78.65% x 24 amu
10.14% x 25 amu
+ 11.13% x 26 amu
24.305 amu
26
Mg
25
Mg
24
Mg
Mole – amount of a substance
• A mole of atoms contains Avogadro’s
number of atoms: 6.02 x 1023 atoms
• Used to convert mass <-> moles <->
number of atoms or particles.
• From the periodic chart, the atomic mass
tells the number of grams in a mole of an
element.
• For O, 15.999 g/mol
• For P, 30.974 g/mol
Problem:
• Find the mass of oxygen in 2.7 mol.
2.7 mol 15.999g
mol
2.7 x 15.999 =
4.3197 =
4.3 g O
(2 sig figs because of 2.7)
Another problem.
• Find the number of moles in 230.0 g of O.
230.0g
mol
15.999g
230.0 =
15.999
1.4376 =
1.438 mol O
(4 sig figs because of 230.0)