Download Atomic Structure -

S.MORRIS 2006
Important Rule To Remember
• There are 2 types of charges: positive
and negative (think about a magnet.)
• - Like charges (positive-positive or
negative-negative) repel;
• - Unlike charges (positive-negative)
attract.
What is an Atom?
An atom is the smallest particle that has
mass and makes up matter.(They are
too small to be seen by human eyes.)
Every type of matter is made up of only
one kind of atom. Example: every gold
atom in gold looks exactly the same.
Parts of the Atom
• The Nucleus
– The center area of an atom, it is where
the most mass is found. It is considered to
be positively charged, because of the
protons (+) that are there (and stay there.)
– There are also neutrons (neutrally charged)
particles that add mass to the nucleus.
PROTONS
• Protons are small, positively-charged (+)
particles inside the nucleus. Because they
are the only charged particles in the
nucleus, the nucleus has a positive
charge. Because the protons remain in
the nucleus, they make up the atomic
number of the element.
Electrons
- Are tiny negatively charged particles (little
mass) outside of the nucleus
- They circle the nucleus because they are
attracted to the positively charged
nucleus.
- Electrons are scattered (they can’ t get
near each other)
Electrons
Because electrons are outside the nucleus,
they can travel. If electrons are attracted
to another nucleus, they will join with
another atom and cause chemical
bonding.
They can’t get near each other, but they are
all attracted to the nucleus, so they circle
the nucleus in pathways or shells.
Electron Cloud
• The area where electrons are located is
called the electron cloud. This area is a
negative energy field.
Electron Shells
Because electrons repel each other, you can
only have so many per shell (path) before
they get into each other’s negative fields.
ATOMIC STRUCTURE
ctrons are arranged in Energy Levels or
ells around the nucleus of an atom. The
tire negative area is called the electron cloud.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
•fourth shell
a maximum of 18 electrons
a maximum of 32 electrons
Valence Electrons
Because valence electrons are on the last
shell, they are the ones that are furthest from
the positive field of the protons. Valance
electrons are the electrons that determine if
an atom can bond with another atom.
This means that the valence electrons could be
attracted to the nucleus of more positive atoms.
If the electrons join the valence electrons of
other atoms, you have chemical bonding.
How Many Valance Electrons?
• Because hydrogen and helium only have 1
shell, they can only have 2 valance
electrons. However, the atoms of all
other elements can have up to 8
valance electrons in their outer shell.
Law of Conservation of Matter
• Matter cannot be created or
destroyed. It can only change
form..
The History of the Discovery of the
Atom
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to smaller
and smaller particles which he called
ATOMA
(greek for indivisible)
HISTORY OF THE ATOM
1808
John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce around
with perfect elasticity and called them
ATOMS
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
PLUM PUDDING
MODEL
HISTORY OF THE ATOM
1910
Ernest Rutherford
oversaw Geiger and Marsden carrying out his
famous experiment.
He fired Helium nuclei at a piece of gold foil
which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit
HISTORY OF THE ATOM
helium nuclei
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to their
surprise, some helium nuclei bounced straight back.
HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a more
detailed model with a central nucleus.
He suggested that the positive charge was all in a central
nucleus, and electrons were attached by attraction.
However, this was not the end of the story.
HISTORY OF THE ATOM
1913
Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by adding
that the electrons were in orbits. Rather
like planets orbiting the sun. With each
orbit only able to contain a set number
of electrons.
Bohr’s Atom
electrons in orbits
The Electron Cloud Model
Section 2: Elements and the
Periodic Table
• An element is matter that is made up of
only one kind of atom.
• There are 117 known elements.
• 90 of them are naturally occurring in
the Earth, while others are synthetic
(man-made).
The Periodic Table
• For many years scientists knew that there
had to be a pattern among the atoms of
elements, but no one could figure out a
system that worked.
• In 1869 there were 56 known elements.
Dmitri Mendeleev, Russian scientist,
arranged the atoms by their size
(atomic weight.)
The Periodic Table
• Mendeleev realized that, when atoms
are arranged by their weight, then their
electron shell configurations were
similar. Similar sized atoms had similar
characteristics.
• Mendeleev also realized that, by
determining the sizes of the atoms, he
could see that some elements had not
yet been discovered.
Column 1: Alkali Metals
What Did Mendeleev Discover?
Mendeleev discovered that:
- The rows of the Periodic Table went from left
to right, increasing the atomic number
(protons.) This means the atoms became
larger as you move across.
- He also found that each column had
elements that had similar physical and
chemical characteristics (many had same
valance electron numbers.)
Column 18: Noble Gases
How Elements Appear on the
Periodic Table
The most important number for each
element is the atomic number, which is
the number of protons that can be
found in every nucleus for every atom
of that element.
The mass number is the number of
protons plus neutrons in the nucleus.
Chemical Symbols
On the Periodic Table, elements are
represented by a CAPITAL letter, or a
capital letter with lower cap letters.
The symbols represent the element’s name
in Latin, so that is why some of the
symbols don’t “match” the English term!
(i.e., potassium = K)
Reading the Periodic Table
The columns (groups or families) show
the electron configuration is similar, so
they have similar physical and
chemical characteristics.
The rows, or periods, are divided into 3
main areas: the metals (the largest),
metalloids, and non-metals. Atomic #
increases
Isotopes
An isotope is when the nucleus of the
atom has a different number of
neutrons than protons. This is very
common for most elements.
Neutrons don’t affect the charge of the
nucleus; they only affect how “large”
(how much mass) the atom has.
Isotopes
Carbon 14
• A carbon 14 atom still has 6 protons, but it
has 14 neutrons.
• Because it is so large, it takes a long time
to decay.
• Carbon 14 decays at a steady rate (halflife), so it is easy to figure out when
something died.
Decay of Carbon 14
Atomic Mass Unit
• If you were to calculate the actual mass of
an element, you have to account for all the
isotopes.
• On the periodic table, all the protons
and neutrons of the element are added
up (including isotopes) and the average
is found.
• This number is rarely a whole number,
due to averaging in isotopes. The
exception are the synthetic elements.
Atomic Mass Unit (AMU)
The Noble Gases
• The elements in the last family (column
18) are unique in that they already have 8
valance electrons.
• This means these gases are found by
themselves, as they cannot bond with
other elements.
• Because of this, we call them the Noble
Gases.
Electron Shells
The N Level
represents the
last, or valance
electrons. The
magic number
(the most this
shell can hold)
is 8.
ATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1.
2.
Electronic Configuration
Dot & Cross Diagrams
ELECTRONIC CONFIGURATION
With electronic configuration elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen
2 in 1st shell
5 in
2nd
shell
configuration = 2 , 5
2
+
5 = 7
N
7
14
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
a)
Ca
20
b)
Na
40
2,8,8,2
d)
Cl
17
35
2,8,7
11
23
c)
2,8,1
e)
Si
14
28
2,8,4
O
8
16
2,6
f)
B
5
11
2,3
DOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and compounds
are represented by Dots or Crosses to show electrons,
and circles to show the shells. For example;
X
Nitrogen
X X
N
XX
X X
N
7
14
What Charge on the Periodic
Table
• We consider the atoms of elements on the
Periodic table to be neutral, so they have
the same number of protons (+) and
electrons (-).
Ions
• Remember, atoms are considered
“neutral” (same number of protons and
electrons) when represented on the
Periodic Table.
• In reality, atoms often lose or gain
electrons. This means the atom becomes
either positively or negatively charged.
Any charged atom (positive or
negative) is an ion.
Ions
If an atom loses an electron, then it will have more
protons than electrons. The atom will be
positively charged when it has more protons.
If an atom gains an electron, then it will have more
electrons than protons. The atom will be
negatively charged when it has more
electrons.
How Sodium (Na) + Chlorine
(Cl) becomes Table Salt
The Periodic Table Song
• http://www.youtube.com/watch?v=GFIvXV
MbII0&safety_mode=true&persist_safety_
mode=1&safe=active