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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 STRUCTUREATOMIC STRUCTURE
Electrons are arranged in Energy Levels
or Shells around the nucleus of an atom.
The entire negative area is called the
electron cloud.• first shell a maximum of 2 electrons
• second shell a maximum of 8
electrons
• third shell a maximum of 18 electrons
•fourth shell 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..
HISTORY OF THE ATOMHISTORY 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
ATOMAATOMA
(greek for indivisible)
HISTORY OF THE ATOMHISTORY 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
ATOMSATOMS
HISTORY OF THE ATOMHISTORY OF THE ATOM
1898 Joseph John Thompson
found that atoms could sometimes eject a
far smaller negative particle which he
called an
ELECTRONELECTRON
HISTORY OF THE ATOMHISTORY OF THE ATOM
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
1904
like plums surrounded by pudding.
PLUM PUDDING
MODEL
HISTORY OF THE ATOMHISTORY 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 ATOMHISTORY OF THE ATOM
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.
helium nuclei
HISTORY OF THE ATOMHISTORY 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 ATOMHISTORY 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.
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 (half-life), 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 STRUCTUREATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells. For
example;
N
Nitrogen
7
14
2 in 1st shell
5 in 2nd shell
configuration = 2 , 5
2 + 5 = 7
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements;
Ca O
Cl Si
Na20
40
11
23
8
17
16
35
14
28B
11
5
a) b) c)
d) e) f)
2,8,8,2 2,8,1
2,8,7 2,8,4 2,3
2,6
DOT & CROSS DIAGRAMSDOT & 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;
Nitrogen N XX X
X
XX
X
N7
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=GFIvXVMbII0&safety_mode=true&persist_safety_mode=1&safe=active
