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Atomic Structure
Noadswood Science, 2012
Wednesday, May 24, 2017
Atomic Structure
 To know the structure of an atom
Electrons
Nucleus
containing
protons and
neutrons
Periodic Table
 What is the periodic table and what does it show?
 There are over 100 different elements, arranged in a chart
called the periodic table – the elements are arranged in a
special way…
Chemical Symbols
 Every element has its own chemical symbol – it is usually one
or two letters long (but can sometimes be three)
 Every symbol begins with a capital
 The second and third letters are lower case
Examples
Mg
Mg
MG
mG
O
o
OO
oo
na
NA
nA
Na
AG
Ag
ag
aG
Chemical Symbols
 Sometimes the symbols are really obvious: O = oxygen; Li =
lithium; Mg = magnesium
 However sometimes it is not easy to tell what the symbol
stands for (because the symbol come from a name that is not
an English word)
 E.g. W stands for tungsten (from the word wolfram); Na for
sodium (from natrium)
 The chemical symbols are used all over the world, not matter
what language people speak
Periodic Table Arrangement
 The vertical columns in the periodic table are called groups –
each group contains elements that have similar properties
 The periodic table has eight main groups, e.g. group 1
contains very reactive metals such as sodium (Na) and
potassium (K) whilst group 7 contains very reactive nonmetals such as chlorine (Cl) and bromine (Br)
 The horizontal rows are called
periods (each new period
represents another full shell of
electrons)
 The metals are on the left, the
non-metals on the right
Atoms – Early Ideas
 The word atom comes from atomos, an ancient Greek word
meaning indivisible: the Greek philosopher Demokritos (460370 BCE) maintained that all matter could be divided and
sub-divided into smaller and smaller units, and eventually
there would be a tiny particle that could not be divided any
further - an atom
 Understanding of atoms didn’t progress
much beyond Demokritos’ theory until the
English chemist John Dalton (1766 - 1844)
started to look at it in the 1800s…
Atoms – Early Ideas
 Dalton came to the following conclusions:  All matter is made of atoms, and atoms are indestructible and
cannot be broken down into pieces
 All the atoms of a particular element are identical to each
other and different from the atoms of other elements
 Atoms are rearranged in a chemical reaction
 Compounds are formed when two or more different kinds of
atoms join together
Atoms
 How can we represent an atom?
 What does an atom contain?
 Atoms have a small central nucleus (containing protons and
neutrons) which is orbited by electrons
 All substances are made from atoms, and any
given element is made of atoms of just one
particular sort – represented by a specific
chemical symbol
Atom Structure
 The nucleus: 
In the middle of the atom

Contains protons and neutrons

Has a positive (+ve) charge (due to the
presence of the protons)

Almost the whole mass of the atom is
concentrated within the nucleus

Size is tiny compared to the atom as a
whole!
Electrons
Nucleus
containing
protons and
neutrons
 The electrons: -
Particle
Mass
Charge
Proton
1
+1
Neutron
1
0
Electron
1/2000
-1

Orbit the nucleus

Negatively charged (-ve)

Tiny, but cover a lot of space

The volume of their orbits determines how
big the atom is

Virtually no mass

They occupy shells around the nucleus
Protons & Electrons
 Neutral atoms have no overall charge – the size of the charge
of the electrons is the same as that of the protons, just
opposite (electrons are –ve and protons are +ve)
 This means in an atom the number of protons equals the
number of electrons
 *Electrons can be added / removed – if this is done the
charged atom is known as an ion (watch the sweet demo)!
Atomic Number & Atomic Mass
 Periodic table shows one final important piece of information
- an element’s atomic number and it’s atomic mass…
 The mass number (top number) shows the number of protons
+ neutrons
 The atomic number (bottom number) shows the number of
protons (and therefore, the number of electrons)
Mass number
Atomic number
16
O O
8
Atomic Number & Atomic Mass
 Using the periodic table work out how many neutrons,
protons and electrons and found in the following atoms:  Hydrogen
 Helium
 Lithium
 Carbon
 Oxygen
Protons +
neutrons
Protons
(therefore electrons)
O
Mass number
Atoms
Atomic number
 Remember:  The mass number (top number) shows the number of
protons + neutrons
 The atomic number (bottom number) shows the number of
protons (and therefore, the number of electrons)
 Hydrogen:  Mass number 1 (1 proton and 0 neutrons)
 Atomic number 1 (1 proton & 1 electron)
 Helium:  Mass number 4 (2 protons and 2 neutrons)
 Atomic number 2 (2 protons & 2 electrons)
O
Mass number
Atoms
 Lithium:  Mass number 7 (3 protons and 4 neutrons)
 Atomic number 3 (3 protons & 3 electrons)
 Carbon:  Mass number 12 (6 protons and 6 neutrons)
 Atomic number 6 (6 protons and 6 electrons)
 Oxygen:  Mass number 16 (8 protons and 8 neutrons)
 Atomic number 8 (8 protons and 8 electrons)
Atomic number
O
Bingo
 Take a mini periodic table
 If an element is said, you have to find its symbol using the big
periodic table (on the board) – if you have that symbol on
your mini periodic table you can colour in the square
 The winner is the person who gets all their elements coloured
in first…
 E.g. If I said oxygen, you would look it up, discovering its
symbol is O
 If you have the O symbol on your mini periodic table then
colour it in!
Periodic Table