1. Atoms, elements and the Periodic
Table.
Print pages 9-13 2 page handouts

2. What is an Atom.
• Atoms are the basic building blocks of ordinary matter. Atoms can join
together to form molecules, which form most of the objects around
you.
• Atoms are composed of particles called protons, electrons and
neutrons. Protons carry a positive electrical charge, electrons carry a
negative electrical charge and neutrons carry no electrical charge at
all. The protons and neutrons cluster together in the central part of
the atom, called the nucleus, and the electrons orbit the nucleus. A
particular atom will have the same number of protons and electrons
and most atoms have at least as many neutrons as protons.

3. proton
Neutron
Electron
A proton is a part of an atom. The other parts of an atom are the neutron, and electrons.
It's an electrically charged particle. It is positive. It is located within the nucleus of the
atom, which is about one ten thousandth of the diameter of the atom itself but contains
virtually all of the atom's mass. The number of protons in the nucleus determine the
element.
A neutron is a subatomic particle; it is one of the building blocks of the atom. As such, it is
found in the nucleus of an atom. It has no electric charge. It has a half ;life of 886 seconds.
An electron is a subatomic particle that has a negative charge. An electron has like a weird orbit
around the proton/neutron but doesn`t fully orbit them it pops up here and there.

4. Atoms and Elements.
The word ATOM was first used in the fifth century BC by a Greek thinker called Leucippus. He
Thought everything was made of tiny particles that could not be divided. However, nobody
believed him. John Dalton put forward his theory about atomic theory in 1807.
The structure of a helium atom.
Each element has its own symbol. This is a shorthand way of writing down the elements, and is
the same whatever language spoken by the scientists. The symbol have one or two letters. For
example Oxygen is O and sodium is Na. The first letter is a capital letter.

5. The
periodic
table

7. Name of element
Symbol for the element
(Atomic mass)Protons and neutrons
added together
(Atomic number)
The number of protons
Must contain 2 electrons
The meaning of the symbols

8. All elements arranged into increasing atomic number.
The vertical columns are called groups. They are called groups because
They are similar to each other. For example group 1 are all very re-active metals
And group 2-3 they contain a lot of metals.

9. Atomic Structure
Atoms are made up of three different kinds of particles called Neutrons, protons and electrons.
The masses of these particles are really tiny. We say protons and neutrons have a mass of 1.
Electrons are smaller they do have a mass but that is so small we can ignore it. We say that
Electrons have a negligible mass. Protons and electrons have electric charges. Protons have (+)
Charge, and electrons have a (-) charge. Atoms always have the same amount of protons and
Electrons so the charges cancel each other out. Atoms have no overall electrical charge. Each
Atom in an element has the same number of protons. A different element will have a different
Number of protons in it`s atom. The number of protons in an atom is called it`s atomic number.
A hydrogen nucleus. Hydrogen atoms
always Have just one proton in The nucleus.
The atomic Number of hydrogen is 1
A carob nucleus. Carbon
Atoms always have six protons.
The atomic number of carbon is 6
An oxygen atom nucleus Oxygen atoms always have Eight
protons. The atomic number Of oxygen is 8
The mass of an atom depends on the number of protons and neutrons. The total number of
Protons and neutrons is an atom is called its mass number. Carbon has six protons and six
Neutrons so it has a mass number of 12. sometimes atoms of an element have different numbers
Of neutrons. Isotopes are atoms of the same element that have different numbers of neutrons.
Most elements have different isotopes.

10. Electronic structure
Some elements are very reactive, and some hardly react at all. Elements behave differently
Because of the way their electrons are arranged. Electrons have a negative charge, and protons
Have a positive charge. An atom normally has the same number of protons and electrons, so it
Has no overall charge.
Hydrogen has just one Proton.
One electron moves around it
Helium has two protons and
Two neutrons in it`s nucleus.
It has two electrons moving
Around the nucleus.
Lithium has three protons and
Three electrons. Two of the
Electrons are close to the nucleus,
And the third one is further away.
These different locations for
Electrons are called energy levels/
Shells. The inner shell can only hold
Two electrons they the outer shells
Hold up to 8

11. The periodic table.
12
MG
2,8,2
ATOMIC NUMBER (NUMBER OF PROTONS)
SYMBOL (MAGNESIUM)
ELECTRONIC STRUCTURE
The elements are arranged in the periodic table in order of the atomic number. The position of
An element in the periodic table can also tell us something about how the element reacts. Only
The electrons in the outer shell of an atom will take part in chemical reaction. They also form
Similar compounds. Some properties change as you go down a group. For instance, elements at
The top of a group may have lower melting and boiling points than ones at the bottom. The
Elements can be split into metals and non-metals.
12
MG
2,8,2
nucleus
This diagram shows the inner shell
Has two electrons in because the first
Number of the electronic structure is 2
Then the second shell has 8 electrons in
Because the second number is 8 and
The third shell has 2 electrons in
Because the last number is two on
The electronic structure.

12. Looking for patterns
One way scientists learn more about the world is to look for patterns, and then try to explain
Why these patterns exist. Johan Döbereiner was one of the first scientists to look for patterns
Of properties in the elements. He noticed that chlorine, bromine and iodine had similar
Properties. In 1864 John Newlands decided to put all the elements in order of masses of atoms.
When he did this he found that the elements could be divided into groups, with every 8th
Element having similar properties. He called this the law of Octaves.
1 H F Cl Co&Ni Br Pd I Pt&Ir
2 Li Na K Cu Rb Ag Cs TI
3 G Mg Ca Zn Sr Bd Ba&V Pb
4 Bo Al Cr Y Ce&La U Ta Th
5 C Si Ti In Zr Sn W Hg
6 N P Mn As Di&Mo Sb Nb Bi
7 O S Fe Se Ro&Ru Te Au Os
Most scientists
ignore Newlands
theory because his
law did not work for
all the elements. A
Russian scientist
Dmitri Mendeleev
arranged elements
like their modern
order. He around them
In order of mass number but he also looked at their properties. If the order of mass numbers
put Elements in the wrong place for their properties, he ignored the masses.

13. Looking for patterns
He also left gaps in the table where there was no elements that fitted the pattern. He predicted
The mass numbers and other properties of these missing elements. In 1874 a French scientist
Called Paul-Emile Lecoq discovered Gallium one of the missing elements and found that it had
Properties very similar to the properties predicted by Mendeleev. It was not until the structure of
The atom was discovered in 1910 that scientists realised that Mendeleev`s order for the elements
Depended on the atomic number (the number of protons in the nucleus) rather than mass
Number.