Download Periodic Table and Atomic Structure Summary

John Ogilvie High School
National 5
The Periodic Table was devised by the Russian chemist Dmitri Mendeleev in 1869. It lists all the
known elements. As of 2013, there are 118 known elements.
The Periodic Table lists these elements in order of increasing atomic number.
The Periodic Table is arranged into vertical columns called groups and horizontal rows called
periods.
Elements can be classified in different ways:
Classification Type
Examples
naturally occurring/made by scientists
solid/liquid/gas
metal/non-metal
All elements with atomic number above 92 are made by scientists
and are not found naturally on Earth.
The majority of elements are solid. There are 11 gases (mainly
found on the right of the Periodic Table). Two elements exist as
liquids, they are bromine and mercury.
Metals are found on the left of the zig-zig line.
Non-metals are found on the right of the zig-zag line.
Some groups have specific names:
Group
Name
1
2
Between 2 and 3
7
0 or 8
Alkali Metals
Alkaline Earth Metals
Transition Metals
Halogens
Noble or Monatomic Gases
Examples
lithium
calcium
gold
fluorine
helium
sodium
magnesium
iron
chlorine
neon
potassium
strontium
copper
bromine
argon
Elements in the same group in the Periodic Table have similar chemical properties.
Group 1 – The Alkali Metals
The alkali metals are soft metals which are shiny when freshly cut but lose their shininess when
exposed to air as a layer of metal oxide forms.
metal + oxygen  metal oxide
For this reason alkali metals are stored under oil to prevent contact with the air or water.
Alkali metals react violently with water. When they react with water they form alkaline
solutions, this is why they are called the Alkali Metals.
e.g. sodium + water  sodium hydroxide + hydrogen
(an alkali)
Group 7 – The Halogens
The halogens and their compounds have many uses. Fluorine compounds are used in toothpaste
to help avoid tooth decay. Chlorine is used in drinking water and swimming pools as it can kill
harmful bacteria. Bromine is used in dyes and medicines. Iodine can be used as an antiseptic.
Astatine is a radioactive element that does not occur naturally on Earth.
Like hydrogen, nitrogen and oxygen, the halogens are diatomic molecules. This means they exist
in a molecule of two atoms. This means that we can write a chemical formula for them: F2, Cl2,
Br2, I2, At2.
Green
Red
Learning Statement
Amber
Unit 1: Section B – The Periodic Table & Atomic Structure
Group 0 (or 8) – The Noble (or Monatomic) Gases
The gases in this group are all colourless. They are unreactive and form almost no known
chemical compounds. These gases can be used in lasers and lighting.
Every element is made up of small particles called atoms.
Each element contains one type of atom only, e.g. sulfur contains only sulfur atoms and copper
contains only copper atoms.
Atoms have the following structure:
Atoms are made up of 3 different particles.
Particle
proton
neutron
electron
Location
nucleus
nucleus
outside nucleus
Charge
+1
0
-1
Mass
1 amu
1 amu
approximately zero
Atoms are neutral because they have the same number of protons and electrons. The
positive charge of the nucleus is equal to the sum of the negative charges of the electrons.
Electrons are held in electron shells which are sometimes called energy levels.
1st energy level holds
2 electrons
2nd energy level holds
8 electrons
3rd energy level holds
8 electrons
4th energy level holds
8 electrons
** Electron arrangements for the first 20 elements can be found on page 6 of the data booklet**
Elements in the same group have the same number of outer electrons e.g. Group 1 – The Alkali
Metals.
Lithium
2,1
Sodium
2,8,1
Potassium
2,8,8,1
Elements with the same number of electrons in their outer shell have similar chemical properties.
Each element in the Periodic Table has its own atomic number.
atomic number = number of protons
The mass of atom is due to the particles found in the nucleus, the protons and the neutrons.
mass number = no. of protons + no. of neutrons
The symbol of an element can be written showing the mass number and atomic number. This is
called nuclide notation.
The number of protons, neutrons and electrons in neutral atoms can be calculated by doing the
following:
An ion is a charged particle. For example, Ca2+, Cl-, Na+ or O2-.
An ion is formed when a neutral atom loses or gains electrons.
o Metals always lose electrons to form positive ions e.g. Na+, Mg2+
o Non-metals gain electrons to form negative ions e.g. F-, O2Nuclide notation can also be drawn for ions. The charge is written at the top right of the
symbol.
The number of protons, neutrons and electrons in charged ions can be calculated by doing the
following:
Isotopes are atoms of the same element which have:
o the same atomic number but a different mass number
o the same number of protons but a different number of neutrons.
e.g.
The relative atomic mass (RAM) is the average mass of all the isotopes of an elements
o RAM is rarely a whole number because it is an average.
e.g. The RAM of chlorine is 35.5
o The two isotopes of chlorine are 35Cl and 37Cl
o As the RAM is closer to 35 than 37, there must be more
37
Cl.
35
Cl atoms in the sample than