Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chemistry - Topic 1 - Atomics Structure and the Periodic Table (History…
Chemistry - Topic 1 - Atomics Structure and the Periodic Table
Atoms and Elements
Atoms are particles with a radius of approximately 1nm that make up all other substances.
Each element has its own atom. Different elements are decided by their proton (or atomic) number.
Each atom is made up of subatomic particles:
Neutrons: 0 charge, 1 mass
Electrons: -1 charge, 0 (negligible mass)
Protons: +1 charge, 1 mass
Isotopes:
Every element has several isotopes. These are atoms of the same element, but with different atomic masses due to having a different amount of neutrons.
Some isotopes are unstable, and decay (quickly or slowly) emitting radiation.
Because some elements have several isotopes, the mean atomic mass is calculated. The equation for this is:
Relative atomic mass = (mass1
abundance1 + mass2
abundance2) / (abundance1+abundance2)
History of the atom
J J Thomson
Concluded from his experiments that atoms weren't solid spheres. His measurements of charge and mass showed negatively charged particles. Now that plum pudding model showed the atom as a ball of positive charge with electrons in it.
Rutherford
Alpha particle experiment, nuclear model.
John Dalton
The atomic structure has changed over time - At the start of the 19th century John Dalton described atoms as solid spheres and said that different spheres made up the different elements.
Bohr
That electrons were contained in the shell otherwise it would collapse, electrons orbit the nucleus in fixed shells.
Further experiments
James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons. The discovery of neutrons resulted in a model of the atom of the atom which was pretty close to the modern day accepted version known as the nuclear model.
Rutherford and others showed that the nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus. These particles were named protons.
Periodic table
There are around 100 elements, which all materials are made from.
In the periodic table the elements are laid out in order of increasing atomic number. Arranging the elements like this means there are repeating patterns in the properties of the elements. (The properties are said to appear periodically, hence the name periodic table)
If it wasn't for the periodic table organising everything, you'd have a hard time remembering properties of elements.
It's handy for working out which elements are metals and which are non metals. Metals are found to the left and non metals are to the right.
Elements with similar properties form columns called groups.
The group number tells you how many electrons there are in the outer shell. For example, Group 1 elements all have one electron in their outer shell and Group 7 all have seven electrons in their outer shell. The exception to the rule is Group 0. For example Helium has two electrons in its outer shell. This is useful as the way atoms react depends on the number of electrons in their outer shell. So all elements in the group are likely to react in the same way.
If you know the properties of one element, you can predict properties of other elements in its group. In the exam, you may be asked to do this.
Isotopes
A very popular example of a pair of isotopes are
carbon-12
and
carbon-13
.
Because many
elements
can exist as a number of different isotopes,
relative atomic mass
(
A
,) is used instead of mass number when referring to the element as a whole. This is an
average
mass taking into account the
different masses
and
abundances
of all the isotopes that make up the element.
So Isotopes have the
same atomic numbe
r but
different mass numbers
.
You can use this formula to work out the relative atomic mass of an element.
Relative atomic mass (
A,
) = sum of (isotppe abundance x isotope mass number) / sum of abundances of all the isotopes.
Isotopes
are different forms of the same element, which have the
same number
of protons
but a
different number of neutrons.
Compounds and Ions
Atoms of different elements can join together into compounds. When these atoms are bonded together, they are called a molecule.
Atoms can bond into molecules in two ways: Ionic bonding and covalent bonding. What type of bonding is used depends on where the elements are in the periodic table.
Covalent bonding occurs between non-metals. They share electrons to fill their outer shells. This can be displayed in a dot and cross diagram.
Ionic bonding occurs between metals and non-metals. Some electrons are transferred from the metal to the non-metal. The metal becomes a positive ion and the non-metal becomes a negative ion.
An ion is an atom with a charge. This is because it has a different number of electrons to protons.
Arrangement in periodic table
Prot
o
n (atomic) number increase gradually from left to right across a period (row)
Elements in the same group (column) have the same number in the outer shell electrons and therefore have similar properties and reactions.
GROUP 1 (ALKALINE METALS)
Lithium Sodium Potassium
All have 1 electron on the outer shell
Very reactive as they only need to lose 1 electron for a full outer shell
In water
float and fizz on surface of the water, forming an alkaline solution and hydrogen gas (squeaky pop test)
Metal + water ----> metal hydroxide + hydrogen
2Na +2H2O -----> 2NaOH + H2
In oxygen
Metal + oxygen ---> metal oxide
4 Na + O2 ------> 2 Na2O
With Halogens
Metal + halogen ---> metal halide
2 Na + Cl2 -----> 2NaCl
Form positive ions (1+) when they react
GROUP 0 (NOBEL GASES)
E.g helium, neon, argon
Nonreactive gases. Do not want to gain, lose or share electrons as their outer shell is full.
Often used in packaging, and light bulbs because of their unreactivity
Transition metals
e.g copper, iron, zinc
Compared to group 1 they are:
harder and stronger
Higher melting point
Higher density
Far less reactive
This makes the better construction material
They also have
coloured compounds
, often make good
catalysts
and can have
ions with variable charge
, eg. Fe2+ and Fe3+
Group 1 compounds are typically white and have metal ions that always have a 1+ charge
Make sure you can
Describe how the modern peridoic table is arranged in the same group and similar properties.
Describe the typical properties of group 1,7 and 0
For separate science
Describe the typical properties of transition metals and compare them to group one metals
Group 7 (Halogens)
e.g fluorine, chlorine, bromine, iodine
All have 7 on the outer shell
Very reactive as they only have to gain one electron for a full outer shell.
They
form negative ions when they react with other metals
.
Form covalent molecules when they react with non-metals and share electrons.
Can
form diatomic molecules with themselves
as it gives them a full outer shell.
They have a generally low melting/boiling point, however this increases as you go down the group as the forces between the molecules become stronger.
Halogens also undergo
displacement
reactions
Reactivity
Determined generally by the number of electrons on the outer shell and by the size of the atom
Number of electrons on the outer shell
Group 1 reactivity trend (alkali metals)
All have one on the outer shell, therefore they want to
lose one
in order to have a full one.
As you move down group 1:
Atoms get bigger
Outer electrons further from the positive nucleus
Less attraction between nucleus and outer electrons
Outer electron is lost more easily
Atoms get more reactive
How to demonstrate the trend
React the metals wiht water. All will float and move on the surface of the water, this will make an alkaline soloution (metal hydroxide) and hydrogen (fizzing)_
Lithium will fizz gently, moving on the surface of the water
Sodium will fizz more vigourously and move faster
Potassium will move even faster again, and set on fire
GROUP 7 REACTIVITY TREND (Halogens)
All have seven outer shell electron, so want to
gain one
electron for a full outer shell
As you move down group 7
Atoms get bigger
Outer electron further from positive nucleus
Less attraction between nucleus and outer electron
Outer electron gained more easily
Atoms get less reactive
How to demonstrate the trend
More reactive halogens displace less reactive ones in displacement reactions. Chlorine will displace the less reactive bromine and a colour change would be seen.
chlorine + sodium bromine ---> Sodium chloride + bromine
Bromine would be formed as an orange solution
Chlorine + sodium iodine ----> iodine + sodium chloride
Here you would see iodine as a brown solution
