GCSE CHEMISTRY TOPIC ONE: ATOMIC STRUCTURE AND THE PERIODIC TABLE

C1- ATOMIC STRUCTURE AND THE PERIODIC TABLE


Atoms:

The Nucleus The Shells
1. In the centre of the atom 1. Contain electrons
2. Contains the protons and neutron 2. Electrons move around the nucleus on the
3. Radium is around 1 x 10^-14 m shells
4. Positive charge due to the protons 3. Electrons are negatively charged and are tiny,
5. Almost the whole mass of the atom is but cover a lot of space
concentrated in the nucleus 4. The volume of the electrons orbit depends on
the size of the atom
Atoms have radius of around 5. The electrons have almost no mass
0.1 nm (1 x 10^-10 m). One
nanometre is 1 x 10^-9 m


PARTICLE RELATIVE MASS RELATIVE CHAARGE
Proton 1 +1
Neutron 1 0 (No charge)
Electron Very small (almost no mass) -1


Finding the P, N and E: An ion is an atom or group of
12 Protons = 12 Neutron = 12 Electron = 12 atoms that has lost or gained
E.g. Mg 24
electrons, giving it a charge.
(In this case: 12 = P and E and 24 -12 = N)

1. Atoms are neutral- have no overall charge (unlike ions)
2. This is because they have the same number of protons and electrons
3. The charge on the electrons is the same size as the charge on the proton, but
opposite- so they cancel out
4. In an ion, the number of protons doesn’t equal the number of electrons. This means
it has an overall charge. For example an ion with a 2- charge, has two more
electrons than protons ( as electrons have a negative charge)
Atomic and mass number:
Elements: Mass number Alloy = Mixture of two or more
23
Example- Na elements where at lest one is a metal
11 Atomic number

Element = A substance made up of atoms that all have the same number of protons in their
nucleus.
Atomic number is protons, and electrons are equal to the number of protons in order to
cancel out their charges and make the atom neutral.
The mass number minus the atomic number gives us the neutrons.

Na: P= 11 E=11 N=12

,  Atoms can have different numbers of protons, neutrons and electrons. It’s the
number of protons in the nucleus that decides what type of atom it is
 For example- An atom with one proton in its nucleus is hydrogen and an atom with
two protons is helium.
 If a substance only contains atoms with the same number of protons it’s called an
element
 So all the atoms of a particular element (e.g. nitrogen) have the same number of
protons and different element have atoms with different number of protons
 Each element consists of only one type of atom.


Isotopes:
Isotopes = Different forms of the same element, which have the same number of protons,
but a different number of neutrons
Meaning isotopes have the same atomic number but different mass numbers
Example- A common example of a pair of isotopes are carbon- 12 and carbon- 13.

Normal atom: Isotope:
12 13
C P=6 E=6 N=6 C P=6 E=6 N=7
6 6

Using isotopes to calculate the relative atomic mass (Ar or RAM):
Relative atomic mass is an average mass taking into account the different masses and
abundances (amount/volume) of all then isotopes that make up the element.
Formula: RAM = (% of Isotope 1 x mass of Isotope 1) + (% i 2 x mass of i 2 )
100




Compounds:
Compound = A compound is a substance formed when two or more elements are chemically
bonded together
 When elements react atom combine with other atoms to from compounds
 Making bonds involves giving away, taking or sharing electrons. Only the electrons
are involved- the nuclei of the atoms aren’t affected at all when a bond is made
 It is difficult usually to separate the original elements out of a compound again so a
chemical reaction is needed to do this
 During a chemical reaction at least one new substance is made. You can usually
measure change in energy, such as a temperature charge, as well