GCSE Chemistry Paper 2 Edexcel Notes.
Key Concepts:
1.1 Describe how the Dalton model of an atom has changed over time because of the
discovery of subatomic particles
Dalton believed all atoms of an element are identical, different elements have different atoms.
Thomson Plum pudding model- big sphere of sponge, with loads of fruit. The sponge was made
of positive charges with embedded negative charges (electrons).
Rutherford gold foil experiment- Fired alpha particles (positive helium nuclei) at gold foil, most
of them passed straight through. If it was like the plum pudding model it should not have
passed through, leading to the understanding of the atom being very largely spaced.
Some alpha particles were deflected. This means the alpha particles must have hit something
else positive to be deflected. 2 same charged particles deflect/repel, 2 different, attract. Very
few particles were deflected, this tells us the nucleus is small.
1.2 Describe the structure of an atom as a nucleus containing protons and neutrons,
surrounded by electrons in shells
1.3 Recall the relative charge and relative mass of:
a a proton
b a neutron
c an electron
, Atoms have equal numbers of protons and electrons. They have equal numbers of positive and
negative charges to have an overall neutral charge.
1.5 Describe the nucleus of an atom as small compared to the overall size of the atom
The nucleus relative to the atom is:
1/60600.
The nucleus is so small it can be compared to a pea in the middle of a stadium. The pea
represents the nucleus and the stadium represents the atom, showing how small the nucleus is
compared to the overall size of the atom.
1.6 Recall that most of the mass of an atom is concentrated in the nucleus
Electrons have little mass compared to protons and neutrons. Most of the mass of an atom is
concentrated in its nucleus.
1.7 Recall the meaning of the term mass number of an atom
Mass number: The total number of protons and neutrons in the nucleus.
1.8 Describe atoms of a given element as having the same number of protons in the nucleus
and that this number is unique to that element
Atoms of a given element have the same number of protons in the nucleus, as they have the
same atomic number. The number of protons in each element is unique to its element.
1.9 Describe isotopes as different atoms of the same element containing the same number of
protons but different numbers of neutrons in their nuclei
Isotopes are atoms of an element with the same number of protons but different numbers of
neutrons. They will have the same atomic number but different mass numbers.
1.10 Calculate the numbers of protons, neutrons and electrons in atoms given the atomic
number and mass number
Number of protons = Atomic Number
Number of electrons= Atomic Number - (because the number of electrons = number of
protons)
The number of neutrons = Mass number- the atomic number.
1.11 Explain how the existence of isotopes results in relative atomic masses of some elements
not being whole numbers
Relative atomic mass, Ar, values consider the relative abundance or percentage of each isotope
in a sample of an element. The existence of isotopes means that the relative atomic mass
values of elements may not be whole numbers.
1.12 Calculate the relative atomic mass of an element from the relative masses and
abundances of its isotopes
The relative atomic mass of an element can be calculated using this formula:
(Isotope Mass X Percentage) + (Isotope Mass X Percentage)
100
Even if you have more than 2 isotopes, you must put it over 100.
TOPIC 6
6.1 Explain why some elements can be classified as alkali metals (group 1), halogens (group 7)
or noble gases (group 0), based on their position in the periodic table
Group one elements have 1 electron in their outer shell, they lose 1 electron to become
neutral.
Key Concepts:
1.1 Describe how the Dalton model of an atom has changed over time because of the
discovery of subatomic particles
Dalton believed all atoms of an element are identical, different elements have different atoms.
Thomson Plum pudding model- big sphere of sponge, with loads of fruit. The sponge was made
of positive charges with embedded negative charges (electrons).
Rutherford gold foil experiment- Fired alpha particles (positive helium nuclei) at gold foil, most
of them passed straight through. If it was like the plum pudding model it should not have
passed through, leading to the understanding of the atom being very largely spaced.
Some alpha particles were deflected. This means the alpha particles must have hit something
else positive to be deflected. 2 same charged particles deflect/repel, 2 different, attract. Very
few particles were deflected, this tells us the nucleus is small.
1.2 Describe the structure of an atom as a nucleus containing protons and neutrons,
surrounded by electrons in shells
1.3 Recall the relative charge and relative mass of:
a a proton
b a neutron
c an electron
, Atoms have equal numbers of protons and electrons. They have equal numbers of positive and
negative charges to have an overall neutral charge.
1.5 Describe the nucleus of an atom as small compared to the overall size of the atom
The nucleus relative to the atom is:
1/60600.
The nucleus is so small it can be compared to a pea in the middle of a stadium. The pea
represents the nucleus and the stadium represents the atom, showing how small the nucleus is
compared to the overall size of the atom.
1.6 Recall that most of the mass of an atom is concentrated in the nucleus
Electrons have little mass compared to protons and neutrons. Most of the mass of an atom is
concentrated in its nucleus.
1.7 Recall the meaning of the term mass number of an atom
Mass number: The total number of protons and neutrons in the nucleus.
1.8 Describe atoms of a given element as having the same number of protons in the nucleus
and that this number is unique to that element
Atoms of a given element have the same number of protons in the nucleus, as they have the
same atomic number. The number of protons in each element is unique to its element.
1.9 Describe isotopes as different atoms of the same element containing the same number of
protons but different numbers of neutrons in their nuclei
Isotopes are atoms of an element with the same number of protons but different numbers of
neutrons. They will have the same atomic number but different mass numbers.
1.10 Calculate the numbers of protons, neutrons and electrons in atoms given the atomic
number and mass number
Number of protons = Atomic Number
Number of electrons= Atomic Number - (because the number of electrons = number of
protons)
The number of neutrons = Mass number- the atomic number.
1.11 Explain how the existence of isotopes results in relative atomic masses of some elements
not being whole numbers
Relative atomic mass, Ar, values consider the relative abundance or percentage of each isotope
in a sample of an element. The existence of isotopes means that the relative atomic mass
values of elements may not be whole numbers.
1.12 Calculate the relative atomic mass of an element from the relative masses and
abundances of its isotopes
The relative atomic mass of an element can be calculated using this formula:
(Isotope Mass X Percentage) + (Isotope Mass X Percentage)
100
Even if you have more than 2 isotopes, you must put it over 100.
TOPIC 6
6.1 Explain why some elements can be classified as alkali metals (group 1), halogens (group 7)
or noble gases (group 0), based on their position in the periodic table
Group one elements have 1 electron in their outer shell, they lose 1 electron to become
neutral.
